Book - Handbook of Pathological Anatomy 2.15
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Meckel JF. Handbook of Pathological Anatomy (Handbuch der pathologischen Anatomie) Vol. 2. (1812) Leipzig.
- Ligaments: I. Trunk | II. Head | III. Extremities Muscles: I. Trunk | II. Head | III. Extremities Angiology: I. Heart | II. Body or Aorta Arteries | III. Body Veins| IV. Pulmonary Artery | V. Pulmonary Veins | VI. Lymphatic System | VII. A Comparison of Vascular System Nervous System: I. Central Nervous System
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Section I. Central Part of the Nervous System
§ 1711. The central part of the nervous system is composed of the 3pinal marrow contained in the spinal canal, and of the encephalon contained in the skull. Bartels has proposed to designate it by the
(1) Besides tbe writers mentioned in the first volume who, in their general remarks on the nervous system, have given a complete description of the central part of this system, and who have even described in part its periphery, as Willis and Vieussens, we shall mention also the following, 1st, for the topography of the whole nervous system, A. Monro, An. of the human bones, nerves, and lacteal sac and duct, Edinburgh, 1732, 1750, 1777. — Id., Nervorum an. contracta lat. reddita a Coopmans , Franeker, 1754. — R. Martin, Institutiones neurologicœ sive de nervis corporis humani tractatio, Stockholm, 1781. — J. G. Haase, Cerebri ncrvorumque corporis humani anatome repeiita, Leipsic, 1781. — D. E. Gunther, Cerebri et nervorum distribulionis expositio , Duisburg, 1786. — G. Coopmans, Neurologia c. obs. de calcula ex urethra extracto, Franeker, 1795. — 2d. Topography of the whole central portion or of some of its parts; N. Steno, Discours sur Vanat. du cerveau, Paris, 1679. — H. Ridley, Anatom y of the brain, London, 1695. — V. Malacarne, Nuova esposizione delta vera struttura del cervcletto umano, Turin, 1776. — S. T. Scemmerring, Debasi encephali et originibus nervorum e cranio egredientium, Gottingen, 1788.— V. Malacarne, Encefalotomia nuova universale , Turin, 1780. — Scemmerring, Vom Hirn und Rückenmarck, Mayence, 1788. — Malacarne, Neuro-encefalotomia, Pavia, 1791, 1798. — Sœrnmerring, Tabula haseos encephali, Francfort, 1799. — Chaussier, Exposition sommaire de la struct et des diff. parities de V encephale, Paris, 1807. — Scemmerring, Acadcmicæ annotationes de cerebri administrationibus anatomicis vasorumque ejus habitu, in the Denkschriften der acad. zu München, 1809. — Rosenthal, Beytrag zur encephalotomie, Weimar, 1815. — C. L. Somme, Recherches sur V anatomie comparée du cerveau, Antwerp, 1824. — Rolando, Saggio sulla vera struttura del cervello, in the Dizionario periodico di medicina, Turin, 1822, &c. Ludwig, Scriptores neurolugici minores selecti, Leipsic, 1791, 1795. — In describing each part of the nervous system we shall mention the authors who have treated of them specially.
collective term cerebrum ; but the term cerebro spinal axis is better. It
bulges very much in its anterior or cephalic part, while, in its posterior
or spinal, it terminates in a rounded, long, and thin cord. In a full-developed man it does not weigh quite four pounds apothecaries’ weight.
Chapter I. Spinal Marrow
§ 1712. Of the central parts of the nervous system we ought to mention first the spinal marrow ( medulla spinalis , s. dorsalis, corda spinalis, Gordon, Cerebrum oblongaium, Collins, ( 1 ) Corps et extrémité inférieure du prolongement rachidien de V enctphale , Chaussier), because it is formed first in the animal series and in the fetus.
§ 1713. Anatomists are not agreed as to the. limits of the spinal marrow. Its lower extremity is well marked because the central portion of the nervous system there ceases ; but all authors do not agree in respect to its upper extremity. Some confine the term spinal marrow to that part of the nervous system within the vertebral column, so that, in their opinion, it terminates at the first cervical vertebra and at the origin of the first cervical nerve. Others, on the contrary, include also under this term the lowest part of the mass within the skull, the medulla oblongata. Some also add the annular protuberance, the cerebral peduncles, the thalami optici, and the corpora striata.
The last two methods seem to us incorrect, because the medulla oblongata differs much from the cord contained in the spinal manow, not only in its size but also in its structure and situation, the arrangement and the distribution of its nerves ; and because in all these respects it resembles the rest of the mass lodged in the skull. As to the second, the only arguments in its favor are, that the spinal marrow continues uninterruptedly with the medulla oblongata, and that the annular protuberance seems to establish the boundary between this and the rest of the mass in the skull. But these two circumstances prove nothing, because the anterior cords of the spinal marrow are also uninterruptedly continuous with the cerebrum across the annular protuberance, and the posterior are also continuous with the cerebellum, on the outside of this protuberance, so that if we did not regard more essential differences there would be no separation between the cerebellum and the spinal marow, as the asserters of the third opinion mentioned above maintain.
(1) Rolando, Ricerehe anatomiche sulla struttura del midolla spinale, Turin, 1824. Ollivier, Essai sur l'anatomie et les vices de con formation de la moelle epiniere chez l’homme, Paris, 1823. — Racchetti, Della struttura della midolla spinale, Milan, 1816.
I. EXTERNAL FORM.
§ 1714. Generally considered, the spinal marrow is cylindrical ; it is however a little broader fiorn one side to another than from before backward, and thus in the first direction it appears slightly flattened. It may be divided into a cervical and a thoracic part, according to the regions of the vertebral column it occupies ; in its extent from one extremity to the other it has several prominences.
The first is seen at the upper part of the neck, where the cord becomes a little broader. Its breadth is seven lines in this place, while above it is a little less than six lines. Its thickness from before backward, far from increasing, often sensibly diminishes, and is not quite half an inch.
The upper or cervical prominence extends from the lower extremity of the cervical portion to the upper extremity of the thoracic portion, where it suddenly stops. Its length is a little more than three inches, and occupies the space between the second cervical and the first dorsal nerve. It is broadest near the fifth cervical nerve. The middle region of the thoracic portion of the spinal marrow again contracts. It is a little thinner than the cervical portion above the upper prominence.
The spinal marrow forms, near its lower extremity, a second prominence, called the inferior or the lumbar , which is never as large as the upper, and which extends from the first lumbar to the third sacral nerve. This projection is two inches long and five lines broad. It gradually becomes thinner and terminates in a blunt point. This blunt extremity is generally single, sometimes it is evidently bifurcated, and presents a superficial transverse fissure from whence a tubercle arises.
After leaving this point, which corresponds to the first lumbar vertebra, the nervous substance diminishes : and at the extremity of the vertebral canal, the spinal marrow appears only as a rounded filament, a little larger above than below, not quite one line thick in its whole extent, and is formed by the pia-mater. This filament which may be divided into several longitudinal fibres, descends between the origins of the nerves of the lower extremities, concealed by them, and extends to the lower extremity of the spinal canal, where it is attached to the duramater.
Hence it follows that the nervous substance of the spinal marrow, or the proper spinal marrow, by no means fills the whole vertebral canal, and occupies only about two thirds of it, the cervical and the thoracic portions being to the lower portion of the vertebral column as 2:1. The spinal marrow is also smaller than the vertebral canal in its othertwo dimensions.
Its anterior and posterior faces present a longitudinal groove as far as the medullary substance extends ; this corresponds to the median line, and is the anterior and the posterior median groove ( scissurce medulla spinalis mediana anterior et posterior ), which divides this part into two symmetrical halves, a right and a left These two
grooves are extremely narrow, and anatomists differ in respect to their existence and proportional depth.
Some, particularly Haller, assert that the posterior is never or seldom found; Chaussier says expressly that the anterior groove is at least deeper and broader than the posterior ; others, as Blasius, Petit, Vicq-d’Azyr, Gall, and Carus, say that the posterior is deeper than the anterior, which Vicq-d’Azyr and Carus think is the broader.
Others, Gordon for instance,(l) mention no difference between the two grooves. Bichat also expresses himself vaguely, for he only says that the two lateral halves are very distinct particularly anteriorly.
We have .always observed an anterior and a posterior groove, the latter generally very narrow, and rarely deeper than the other, although neither penetrates to the centre of the spinal marrow and to its gray substance. When the posterior seems deeper than the anterior, we have several times found that it was enlarged during dissection, so that adopting the opinion of several correct anatomists-, our predecessors, we believe the anterior groove to be larger in every direction than the posterior. The latter is much more perceptible in the prominences, particularly the lower, than in rhe rest of the spinal marrow.
Besides the median groove we observe also, on each side, but not exactly between the first two, and a little nearer the posterior than the anterior, a more superficial groove, which proceed obliquely inward and forward, and are called the lateral grooves ( fissura laterales). These two grooves proceed then to meet each other and the posterior, whence each lateral portion of the spinal marrow is also divided into two other halves, an anterior and a posterior, the former being much the larger. But these grooves are generally only simple depressions, or are at least more superficial than the preceding We cannot trace them the whole length of the spinal marrow, and they are seen only in the upper region of its thoracic portion. They separate on each side, the most posterior part of the circumference of the spinal cord from the rest of this circumference, not far from the posterior median groove. They not only converge inward and forward, but also downward, in the longitudinal direction of the spinal marrow, until they finally unite at the summit of its thoracic portion.
These lateral grooves are much more distinct in the early periods of life, than at a later period, when they frequently disappear and leave not the least trace.
We must distinguish them from the other two lateral grooves, the anterior and the -posterior ( sulci laterales anterior et posterior) which exist on each side, the whole length of the spinal marrow, and which are much broader than the preceding. These grooves receive the roots of the spinal nerves; thus they include numerous small depressions, situated after each other, from above downward, and into which the branches of the nerves penetrate.
(1) Mem. de Paris, 1781, p. 599.
The posterior is larger than the anterior.(l) It seems to be a real fissure, more than a simple groove, since it penetrates internally as a very thin wrinkle, in the same direction as the lateral groove described above, and meets that of the corresponding side. This posterior groove not only receives the posterior roots of the spinal nerves, but also marks the limit between the anterior and the posterior medullary cords, into which each half of the spinal marrow is divided, and which slightly project upon the surface of the spinal cord, which is otherwise rounded.
II. STRUCTURE OF THE SPINAL MARROW.
§ 1715. We have already described (vol. 1) the intimate texture of the spinal marrow ; we then have only to state in what manner the gray and the white substances are united, and the arrangement of the large division of these substances.
I. SUBSTANCES OF THE SPINAL MARROW.
§ 1716. The spinal marrow is composed of a gray and of a white substance, the first of which is every where surrounded by the second, and forms a nucleus which this latter envelops on all parts, or at least in most of its circumference.
These two substances differ in form. The gray is composed of a cent’ al transverse portion, and of two lateral parts, which send a penniform prolongation forward and backward. Each prolongation is arched, concave outward, convex inward, much thicker and blunter before than behind, where, except in the lumbar projection, which is almost as thick at its posterior part as in the anterior, it terminates in a point which is particularly evident in some subjects. It terminates loosely at the circumference of the spinal marrow, although it is not covered by the white substance, while the latter envelops its anterior extremity.
These penniform prolongations very probably, have intimate relations with the origin of the spinal nerves ; for the posterior extends exactly in the groove whence the posterior series of their roots arise, and the anterior also goes towards the anterior groove.
The white substance is arranged in an opposite direction from the grey, is convex externally and internally, and the gray nucleus is lodged in it as in a cavity. It is much thicker on its sides than in its other parts. Its right and left portions are not united forward except by a thin layer, which, however, exists through all the spinal marrow, and separates the anterior groove from the gray nucleus. Vicqd’Azyr(2) asserts that they are not united at all posteriorly ; he thinks that the posterior groove penetrates to the gray nucleus ; but they in fact appear to us to be connected by rather a thick medullary
(1) Loc. cit., p. 177.
(2) 7/OC. cit., p. 600.
layer, the existence of which is proved by dissection and by the analog}' of the brain.
The proportional quantity of the gray substance is not the same in all parts of the spinal marrow. There is more of it, at the lower than at the upper part of the cord. In the full grown fetus the lower part of the spinal marrow is frequently formed entirely of this gray substance, while in the rest of it a very distinct line of demarkation is already drawn between this and the medullary substance. Not unfrequently the gray substance in the adult is brighter, and the white browner than usual, and thus the texture of the medulla oblongata is more uniform than that of the rest of the central mass.
II. ARRANGEMENT OF THE GREAT DIVISIONS OF THE SPINAL MARROW.
§ 1717. The spinal marrow is composed in all parts of two lateral halves, or of two cords, which are fitted to each other, separated by two median grooves in most of their thickness, but united in the centre by the tranverse portion of the nucleus (§ 1716), backward and forward by the transverse layers of the white substance (§ 1718).
Each of these two lateral cords is formed of two halves ; an anterior which is much the larger, the form of which is that of a figure of 8 inverted ( oo ), and a posterior, which is much smaller and prismatic. The latter passes a little beyond the anterior posteriorly ; its base looks outward, and its summit inward.
Those two portions are separated by the posterior prolongation of the gray nucleus, and by the posterior lateral groove. The posterior cords are not only thinner and narrower than the anterior; they are also a little shorter, but not by any means in the same proportion. The lower extremity of the spinal marrow is formed entirely by the anterior, so that, seen from the side, it appears much lower in this place than in the rest of its extent.
Farther, each posterior cord is likewise composed of two portions, an external, which is larger, and an internal smaller, which are separated by a superficial but very distinct groove. Although this arrangement is also observed in the adult, it is much more evident in the early periods of life, and in animals, during their whole existence.
Most anatomists admit that the spinal marrow is composed of two lateral halves. Asch,(l) Monro, (2) and Sœmmerring,(3) have described the two cords which form it more or less minutely, the anterior which is larger, and the posterior which is smaller. Chaussier(4) even admits three on each side : he places the anterior and the posterior between the two median grooves and the anterior and posterior lateral grooves and the middle cord between the latter.(l)
(1) De prima pare nervorum ; in Ludwig, vol. i. p. 238.
(2) Ueber das Nervensystem, p. 22.
(3) Nervenlehre, p. 59.
(4) Loc. cit., p. 148.
§ 1718. The large lateral cords of the spinal marrow, are fitted to
each other in all their length, separated by the median grooves, but again
united and blended in the centre. This central part may be termed the
anterior and posterior medullary commissures , and the median or cortical commissure.
Gall thinks that the anterior and posterior medullary commissures differ, the first being composed only on the two sides of longitudinal fasciculi, placed side by side, while the second presents on both sides transverse slips, which exactly fit into each other. As yet we have not been able to satisfy ourselves of these two arrangements.
The posterior cords remain on the same side in all their extent. The anterior, on the contrary, intercross at the upper extremity of the spinal marrow, and those of the right side pass to the left, and those of the left side to the right, and all cross obliquely in this place. This decussation which is about five lines long, is indicated on the posterior face, where the anterior fissure does not exist in all its extent, and gives place to a broad but very superficial depression, to reappear immediately, and even deeper than before on the medulla oblongata. It becomes still more apparent on its anterior face, when we carefully separate the spinal marrow transversely in this place. The two cords do not intercross, but pass in a mass from one side to the other : they divide into from three to five fasciculi, which pass some above the others, like the fingers when the hands are clasped. The anterior cords however, do not wholly cross ; their anterior and their posterior parts only present this arrangement. We may easily be convinced of this by a transverse section of the spinal marrow in this place : it is then very manifest, that a white medullary band is detached on each side from the posterior extremity of the anterior cord, which goes forward and inward; and intercrosses with that of the side opposite, while the lateral parts continue their progress from below upward uninterruptedly. By this decussation, the anterior part of the gray nucleus of the spinal marrow, is divided into two lateral portions, each comprised between the internal face of the decussation, and the external lateral portion of the anterior medullary cord.
(1) Gall {loc. cit., p. 115) and Chaussier (Joe. cit., p. 148) assert that Highmore mentions each half of the spinal marrow as composed of four cords, and consequently
that the whole number of these last is eight. It would seem that Gall repeated the
assertion after Chaussier, but we find nothing to justify it in the passage referred to
by the Paris professor (Anat. b. iii. p. 1. chap, viii.) and Linden also quoted by
Chaussier, says nothing like it. Although Chaussier rejects Highmore’s opinion, it
is not however contemptible, since by uniting Chaussier’s description and our own,
we arrive at the same conclusion.
But we have never found that the anterior internal part of the anterior cords of the spinal marrow which produce the pyramidal bodies of the medulla oblongata, remains on the same side, and that the intercrossing was confined to the fasciculi which proceed from the posterior part of this cord to the medulla oblongata. (1) If it was thus the decussation would not be visible externally : the anterior part would continue uninterruptedly to proceed externally along the same side of the bodj r , and would receive the fibres from the posterior part of the cord on the other side only very deeply, but this is never seen.
This decussation is so evident, that we can hardly conceive of its being doubted by several anatomists, as Sabatier, (2) Vicq-D’Azyr,(3) Chaussier,(4) and Gordon(5). Gordon states that he does not speak of the two or three bands by which the anterior groove of the spinal marrow is interrupted at the union of the cervical with the cranial portion, except on account of the absurd theories with which physiologists have often connected it. But this decussation has been demonstrated since the time of Mistichelli,(6) by Petit, (7) who was the first to demonstrate it exactly: by Santorini, (8) by Vicq-D’Azyr,(9) with less of precision and clearness, (10) finally, it has been well described by Gall and Cuvier. It has been partly figured by Petit, Santorini, and Gall.
All the objections against its existence are refuted by a positive fact, that the particulars previously described in the whole spinal marrow, are observed only in the place mentioned, and are there constant.
But the cords of the spinal marrow intercross in no other place, and although the contrary has sometimes been maintained, (10) all other arrangements of the spinal cord which resemble these decussations, are only intended to unite the commissures.
The structure indicated by dissection, is demonstrated by the difference between the phenomena which occur when the central portion of the nervous system is injured either above or below the place we have mentioned.
§ 1719. The substance of the spinal marrow of man is solid, not only when it is perfectly devoloped, but even sometime after birth, although several writers have admitted a cavity within it. We may conclude this from the difference in the opinions of authors in regard to the situation and the size of this cavity. Stephanus mentions its existence only as a general fact, without telling where it is situated. (1 1) Morgagni asserts that it is placed in the centre of the spinal marrow, especially its upper part, where he has frequently found small longitudinal cavities entirely covered with gray substance, and where once even he found one which was very large, five fingers long.(l) Portal seems to have observed it in the same place : but once he found it comprised all the spinal marrow, and that it appeared to be covered with a very thin membrane : and another time it extended only to the fourth cervical vertebra. Gall, however, describes two canals existing all the length of the medulla, one on the right, the other on the left, which do not communicate with each other, or with the cerebral ventricles, but terminating in culs-de-sac, in the thalami optici, where they enlarge and produce a cavity the size of an almond, while the single and median cavity of the other writers is considered by them only as a prolongation of the fourth ventricle.
(1) Rosenthal, Beitrage zur Encephatotomie.
(2) Mêm. sur lamoelle del’epine et ses enveloppes ; in the Trait, d'anal., vol. iii. p. 452.
(3) Mém. de Paris, 1781, p. 598.
(4) Loc. cit., p. 143.
(5) Human anatomy , vol. i. p. 177.
(6) Dell ’ apoplcssia, Rome, 1709.
(7) Lettre d'un médecin, 1710, p. 11.
(8) Septemdecim tabul., p. 28-29, vol. ii.
(9) Loc. cit., p. 598.
(10) We instance Bartel’s opinion, who considers respiration as a motion dependent on the brain.
(11) De diss. part. corp. hum., b. iii. Paris, 1545, b. iii. c. xxxv. p. 341.
We have never found in man after birth, a median canal or two lateral canals. The circumstances under which they have been found by Gall and Portal, prove them to have been morbid. From Gall’s observations, it cannot be doubted that the canals he saw were produced ! by art, since he remarks that they could be demonstrated only by dividing the spinal marrow in such a manner that air might be introduced for six or eight lines. The smoothness and distinctness of the surfaces do not prove the real existence of the canals in question, for the first circumstance depends on the softness of the nervous substance, and the second on th ecentral prolongation of the pia-mater. We shall add one observation which we have always made, viz. that the ease with which these canals may be demonstrated, is in a direct ratio with the softness of the medulla oblongata ; and it is much more easy by continuing the inflation to make these communicate with the fourth ventricle, than to follow them into the thalami optici. We have succeeded, when the spinal marrow was soft, in pushing air into its whole length, without employing any cutting instrument, and without thinking that the existence of a normal cavity was proved by the space found in a soft and viscous mass, after having employed such a mode.
We discover only at the top of the spinal marrow, a rounded and extremely narrow canal, from six to nine lines long, terminating below by a cul-de-sac, and continuous above with the floor of the fourth ventricle.
III. WEIGHT OF THE SPINAL MARROW.
§ 1720. The absolute weight of the spinal marrrow, in the adult when deprived of its envelops, and entirely separated from its nerves, is more than an ounce. It is to the brain as 1 : 40.(2)
(1) Adv.anat., vi. anim. 14.
(2) Chaussier establishes a ratio more favorable to the spinal marrow, as he gives the proportion as 1 : 19-25, but this is evidently wrong-, doubtless because the origins of the nerves were not removed.
IV. CONSISTENCE OF THE SPINAL MARROW.
§ 1721 . It is generally thought that the spinal marrow is softer than the cerebrum. When, however, it is observed in the recent state, we remark, that although it is less consistent than some parts of the encephalon, particularly the annular protuberance, it is at least harder than the cerebrum and cerebellum. (1)
Chapter II. Encephalon
§ 1722. The encephalon ( enccphalwn ), or that part of the central portion of the nervous system contained in the skull, has a rounded and oblong form. It is composed of two parts, which differ in size and arrangement ; an inferior which forms its base, and a superior which extends upwards and on the sides. These two parts are however directly continuous with each other, and with the spinal marrow.
The upper part very naturally divides into two portions, the cerebrum and the cerebellum , which differ in respect to situation size and structure. But it is more difficult to establish divisions in the lower part, since the different segments which form it, pass into each other by less evident shades. Hence, also, the difference which exists between authors in regard to the extent of the parts embraced by the same name.
Thus the term medulla oblongata has been used to designate a greater or less segment of the lower part of the encephalon : but some give this name to all the parts which form the lower region of this viscus, while others apply it only to some of them, and are not agreed in respect to the number of the parts which are thus collecti vely designated.
Many have limited the meaning of the word still more, and employ it only to designate the lower part of the nervous substance, which extends from the occipital foramen to the annular protuberance. Such is, for instance, the method of Haller, Sœmmcrring, Cuvier, Chaussier and Bichat. Some of these anatomists, however, particularly Scemmerring, Bichat, and Chaussier, have considered the medulla oblongata not as a particular portion of the central mass of the nervous system, but only as the upper extremity of the spinal marrow, as we have already remarked.
The middle region of the encephalon is situated in front of this part, and is considered by some writers, as Chaussier and Bichat, as a special segment of this mass, called the cerebral protuberance ( protuberantia cerebralis ) by Bichat, and the mesocephalum by Chaussier.
But these two authors do not give it the same limits, for Chaussier
(1) Chaussier, p. 116. — Gordon, p. 182.
states it to be composed only of the annular protuberance, the tubercula quadrigemina, and of the valvula cerebralis, while Bichat includes in it also under the term prolongations , those medullary fasciculi which extend from the annular protuberance forward to the cerebrum, and backward to the cerebellum. Others, as Gordon, consider the annular protuberance as belonging to the cerebellum.(l) Vicq-d’Azyr had already said with more justice, that it must be described separately, and that it belongs neither to the cerebrum nor to the cerebellum.
ARTICLE FIRST. MEDULLA OBLONGATA.
§ 1723. The best mode, in our opinion, is to include under the term medulla oblongata , not only what Haller and his successors have so termed, but also the annular protuberance ; to insulate this part from the rest of the encephalon, and then to divide the remainder into two other portions, the cerebrum and the cerebellum. We also maintain this position, as the portion we include under this term still belongs in common to the cerebrum and cerebellum, while that which is found in front of it, belongs only to the cerebrum, and that which is behind it makes a part of the cerebellum. We also ground ourselves on the fact, that what Haller and others term the medulla oblongata, differs so much from the rest of the spinal marrow in respect to structure, that we must consider it separately(§ 1713).
The medulla oblongata , in our opinion, occupies all the length of the base of the skull, from the large occipital foramen, to the posterior edge of the sella-turcica. Its form is irregularly quadrilateral as it gradually enlarges from behind forward. It is continuous below with the upper extremity of the spinal marrow, anteriorly with the cerebrum, laterally and superiorly with the cerebellum. We must therefore consider it the point of union, or the focus of these three segments of the central portion of the nervous system.
The posterior and inferior part, the proper medulla oblongata of several writers, may perhaps be termed the rachidian bulb, as Chaussiez^) and Bartels(3) call it ; the anterior and upper will retain its usual name of annular protuberance.
I. RACHIDIAN BULB.
§ 1724. The rachidian bulb ( bulbus rachidicus, bidbus rachidicus superior , e. medulla oblongata, Haller, pars cephalica, s. extremum cephalicum , s. spinalis medullœ principium ) is the most posterior and the most inferior part of the encephalon, the direct continuation of the spinal marrow. It extends from the first cervical vertebra to the centre of the body of the basilar bone, and exactly fills the posterior part of the upper and concave face of this body.
(1) Loc. tit., p. 112.
(2) Loc. cit., p. 120.
(3) Vom. Athmen, p. 108.
It has the form of an elongated triangle, and swells insensibly from
behind forward, and from below upward. It generally does not exceed
an inch in length, and its greatest breadth is about eight lines.
I. EXTERNAL FORM.
A. LOWER PACE.
§ 1725. The lower face of the rachidian bulb is slightly convex, and divided by a groove two or three lines deep, into two halves, a right and a left, which is continuous with the anterior groove of the medulla oblongata, from which, however, it is slightly separated by the decussation of the anterior cords. (§ 1718)
This inferior face presents two pairs of eminences, the pyramids and the olivary bodies.
a. Of the pyramids.
§ 1726. The pyramids (eminentiœ, s. corpora pyramidalia, s. corpora pyramidalia antic a . , s. eminentiœ oblongœ, Gordon, medianœ internes ) are visible with the intercrossing of the anterior cords of the spinal marrow (§ 1718), and are situated entirely inward, so that their internal faces touch. They occupy the whole length of the medulla oblongata. They are from about two and a half to three lines broad. They gradually become broader from below upward, and at the same time their upper projects more than their lower part. They terminate anteriorly by a contracted and rounded extremity, at the posterior edge of the annular protuberance, which projects downward and forward much beyond it. At the same time, they separate slightly from each other, so as to leave in the median line, between them and the posterior edge of the protuberance, a small liiangular hollow, into which the pia-mater penetrates. The anterior groove of the spinal marrow extends between the two pyramids, and becomes deeper at their upper part. Although these eminences terminate as such at the annular protuberance, they how T ever pass uninterruptedly through it, and go forward.
There is no decussation above the point we have already mentioned (§ 1718). The pyramids are also separated from each other by the anterior groove, in the rest of their length, always excepting the place directly below their upper extremity, where they are reunited by a small transverse medullary commissure, about a line and a half high. This reunion occurs at least frequently, just before they separate from each other, as if in this place their substance was pressed forward.
Prochaska asserts(l) that there is no gray substance within them : we have succeeded no better than Vicq-d’Azyr(2) in finding it.
In passing from below upward, they send off filaments which are entwined around the olivary bodies.(3)
b. Olivary bodies.
§ 1727. The olivary bodies , the olivary eminences , the lateral eminences ( olivœ, s. eminentiœ olivares, Vieussens, s. laterales , Chaussier, s. ovales, Sœmmerring, Gordon), are situated on the outside of the pyramids. They go a little obliquely from below upward, and from behind forward, and form a rounded very elongated prominence, the largest diameter of which is from above downward. The prominence which disappears gradually above and below, passes from the lower face to the lateral face of the medulla oblongata, and is about seven lines long, two and a half broad, and one high. The olivary eminences do not extend so high as the pyramids : they cease about a line below the posterior edge of the annular protuberance.
The roots of the hypoglossal nerve arise from the groove between them and the pyramids.
These eminences are medullary externally, but the thin layer of white substance which covers them, is easily raised, and we then perceive a solid gray elongated nucleus, surrounded by an uneven and serrated edge, the centre of which is white, and the circumference of a deep gray. This nucleus is always loosely imbedded in medullary substance, and is called the corpus fimbriatum ( corpus olivœ fimbriatum, s. denticulatum , s. rhomboideum). When cut longitudinally, tranversely, or horizontally, we see very evidently that the gray border of the olivary bodies is interrupted inward, and consequently that the white substance which they inclose, is continuous on this side with the pyramids. This gray edge, on the contrary, unites below with the gray substance of the spinal marrow. From the place of decussation, and even by this decussation, the gray nucleus of the spinal marrow is divided anteriorly into two halves (§ 1718). The olivary bodies seem to be only a development of this arrangement. In fact, new medullary substance develops itself in the gray substance as the spinal marrow enlarges in this place, and is continuous internally with the pyramids. It perhaps would be more correct to say that the latter enlarges outwardly, and that it penetrates into the gray substance in the same manner as the two halves of the spinal marrow separate from each other on the two sides, before it enters the skull, and are enveloped by the gray substance.
(1) Destmct. ner i\, Vienna, 1779. — Gpp. min. vol.i. p. 373.
(2) Mem. de Paris, 1781, p.587.
(3) Santorini, Septemd, tab., p. 26 — 27.
B. LATERAL FACES.
§ 1728. Thetwo lateral faces of the medulla oblongata, are sloped and slightly convex outward. They are formed by a medullaiy projection situated outward and backward before the olivary bodies, which goes from below upward, and from within outward, and arrives at the cerebellum. This projection is called the lateral pyramid , the restiform body, the crus of the cerebellum, the posterior eminence, the peduncle of the spinal marrow ( eminentia pyramidalis lateralis, Tarin ; corpus, s. processus restiformis, Ridley ; crus cerebelli ad medullam oblongatam, eminentia posterior, Chaussier; pedunculvs medullœ spinalis, Gordon). Those of the two sides unite at their inferior internal extremity. Each of them is a prolongation of the posterior cord of the spinal marrow at its side. Where they unite, they project slightly inward. They separate from each other from below upward, from behind forward, and from within outward.
A thin medullary layer about three lines long, and less than three broad, leaves the back part of the upper edge of the restiform body on each side; this goes inward. These two layers are separated by the pia-mater, which passes from the restiform body of one side, to that of the other, but they never unite in a state of perfect development. They may be termed the small bridges of the rhomboidal sinus(§ 1729), and may be considered as indicating the union of the two posterior cords. A second and larger, and particularly thicker medullary prolongation, arises from the anterior part of the restiform body, and is covered by the root of the pneumo-gastric and hyoglossal nerves, and is attached to the choroid plexus of the fourth ventricle.
C. UPPER FACE OR CALAMUS SCRIPTORIUS.
§ 1729. The lateral face is imperceptibly continuous with the upper face, by means of the restiform body. This upper face is very much grooved at its anterior and larger part, and these present a triangular depression, which terminates in a point, and is called the rhomboidal sinus, the sinus of the medulla oblongata, the ventricle of Jlrantius, the fossa of the fourth ventricle, the triangular fossa the calamus scriptorius, (sinus rhomboideus, sinus bulbi rachidici, veniricidus Jlrantii,foveola ventriculi quarti, Chaussier ; fossa triangularis, Gordon) . This depression extends more or less into the upper extremity of the spinal marrow, where it gradually contracts to a considerable degree.
On the superior face of the medulla oblongata, directly at the side of the median depression, we observe two medullary cords, which gradually enlarge from behind forward, and are only the upper face of the anterior cords of the spinal marrow, which traverse the spinal marrow from below upward. Between them and the restiform bodies is a broader layer of gray substance.
a. Medullary striae of the upper face.
§ 1730. Near the anterior extremity of the upper face, we constantly observe white striæ,(l) which go from within outward, usually project a little, and generally extend from the median depression to the outer part of the face, but which vary in respect to their existence, number, volume, progress, and direction.
1st. Existence. They are, in fact, very constant : but they are sometimes deficient on one or even on both sides. We have never seen a case of the latter, but the former we have met with twice, and always on the left side. Prochaska(2) and Wenzel(3) have seen both.
2d. Volume. They vary in respect to the three dimensions. Sometimes they are extremely narrow from above downward, almost capillary, and at the same time single. In other cases they form considerable striæ, which are more than two lines broad. Sometimes, also, they are very thin, and do not pass beyond the inferior face of the rhomboidal sinus, and do not penetrate into it. They not unfrequently form a rounded projection above this same face, and penetrate more or less into the medulla oblongata, so as to arrive at its lower face. Finally their length varies much. Generally, but not always, some or all of them extend outward to the auditory nerve, and usually go inward to the median groove : but sometimes also they proceed beyond this groove, and blend with those of the opposite side. Not unfrequently they do not extend to it. We have generally remarked, that when they are large and numerous, they usually unite in part or entirely, on the median line.
3d. Number. Then number varies sometimes ; it is independently of their size, and most generally is inversely as the latter, from one only to fourteen.
4th. JLri'angement. The strife of one side generally interlace differently together.(4) They are however sometimes entirely distinct.
5th. Direction. Their direction, most generally, is more or less transverse, although a little oblique from behind forward. Sometimes they proceed almost directly forward. All, or at least some of these striae, most generally extend to the auditory nerve, as we have already stated, and very evidently form the most internal part of its origin.
Very commonly also, the anterior which compose the smallest part of the mass, go obliquely farther forward and outward towards the trifacial nerve, although we cannot clearly demonstrate any connection between them and this nerve. The posterior are sometimes attached to the filaments of the root of the pneumogastric nerve.
They frequently vary in a most striking manner, in every respect, on both sides of the body in the same subject.
(1) Prochaska De struct, nerv., Vienna, 1779.— Wenzel, De penit. struct, cerebri , ch. xxiii.
(2) Doc. cit., p- 388.
(3) Loc.cit. p. 171.
(4) Wenzel, toe. cit.. p. 173— We have seen this several times.
These striae are very probably not only the roots' of the auditory nerve, but are connected, although less evidently, both with the trifacial and with the pneumogastric nerve, of which we shall speak more fully, when endeavoring to establish a fewer number of cerebral nerves than is generally admitted.
b. Gray bands of the upper face
§ 1731. Before the white striae, we see on the upper face of the medulla oblongata, other larger and slightly elevated striæ,( 1 ) which arise at some distance outside of the median line, so that their internal extremities are never blended. These striae extend from within outward, gradually swell, are convex forward, and pass over the anterior part of the posterior pyramids. They always unite with the auditory nerve at their external extremity, and are very constant : for of ninetyseven cases they were deficient in only two. (2) They are called the gray bands ( fasciolœ cinerea). They are also generally much marked, and are similar on both sides: but sometimes, although very rarely, those of the two sides are dissimilar, or they are scarcely perceptible on either : this peculiarity depends neither on the age nor on the sex. They arise generally by one, and rarely by two roots, and are always single on each side. Their intimate connection with the auditory nerve, is proved by the fact that it disappears in deaf people.
II. TEXTURE.
§ 1732. The cords of the spinal marrow enlarge in the medulla oblongata, and divide there into fasciculi, more evidently than in the spinal marrow. At the same time, the posterior separate from below upward, and distinct bodies, the olivary bodies , are developed in the substance of the anterior, which are unconnected with the organization of the spinal marrow.
The anterior cords of the spinal marrow, divide evidently into at least two halves, an anterior which is smaller, and a posterior which is larger. Of these two halves, the anterior cross and form the pyramids (§ 1726), the posterior ascend behind the olivary bodies, enlarge and form the floor of the calamus scriptorius, and of the fourth ventricle. We also find another smaller fasciculus, which Gall asserts, is not constant, which Rosenthal has described more exactly, (3) and which our dissections have shown to be constant. This middle fasciculus, which touches the olivary bodies, surrounds them and passes through the annular protuberance to go forward into the tubercula quadrigenina.
(1) The merit of having 1 2 3 made profound researches on these striae belongs to Wenzel, but he neither discovered their existence nor constancy, nor their connection with the auditory nerve, since all these facts are already mentioned positively by Prochaska. (loc. cit. p. 387-391.)
(2) Wenzel, loc. cit. p. 184.
(3) Beytrœge, p. 24—27.
The division of the posterior cords of the spinal marrow into two
fasciculi (§ 1717) is still more evidentin the restiform bodies, on account
of their enlargement. The internal, which are smaller, swell at the
lower extremity of the calamus scriptorius, but disappear in a point
before the restiform bodies have terminated their course towards the
cerebellum.
II. ANNULAR PROTUBERANCE.
I. EXTERNAL FORM.
§ 1733. The annular protuberance, called also the bridge of Varolius (nodus cerebri, pons Varolii, emineniia, s. protuberantia annularis, protuberantia encephalica, commissura cerebri ), is a considerable and somewhat regularly quadrilateral eminence, extending however rather more from right to left than from before backward ; it is observed on the lower face of the cerebrum, projects more than three lines above the lower face of the medulla oblongata and the cerebral peduncles, gradually becomes thicker on each side near its centre, and is separated from the medulla oblongata and the cerebral peduncles, by very distinct limits. Its greatest length is one inch, its greatest breadth is one inch and some lines, and its greatest height, at its anterior extremity, is nearly one inch. Its anterior and posterior edges are convex on the sides, and concave in the centre, the anterior more so than the posterior. A superficial, but very evident groove, extends all along its inferior face from before backward ; this is continuous with the serrated portion of the anterior and of the posterior edge. On the sides, the annular protuberance imperfectly divides internally into two halves, one of which is turned toward the tubercula quadrigemina, the other up towards the cerebellum, and both turn around the posterior crura of the cerebellum.
II. TEXTUBE.
§ 1734. The annular protuberance is formed externally of white
fibres, transverse and convex forward, of which the central and the anterior particularly incline very much backward, towards the cerebellum.
It is very firm, and the firmest part of the centre of the nervous system.
On examining it internally, which must be doneby horizontal, transverse,
longitudinal, and even by perpendicular incisions, a little oblique from
within outward, and from behind forward, we remark that its texture
is very complex.
Immediately below the external medullary layer, we discover a grayish substance. This substance is not pure : it alternates the whole length of the protuberance with transverse and very numerous bands of medullary substance, which are thin and convex inward, and are attached to the external.
About two lines above the lower face of the protuberance, we observe
on each side, almost in the centre of each lateral half, insulated longitudinal medullary fibres, which are directed from within outward, and
from behind forward, and alternate with the transverse fibres. They
are convex below, and concave above. They form a fasciculus, about
four lines high, which contains in its centre only white substance,
through which the cortical substance passes upward and downward.
This fasciculus is the direct continuation of the pyramids. It continues uninterruptedly forward with the lower face of the cerebral peduncles.
Next comes always from below upward, a very thick layer of gray substance, interrupted by perpendicular layers of medullary substance, situated some behind the others; then, on this layer is another which is thinner, of longitudinal medullary striae, convex above, concave below, which arise behind the upper fasciculus of the anterior medullary cords of the medulla oblongata, pass above the central gray layer, blend forward with the lower and thickest layer of medullary substance, and thus arrive upon the upper face of the cerebral peduncles.
Consequently the upper and lower fasciculi which result from the division of the anterior cords of the medulla oblongata, again unite at their anterior part, in the annular protuberance.
The number of the longitudinal striae, especially the inferior, diminishes much from without inward. They are separated from each other, upward and downward, by gray substance, and disappear entirely at about the centre of the annular protuberance.
The central part is formed of gray and of white substance ; it is much higher in this place, and only some longitudinal medullary striae pass above it.
Thus the anterior medullary cords not only increase in size and divide in their course across the annular protuberance, but they are still directed from within outward.
III. WEIGHT OF THE MEDULLA OBLONGATA.
§ 1735. The entire medulla oblongata generally weighs a little more than half an ounce. Its weight then is to that of the spinal marrow, as 1 : 2 ; to that of the cerebellum as 1 : 1 0 ; to that of the cerebrum as 1:74: finally to that of the whole central mass as 1 : 86.
The rachidian bulb weighs three drachms ; the annular protuberance one.
ARTICLE SECOND. CEREBELLUM.
I. EXTERNAL FORM.
§ 1736. The cerebellum ( cerebellum , s. parencephalis){\) is situated below the posterior part of the posterior lobe of the cerebrum, from which it is separated by the tentorium, and occupies the inferior fossæ of the squamous portion of the occipital bone. We may divide it into the body and crura, and the body comprises the lateral parts, and a centre.
§ 1737. The body of the cerebellum has a rounded and oblong form. Its greatest breadth, which is from side to side, is about four inches. It is about two and a half inches from before backward in its broadest portion : it is two and a half inches from above downward in its centre, and only half an inch at its edges ; in approaching which, it gradually becomes thinner, so that it seems a little flattened in the latter direction. Considered generally, it is circumscribed by two slightly convex faces, an upper and a lower, and by four obtuse edges, distinguished into anterior, lateral, and posterior. The upper face is sloped like a roof, that is, it projects most at its central part, whence it descends almost flat to the edges, backward, outward, and forward, although a little less in the latter direction. The inferior face, on the contrary, is concave from before backward, at its centre, so that the anterior and the posterior parts of this groove form the greatest hollow.
The two faces are separated by a groove an inch deep in most of its extent, which corresponds to the posterior edge, and thence goes inward. This is called the large or the horizontal groove of the cerebellum ( sidcus cerebralis magnus, Vicq-d’Azyr ; sulcus magnus horizontalis, Reil). This groove divides the cerebellum into an upper and a lower half, besides the two lateral halves into which it is divided by the median longitudinal groove.
The anterior edge is the shortest, and is rendered very concave by a broad depression. The two lateral edges are straight, longer than the anterior, and oblique from before backward, and from within outward. They are continuous with the posterior, where the cerebellum is broader between their posterior extremities. The posterior edge is the longest, and is composed of two very convex lateral halves, which are separated by a median groove, about four lines deep and three broad. This groove is continuous with the median depression of the lower face. Thus the cerebellum is narrower in the centre than in the rest of its extent, and is divided by the anterior and posterior depressions of the edges, and by that of the lower face into two halves, called very improperly, the hemispheres ( hemisphœrœ cerebeUi). Each of these hemispheres has an irregularly quadrilateral form. The outer face of the cerebellum is not smooth. We observe in it numerous slight elevations, formed by the upper face of the layers (lamincc). These elevations are convex externally, concave internally, and go unevenly from before backward, being separated by grooves, into which the pia- mater descends. These layers are not single, but they frequently subdivide and interlace, and are adapted to each other very exactly, even externally. The depth of the grooves, and consequently the height of the layers, are not every where the same. In the place where the grooves are very deep and very long, and where also the adjacent layers are entirely separated from each other, the cerebellum is perfectly divided into several segments, which are called lobes ( lobi ).
(1) Rolando, Osservazioni sul cerveletto, in the Memoria della reale academia,
della scienza di Torino, vol. xxix. p. 163.
The best mode of describing the form of the cerebellum, is to examine separately its lateral parts and its centre.
I. LATERAL PARTS.
§ 1738. The two faces of the cerebellum, the upper and the lower, are divided very constantly by deep grooves into several lobes, which are superior and inferior.
I. UPPER LOBES.
§ 1739. The two lobes of the upper half of the cerebellum, are the upper anterior and the upper posterior.
1st. The upper anterior or square lobe ( lobus anterior , superior , s. quadrangularis ) is irregularly quadrilateral, and narrower forward and outward than backward and inward. It is continuous with that of the opposite side by a central part which is not contracted, and is the highest point of the cerebellum. The two united lobes have a semicircular form. Their posterior edge is convex and sharp, and is turned backward with the posterior face, while the anterior, which is concave, and which forms at the same time the anterior edge of the cerebellum considered as a whole looks forward. The blunt extremity which forms the anterior half of the lateral edge of -the cerebellum, looks forward and outward.
This lobe is separated from the upper posterior by a very deep groove, the superior groove of the cerebellum (sulcus superior cerebeUi , Vicq-d’Azyr).
2d. The upper posterior or semilunar lobe , lobe semi-lunaire ( lobus superior posterior , s. semi-lunaris) , comes immediately next the preceding. It forms the posterior and external part of the upper half of each hemisphere. It is semilunar, thicker and broader forward than backward ; separated backward from the lower posterior by the large lateral groove, and forward from the upper anterior by the upper groove : it is attached inward to the synonymous lobe of the other hemisphere by a thinner and more sloping part, formed of white substance, called the commissure of the upper posterior lobes. The considerable groove between the two upper posterior lobes, forms the commencement of the lower posterior median groove.
II. INFERIOR LOBES.
§ 1740. There are four inferior lobes.
1st. The posterior or inferior semilunar lobe ( posterior inferior, s. semi-lunaris), forms the posterior superior and external part of the lower half of each hemisphere. It is separated from the superior and anterior by the large groove, (§ 1737) and from the next by the inferior external groove ( sulcus inferior externus ), which is very deep. It is divided by two considerable but more superficial grooves, into three concentric portions -which follow one another from behind forward, and diminish in size in the same direction.
The two lateral halves are connected by a narrow and slanting commissure, with which the middle of these three lobes is directly continuous, while the anterior and the posterior only touch on its sides.
The most internal segment has been considered a special lobe, and termed the small or thhi lobe ;(1) but this distinction seems to us inconvenient, because we might just as well consider the middle and anterior segments as so many distinct lobes.
2d. The inferior anterior lobe , the cuneiform or internal inferior or digastric lobe ( anterior inferior, s. cuneiformis, s. biventer), is much smaller. It is composed of layers, which proceed almost directly from before backward. It is broader and thicker forward and outward than it is inward, where it at first contracts very much, and then terminates together with the third segment of the preceding lobe, in a very bulging central part.
3d. The third inferior lobe, the lobe of the medulla oblongata, the spinal lobe, the monticule ( lobus inferior internus , ionsilla , Malacarne ; s. lobulus medullæ oblongata, s. monticulus, Vicq-d’Azyr; lobus spinalis, Gordon), is smaller than the preceding, and is composed of layers which proceed directly from before backward, and is convex both out(ward and inward. Its anterior extremity rests in the restiform body of the spinal marrow. (§ 1728) Posteriorly it gives origin to the uvula, which is inserted between the two amygdalae.
4th. The fourth inferior lobe, the lobe of the pneumo gastric nerve ( flocctdus , s. lobus nervi pneumogastrici, Vicq-d’Azyr, lobus subpeduncularis, Gordon), arises a little above and before the preceding, from the posterior edge of the peduncle which goes from the cerebellum to the tubercula quadrigemina, directly where this peduncle unites with that which extends from the cerebellum to the medulla oblongata. It arises in this place from a thin pedicle, descends between the auditory and pneumogastric nerves, and goes forward downward and outward. Almost all of its medullary nucleus is exposed forward and backward, fimbriated in its whole extent outward, and only in its lower part inward, and is covered both outward and inward with gray layers.
(1) Malecarne, and Reil, loc. cit., p. 13.
The direction of this segment of the cerebellum, is precisely the opposite of that of the others ; it is also the loosest.
The two lobes become, upward and inward, a broad semicircular medullary lajmr, which rises above on the nodule, and is loose posteriorly, called the posterior medulary vail ( velum medulläre posterius). This layer swells on its internal edge, into a thick mass of medullary substance, folded crosswise, and covered with cortical substance, which assists to form the posterior part of the fourth ventricle.
II. CENTRAL PORTION.
§ 1741. Although, strictly speaking, the central part of the cerebellum is no where separated from the two lateral parts, by a want of continuity in the substance ; it however differs a little from them in form.
The distinctive character of the formation of this central part is, that it is formed by transverse layers and plates, and that except in its middle posterior region, it presents a rounded form bulging from behind forward.
On its anterior face is the most superior part of the cerebrum. The anterior part of its lower face is also very much elevated, but the posterior is lower. Its lateral faces and its anterior part are situated in a large depression, the direction of which is from before backward, which separates the two hemispheres.
The middle region is usually termed the vermiform eminence (vermis cerebelli ), and it is divided into an upper and a lower part.
I. UPPER PART OF THE MIDDLE RFGION.
§ 1742. The upper part of the middle region extends from the middle of the posterior edge of the upper face, above the anterior edge to the tubercula quadrigemina.
It is composed of the upper or anterior vermiform process and the cerebral valve.
The upper vermiform process may also be divided into three portions:
1st. The commissure of the two upper posterior lobes.
2d. The larger upper part, or the monticule ( moniiculus cerebelli).
3d. The lower part which is much smaller, or the anterior vermiform process.
The commissure of the upper posterior lobes, is thin, narrow, and lower than the lobes it unites.
The monticule, which is the highest part of the cerebellum curves from behind forward, and from below upward, as high as the posterior edge of the tubercula quadrigemina. It is formed of five segments placed one after another from behind forwards, they become thicker from before backward, but the third is separated from the others by the deepest transverse grooves. These segments extend from the monticule into all the thickness of the hemispheres ; but they gradually contract in approaching the anterior edge, so that the monticule, especially on account of the rounded prominence in its centre, is almost three times as long, as are the lateral edges of the upper face of the cerebellum.
The lower smaller part, or the proper anterior vermiform process , has a direction the inverse of that of the monticule, that is, it proceeds from above downward, and from before backward. It is reflected near its posterior extremity at an acute angle, and is continuous with the cerebral valve, on which it rests directly its entire length.
II. CEREBRAL VALVE.
§ 1743. The cerebral valve, the large valve of the brain ( valvula cerebri, valvula magna, velum medulläre, velum medulläre anticum , pars anterior veli medullaris ), arises from the posterior extremity of the anterior vermiform process, and is attached on the sides to the inner face of the prolongations sent by the cerebellum to the tubercula quadrigemina, and terminates by its anterior extremity in the depression between the posterior pair of the tubercula quadrigemina. It contracts from behind forward, becomes thin, and terminates in a convex edge.
Its lower face is smooth. The upper presents posteriorly in nearly all its extent, transverse grooves, which generally extend only to the lateral edges ; it is frequently, but not always, divided by a slight longitudinal groove into two equal lateral parts. Its anterior part is much less extensive than the other, and smooth ; it is formed in its- greater and posterior part, of gray substance. It is also formed anteriorly, at least on its lower face by this substance ; we however usually find at its anterior extremity, or directly behind it, on the median line, a white band from one to two lines broad, convex posteriorly and narrower on the sides : it is terminated forward by a small point, which is attached to the groove between the two posterior tubercula quadrigemina. This band generally gives rise to some filaments of the fourth cerebral nerve, but goes mostly only in the upper edge of the anterior peduncle of the cerebellum, and disappears on its outer face.
III. LOWER PART OF THE MIDDLE REGION.
§ 1744. The lower part of the middle region of the cerebellum, commonly called the inferior vermiform process, is a little lower posteriorly than the posterior part of the two lower posterior lobes which it unites, although it is not so low as the commissure of the upper posterior lobes situated above it. It is formed of two halves, separated by a superficial transverse groove, and situated one above the other. It presents a slight prominence in its centre, and is separated by a slightly perceptible contraction from the hemispheres which it unites.
The central part or the pyramid ( pyramis , Malacarne) is next to this prominence, and is separated from it by a very deep fissure.
This central part projects in every direction much more than the posterior, and is attached, by much narrower and lower lateral parts, to the posterior half of the inferior external lobe, and to the inferior internal lobe.
Next to the pyramid, from which it is separated by a deep groove, comes a narrow part which is easily divided into several lobes situated one over another, and which generally is not perfectly symmetrical, being turned first to the right, and then to the left. This part also projects still more, in proportion to its breadth, and is continuous with the amygdalae by a narrow and deeply situated medullary band.
Finally, we next observe the anterior and smallest part, called the nodule ( nodulus , Malacarne), which is continuous on each side, with the posterior valve.
Thus, the central portion of the cerebellum, considered as a whole, is so curved, first from before backward, then from below upward, next fiom above downward and from behind forward, that the two extremities of the vermiform process, which proceed toward each other, almost touch, and are separated only by the narrow face of the summit of the fourth ventricle.
II. TEXTURE.
§ 1745. The gray substance surrounds all parts of the cerebellum, except its lower face which corresponds to the fourth ventricle ; this is covered with medullary substance. The latter is continuous in the three prolongations of the cerebellum, anteriorly with the tubercula quadrigemina, posteriorly with the medulla oblongata, below, and on the sides, with the annular protuberance, and extends within this organ in ramifications, the collection of which is termed the arbor vita ; of this we may be convinced by vertical incisions.
The medullary trunks follow a more or less curved direction, to near the circumference of the cerebellum, and give off, in this course, a greater or less number of branches, which arise from their convex edge.
A thin layer of yellow substance, covered by a thick layer of gray substance, exists on the surface of each medullary branch. This arrangement causes the lamellar structure of the cerebellum, since each layer incloses a layer of medullary substance, and each of the laminæ into which the principal layers divide always corresponds to a medullary branch.
The middle and lower part of the cerebellum presents this arrangement most distinctly. We find, in this place, seven medullary layers,
three anterior, three superior, and one posterior ; the upper of which are the longest, and ramify most simply.
All these layers become much larger from within outward, so that, with their covering of gray substance, they represent cones, the summits of which are turned inward, and the bases unite with the parietes of the fourth ventricle, and are separated from each other forward by deep grooves.
The medullary substance is proportionally much less in the central part, upon which circumstance alone depends its smallness ; but externally it accumulates in a direct ratio with the enlargement of the hemispheres of the cerebellum.
§ 1746. A vertical section demonstrates that the medullary nucleus is thickest below, in the centre of the cerebellum, before the summit of the fourth ventricle, opposite the second and third segments, consequently in its anterior half. From this point to the circumference it grows thinner as it ramifies ; but we constantly observe that the medullary layers of several lobes are much broader, toward the surface of the organ, than they are when thejr aiise from the central nucleus.
This arrangement is not observed in the fourth lobe, the uvula, the pyramid, the cerebral valve, and the anterior vermiform process ; but it is very perceptible in the other two segments. In the anterior lobes of the third segment the medullary layer, soon after leaving the nucleus, swells out considerably in passing through the lobes. The layer of the upper and the posterior lobes arises from a nucleus, almost as large as the central medullary nucleus, situated before the summit of the fourth ventricle. In the fourth segment we find a similar, but smaller, nucleus, more than six lines long, which is attached to the central nucleus by a thin filament.
§ 1747. In following this method, which is undoubtedly the' strictest, we arrive at a new division of the medullary layers of the centre, and of the hemispheres of the cerebellum, very similar to the division mentioned above, but different from it in some *espects.
The first of these seven layers belongs to the posterior part of the anterior valve. It is the smallest, and the folds of the posterior part of the valve rest upon it.
The second is formed by the anterior vermiform process, and the anterior part of the upper anterior lobe.
The third is much larger, and belongs to the anterior part of the monticule, and to the larger middle part of the upper anterior lobe.
The fourth, the most posterior, corresponds to the most posterior part of the monticule, to the commissure of the upper posterior lobes, to that of the lower posterior lobes, to the most posterior part of the upper anterior lobe, to the upper posterior lobe, and to the upper part of the lower posterior lobe.
The fifth is composed of the pyramid, of the lower smaller part of the lower posterior lobe, and of the digastric lobe.
The sixth corresponds to the uvula and to the amygdalæ. Finally,
The seventh, forms the nodules and fourth lobe ; it is the smallest of all, except the first.
The last two are distinguished from the rest, as they are not cleft and covered with a gray substance, except in one part of their circumference, forward and backward. The first presents this arrangement in every part, and the latter at its upper posterior part. The others are divided several times on each side ; they however present traces|of the arrangement above mentioned, because the lower anterior half of the segments, which are turned the most forward, and the lower posterior half, which are turned backward, present the most simple and shortest grooves and ramifications, the former downwardand backward, the latter downward and forward.
CORPUS FIMERIATUM,
§ 1748. In the centre of the medullary substance in each hemisphere of the cerebellum, little more internally than externally, we find a rounded, oblong, very vascular body, medullary internally, surrounded with a serrated edge, and intimately united to the medullary substance, called the rhomboid or fimbriated body ( corpus rhomboideum , s.fimbriatum , s. dentatum). Its gray edge mostly surrounds it, except its lower anterior part, where the medullary substance within it is continuous with that of the walls of the fourth ventricle, so that the hemispheres of the cerebellum are consequently composed of a double layer of medullary substance, and of gray substance ; the internal, formed by the corpus fimbriatum, and the external, comprising most of the external medullary substance and the external gray substance.
We here then find the repetition of what is observed in the medulla oblongata, in the olivary bodies, and the pyramids; (§ 1726-1727) only this form exists here in a greater degree, since the rhomboid body of the cerebellum is not only surrounded with a thin and smooth layer of white substance, as is seen in the medulla oblongata, but this layer is much thicker there, and not only forms several successive ramifications, but is covered a second time with grey substance.
§ 1749. The medullary substance of the cerebellum is extended in three fasciculi, which, however, are not distinctly separated ; they are called the prolongations of the cerebellum ( crura cerebelli). One is inferior and descending, another middle and anterior, the last is superior and ascending.
The inferior descending prolongation ( crus cerebelli descendons , s. ad medullam oblongatam) blends with the posterior cord of the spinal marrow or the restiform body. The superior ascending ( crus cerebelli adscendens, s. ad eminentiam quadragesimam ) goes to the posterior tubercula quadrigemina. The middle lateral or anterior ( crus cerebelli ad porlum) goes forward and downward, and blends with the annular protuberance. Of these three prolongations, the third is the largest. The first two are situated farther inward, and surrounded by it, so that the rhomboid body exists between it and them. They blend forward and backward, and seem developed principally to form the middle region of the cerebellum, while the hemispheres of this organ rest on the lateral prolongations, so that the medullary layers which form them, are directed* forward in the upper lobes, and backward in the inferior.
When we separate longitudinally a cerebellum hardened by immersion in alcohol, it is divided into an upper and lower half ; we also see on one side a very broad but thin transverse medullary layer, which contracts and at the same time becomes thicker from before, backward and outward, and which is expanded to form the lateral prolongations : we have on the other side, particularly towards the centre, fasciculi which intercross from before backward, so that the ascending and descending prolongations, at least to some extent, are not directly blended with each other, but reciprocally interlace.
§ 1750. The cerebellum forms most of a ring, which is constituted below by the lower part of the annular protuberance, embraces the cerebral peduncles, and unites by its anterior and posterior prolongations, with the medulla oblongata, and with the cerebrum.
III. WEIGHT.
§ 1751. The cerebellum, if separated at the place where its prolongations enter the annular protuberance, the cerebrum and the medulla oblongata, generally weighs five ounces. Its weight consequently, is to that of the rest of the encephalon, as 1:8, or as 1 : 7, rarely as 1 : 10, or even as 1 : 11.(1) In the latter case, we must attribute its excess of weight to the suspended development of the encephalon.
IV. CONSISTENCE.
§ 1752. The cerebellum has about the same consistence of the cerebrum, and like this, it is softer than the medulla oblongata, and harder than the spinal marrow.
ARTICLE THIRD.
CEREBRUM.
I. EXTERNAL FORM.
§ 1753. The cerebrum forms most of the cephalic portion of the centre of the nervous system, and occupies its upper and anterior region.
Considered as a whole, its form is a rounded oblong, and it is for the most part convex. Its length exceeds its breadth, and particularly its height. Its greatest length is six inches, its greatest breadth is five, and its height is four. It is broadest and highest in its centre.
It is formed of two lateral and perfectly similar halves, called hemispheres or lobes (hemisphere,, lobi, Chaussier). These two halves are separated at their upper part by a longitudinal fissure ( fissura Icngitudinalis), much broader backward than forward ; in the former direction its breadth is half an inch, but hardly a line in tire latter. They are on the contrary, almost blended with each other at their middle and lower portion.
(1) Chaussier, loc. cit., p. 77.
Each hemisphere is divided into two lobes (lobi, lobuli, Chaussier), an anterior and a posterior. The anterior is more than twice as large as the posterior. They are separated by a groove more than an inch deep, the direction of which is oblique from above downward, and from behind forward ; this is called the groove of Sylvius ( fossa Sylvii), Red terms it the valley. This separation exists only below and on the side, for the groove does not extend to the upper face.
The posterior lobe is also frequently divided into two others, termed the middle and posterior lobe. The latter forms that part of the cerebrum which rests on the tentorium. It cannot be distinguished externally from the middle lobe, but is separated from it on its internal face by a fissure, the direction of which is obliquely from above downward, and from behind forward, and on the lower face by a slight depression.
In each hemisphere we distinguish an inferior, an external, a superior and an internal face.
I. INFERIOR FACE.
§ 1754. The inferior face should be examined first, for we there recognize most distinctly, that the cerebrum is directly continuous with the medulla oblongata.
Of the three faces, this is the most irregular, and its central portion is entirely separated from the two lateral parts.
I. MIDDLE REGION.
I. CEREBRAL PEDUNCLES.
§ 1755. We first observe from behind forward, directly before the anterior edge of the annular protuberance, (§ 1733) the cerebral peduncles, or the crura of Ike medulla oblongata (crura cerebri magna, crura ad medullam oblongatam). They are two large rounded bodies, about eight lines long, which become much larger from before backward, seven lines broad posteriorly, ten anteriorly, ten lines high, grooved longitudinally, and entirely formed of substance, white externally. They diverge from each other behind forward, and are separated at their lower part by a very broad and deep groove; this is only the anterior groove of the spinal marrow, which is deepened by the development of the peduncles. This part forms above the floor of the aqueduct of Sylvius ; its lower face is gray, and numerous vessels pass through it, the direction of which is from below upward, and from without inward. Vicq-d’Azyr(l) terms it the middle perforated substance (substantia perforata media).
(1) Lac. cit., p. 545.
Near the posterior extremity of these bodies there is generally a transverse and slightly projecting band which passes over all their lower face, and crosses the longitudinal groove. A second posterior transverse band is detached from where the anterior and middle prolongations of the cerebellum unite, and is directed from behind forward, and from above downward between the two peduncles, proceeding on their lower face. This band is situated directly before the annular protuberance, and is often united with it, representing to a certain extent a distinct edge. The cerebral peduncles are covered posteriorly by the anterior part of the annular protuberance, forward by the root of the optic nerve, which turns on them from above downward, from without inward, -and from behind forward.
§ 175G. The cerebral peduncles are formed externally by a layer of white substance about two lines thick. Next comes a rounded and elongated layer of blackish substance, which has a semicircular form, as has the whole cerebral peduncle, being concave above and convex below. Next comes a third layer, the thickest ; this extends upward to the surface, and is formed of a mixture of gray and of white substance.
§ 1757. Between the anterior extremities of the two cerebral peduncles, is a broad triangular surface, which enlarges very much from behind forward, and is continuous posteriorly with the middle portion, anteriorly with the anterior part of the perforated substance of the lower face. The direction of this surface is from behind forward, and from above downward at its posterior part, from below upward, and from behind forward at its anterior part, which is more perpendicular than the other ; it forms the floor of the third ventricle. We remark from behind forward the mammillary eminences, the infundibulum with the pituitary gland, the anterior part of the root, and the decussation of the optic nerve ; the rest of it is formed of gray substance.
II. MAMMILLARY EMINENCES.
§ 1758. The mammillary eminences or pisiform tubercles , ( eminentiœ medulläres , s. candicantes , s. mammillares , Chaussier) are situated side by side between the anterior extremities of the cerebral peduncles ; they are two hemispherical prominences, formed externally of medullary substance, and internally of cortical substance, about half a line distant from each other in their whole height, but separated a littlefarther posteriorly. They are the inferior and anterior extremities of the fornix.
When attentively examined, we observe that these triangular eminences are each composed of a larger inner, and a much smaller outer half. The anterior and inner faces are straight, the posterior is convex ; the latter is the longest, the inner is much the shortest. The two halves of each eminence are very distinctly separated ; the internal projects very much ; the outer terminates in a point on the outside of the gray substance, between the mammillary eminence and the optic nerve.
III. INFUNDIBULUM AND rlTUlTARY GLAND.
§ 1759. We find a rounded and conical prolongation between the mammillary eminences, called the infundibulum ;( 1) this descends obliquely forward, and terminates in the pituitary gland or body ( hypophysis cerebri , s. glandida pituitaria, Chaussier).(2) This is situated in the sella-turcica of the sphenoid hone below the dura-mater, which covers its upper face, and is closely surrounded on all sides. The lower extremity of the infundibulum, is connected with it by a narrow opening in the dura-mater. The lower and the upper parts of the infundibulum are thicker than its centre. In its first two parts it is about a line thick. It is formed of gray substance.
The pituitary gland has an oblong rounded form. It is about six lines broad, three long, and less than three high ; it generally weighs, including the infundibulum, eight grains. It is always formed of an anterior and a posterior lobe, which are intimately united. The anterior is very large, and generally twice the size of the other.
The anterior is bean-shaped ; the posterior is more rounded, and is situated in the posterior and serrated edge of the anterior lobe.
The pituitary body is generally very hard, but its posterior lobe is softer than the anterior.
The anterior lobe is formed of two substances, an external reddish, and an internal which is white, which vary much in their degree of color and their proportional quantity. We rarely find one which is homogeneous. We observe on the right and left side, on the limit between the two substances, a depression in which those small ducts which arise from the external substance terminate. The posterior part of this depression forms a small canal, which, converging with that of the opposite side, goes towards the centre of the posterior edge of the lobes, and the place where the infundibulum is continuous with the pituitary body ; the two canals unite in this place.
The posterior lobe has uniformly a more or less grayish tint.
Both lobes are directly attached to the infundibulum, which always descends on the upper face of the pituitary gland to the place where they unite, and are surrounded with it by a prolongation of the piamater.
The infundibulum is formed of gray substance, a continuation of that of the floor of the third ventricle, and it is considerably narrower in its centre than above and below, where it is several lines thick.
jl) A. Murray, Observationes anatomicœ circa infundibulum cerebri , ossium capitis in feetu structuram alienam partemque nervi intercostalis cervicalem, Upsal, 1772.
(2) Wenzel, Observations sur le cervelet et sur les diverses parties du cerveau dans les epileptiques , 1811. — Rayer, Observations sur les maladies de l'appendice sussphenoidal du cerveau ; in the Archiv, gen. de medecine, t. iii. p. 320. — See also the extract from Guersent’s case, same journal, v. iii. p. 312. — Ward, Case of amaurosis produced by enlargement of the pit uitary gland ; in the Land. med. repository, 1823, t. xx. p. 217.
Opinions vary in regard to the nature of the infundibulum ; some think it entirely hollow ; others on the contrary that it is solid ; and some assert that it is sometimes solid and sometimes hollow.
Although a canal is not always visible within it, as some writers have asserted, particularly the old anatomists, and Murray among the moderns ; it -is sometimes hollow in all its extent, and we can always introduce into it air or liquids, pushing them from the pituitary gland into the third ventricle ; but this is more difficult, and even fails when attempted in the opposite direction from the ventricle towards the pituitary gland. The infundibulum may serve to transmit into the cerebral ventricles, a fluid which is secreted by the pituitary gland.
Sometimes, but rarely, we find within or on the surface of the pituitary gland, a solid and sandy substance ( acervulus cerebri.){ 1)
IV. BOOT AND DECUSSATION OF THE OPTIC NERVE.
§ 1760. The larger anterior and inferior partof the rootof theoptic nerve which is the largest, and the decussation of this pair of nerves, follow the two bodies described in the preceding paragraph ; these parts are situated outwardly on the anterior extremity of the cerebral peduncles, inwards and in the centre before the grayish plate which forms the inferior wall of the third ventricle, from which the optic nerve receives in the angle formed by the union of its anterior with its posterior half, filaments which may be regarded as its anterior root.
When speaking of the optic nerve, we shall give a more detailed description of the course and union of its roots.
V. GRAY PLATE OF THE INFERIOR WALL OF THE THIRD VENTRICLE.
§ 1761. The gray plate (tuber cinereum) of the inferior wall of the third ventricle, is thicker in its posterior than in its anterior half, which is extremely thin, so that it tears very easily, merely from its weight, when the brain is turned over and all its sides are not well supported. It is continuous forward with the anterior extremity of the corpus callosum, where it forms on the surface of the anterior commissure a thin expansion, across which we perceive this cord.
II. LATERAL REGIONS.
§ 1762. The two lateral regions of the lower face of the cerebrum, are much more extensive than the central. Their internal edges touch anteriorly and posteriorly where they are separated only by the falx cerebri, while in the centre, there is a space filled by the parts we are about to describe.
(1) Bichat, Anat. descript., voL iii. p. 75.
This larger part of the lower face of the cerebrum, is formed by the lower face of the posterior and of the middle lobe. It presents a slight concavity posteriorly in all that part which corresponds to the posterior lobe, which is entirely covered by the cerebellum. Anteriorly it is slightly convex, loose, and terminated by a rounded extremity. Its anterior part projects considerably, and forms the lowest region of the cerebrum. It extends to the small wings of the sphenoid bone, and passes about an inch beyond the central part, which terminates by the decussation of the optic nerves.
This blunt anterior extremity of the middle lobe is loose, and covers the inferior extremity of the lateral part of the fissure of Sylvius. Behind it, the lower face of the middle lobe forms at first a large convex eminence, which rests outwardly on the base of the skull, and which covers within, the posterior part of the root of the optic nerve, with which it is united only by a short cellular tissue, and by the pia-mater.
This eminence is the commencement of a conical projection, which contracts from before backward, and marks in this place the transition from the external to the internal face of the cerebrum, and forms the posterior part of the inner edge of the middle lobe. The upper part of the eminence, the hook, has a direction from within outward, and from before backward, and terminates in a blunt extremity, which is continuous with the medullary semicircular band. The loose and concave edge of which is turned forward, while its attached and convex edge looks backward. This band called the corpus fimbriatum ( tœnia , s. fimbria), enlarges inward and upward. When th'è cerebellum is turned downward and forward, we see very clearly that it blends with that of the opposite side, and forms the posterior part of the fornix. Below, it is a longitudinal band, which has the same direction, but is less prominent ; this is termed the fascia dentata. The latter extends forward a little farther than the preceding, and is covered by the external part of the base of the hook. It gradual^ enlarges from before backward, and presents numerous elevations and depressions situated longitudinally one after another.
The lower part of the internal edge of the lower face of the eminence which has the same direction, but which projects more, extends backward, upward, and inward, and is continuous with the posterior part of the corpus callosum. Its most internal part, which presents a convexity upward and downward, is white and smooth. The gray substance is seen where this internal part is continuous with the lower face of the cerebrum, and there also its circumvolutions commence, at least, unless we consider the fascia dentata as a rudiment, which seems more correct, inasmuch as a layer of gray substance, which communicates with the rest of the cortical substance of the brain, passes from each side to the posterior extremity of the corpus callosum on the origin of this inferior medullary layer, and is continuous with the fascia dentata. The circumvolutions arise imperceptibly in this place from the white band which we last described ; and the most internal forms a considerable longitudinal prominence, which is not interrupted by transverse striæ, or at least by none which are very manifest.
The lower face of the anterior lobe, which is slightly concave and the internal edge of which descends much lower than the external, are situated before the anterior extremity of the middle lobe. The internal edges of the two lobes approach each other very much.
The middle lobe and the anterior lobe are separated by the internal part of the entrance of the fissure of Sylvius. This entrance corresponds entirely to the lower face. Its most internal part is loose, and is continuous with the thin plate situated before the decussation of the optic nerves; (§ 1761) it becomes broader from within outward, and is perforated with numerous considerable openings, which increase in diameter from within outward, and give passage to the vessels sent off by the origin of the middle cerebral artery into the cerebral substance. This is termed by Vicq-d’Azyr the anterior perforated substance (substantia perforata antica).{\ ) and by Reil, the cribriform plate ( lamina cribrosa).( 2)
This cribriform plate is formed almost entirely of gray substance. It is, however, white internally in its centre, whence arise the lateral longitudinal striæ of the corpus callosum, which go upward and inward. It is continuous outward and backward at the inner part of the summit of the middle lobe, and farther forward, with a small smooth elevation, about half an inch broad, where the white substance is exposed, and where the anterior and posterior lobes unite, without being separated by a deep fissure.
The olfactory nerve proceeds at a little distance in a deep groove, along the inner edge of the lower face of the anterior lobe ; its direction is from before backward, from above downward, and from without inward, and it is united to the lobe by the pia-mater, which extends like a bridge on its upper face.
The extremity of this longitudinal groove, which is much deeper than the optic nerve is high, is bounded by a triangular tubercle, the olfactory tubercle ( processus , s. carunculus mammillaris ), from whence the nerve partly arises. We also see a white band proceeding from it ; this goes backward, upward, and outward, and terminates in the fissure of Sylvius, at the union of the anterior and posterior lobes, at the point where the white substance becomes visible externally.
(1) Loc. cit., p. 545.
(2) Archiv. fur die Physiologie, vol. ix. p. 199.
II. EXTERNAL FACE.
§ 1763. The external face is convex, and is most prominent in its centre on each side upward and downward. It is imperceptibly continuous with the upper and lower faces, less however with the first than with the second. The fissure of Sylvius divides it into an anterior and a posterior half. At first view this fissure seems only an indentation, the direction of which is obliquely from below upward, and from before backward, and is situated at about the centre of the lateral face, a little nearer its anterior than its posterior extremity, the parietes of which are formed, the inferior by the upper face of the anterior part of the middle lobe ; the superior, on the contrary, by the lower face of the middle part of the anterior lobes, and we may consider its posterior extremity as the upper limit of the external face. An attentive examination, however, soon shows that it has much more extent. In fact, at the outer extremity of the anterior cribriform plate, (§ 1762) the commencement of the fissure of Sylvius, hitherto single, divides into an anterior and a posterior groove. The posterior is that just described. The anterior is much shorter, goes directly upward, and communicates with the posterior extremity of the posterior, by a third groove, which proceeds directly from before backward. These three grooves consequently include a triangular space, the lower part of which is seen where we separate the two parietes of the posterior groove ; but we cannot see its whole extent until we have opened the superior horizontal groove, by raising that part of the anterior lobe which forms it anteriorly. We then observe that the central part of the anterior lobe, at first convex, goes from below upward into this middle portion of the fissure of Sylvius, and thus forms a triangular space called the island of the fissure of Sylvius , then immediately descends again before its larger upper part, resting upon it, then describes a right angle to go directly outward for about an inch, and finally joins, also at a right angle, the external face of the hemisphere, and particularly of the anterior lobe. The lower and horizontal face of this reflected portion of the anterior lobe, which may be called the roof of the fissure of Sylvius , is situated at the upper face of the anterior and inferior part of the middle lobe, so that it entirely conceals the island.
The latter is about two inches long and an inch and a half high forward. It terminates backward in a blunt summit, and curves outward. We remark on its surface three or four flat circumvolutions, which diverge and enlarge from below upward ; the anterior of these are shorter, but broader, perpendicular, and parti } 7 also go directly a little forward, while the posterior are longer, narrower, and proceed more obliquely backward. Both arise from the right portion, where the two lobes join and emanate as from a common centre of irradiation.
These circumvolutions are separated from those of the middle lobe by a smooth space about four lines broad ; but they are so intimately united anteriorly with those of the anterior lobe, that they seem to be the continuation of it.
III. UPPER PACE.
§ 1764. The upper face is very convex from before backward, in which direction it curves uniformly. It is only slightly convex from without inward. It is the longest face of the brain.
IV. INTERNAL FACE.
§ 1765. The upper face forms a right angle with the internal, which is perpendicular and straight. This latter face is placed against that of the opposite side, from which it is separated by the falx cerebri. When the two internal faces are separated, we see at their base, the upper part of the corpus callosum, which unites them in most of their length.
Behind the posterior extremity of the corpus callosum, there is most generally, but not constantly,(l) a deep groove, almost perpendicular, which may more properly be regarded as the limit between the posterior and the middle lobe, inasmuch as it corresponds exactly to the commencement of the posterior horn of the large lateral ventricle, and lodges the posterior cerebral artery.
V. CIRCUMVOLUTIONS AND ANFR ACTUOSITIES.
§ 1766. The upper, the internal, the external, and most of the inferior face of the outer surface of the cerebrum, is uneven from numerous elevations and depressions there seen.
The elevations called circumvolutions ( gyri ), from the curves they describe, are situated between the depressions termed anfractuosities (sulci), so that each is included between two grooves. They are covered in every part, outwardly by a layer of gray substance, which is at most but a line or a line and half thick. They are formed of medullary substance, and hence the latter alone determines the form of the surface of the brain. The external layer of gray substance is single in almost every part ; and it is almost always divided, only in a slight extent in the posterior and inferior circumvolutions of the internal face of the hemispheres, by a band of white substance, into an external and an internal layer, (2) so that the structure of this part of the brain is more complex than the rest. The medullary band is infinitely thinner than the two gray layers, which together are not thicker than a single layer, and of which the internal is sometimes equal to that of the external, and sometimes also greater or less than it. However constant may be this arrangement in this place, we have never found it else where, except in the cornu Ammonis.
(1) Scemmerring', De basi encephali, tab. iii.
(2) Vicq. d’Azyr, in the Mëm. de Paris, 1781, p. 606.
The circumvolutions have a rounded surface, and are situated directly
at the side of one another, so that the prominences of one correspond to the depressions of another, although where the angles are very
re-entering, the prominent part of an adjacent circumvolution oe not
perfectly till them ; whence, in many places, particularly in those where
large curves are observed, triangular spaces exist, which are included
between two circumvolutions. But even in these places, the latter
approach or touch at the bottom of the anfractuosities.
These circumvolutions vary much in the manner in which they are continuous with one another.
Their height and breadth are not uniform in every part ; the latter generally, being some lines greater. They are usually a little more than an inch high, and a little less than an inch broad.
We generally observe in the places where they are broadest, a greater or less depression, which has most commonlly, but not always, the direction of the length of the circumvolution, and the depth of which is usually proportioned to the breadth of the latter. This groove evidently marks the division of the circumvolution into two. It is more rare to see analogous depressions extending transversely from one edge to the other.
These circumvolutions are not perfectly similar either in different subjects, or in the two hemispheres of the same cerebrum : they differ, on the contrary, very much, which circumstance may be considered as a character peculiar to the cerebrum of man, since as Yicq-d’Azyr has already remarked, (1) the' cerebrum of the other mammalia is much more symmetrical. Those on the lower face are much more symmetrical, and more constant than the lateral and the superior. The former are mostly longitudinal, the others have every direction. The anterior and the posterior are generally smaller than the middle.
§ 1767. After describing the parts of the surface of the cerebrum of the brain, which are observed without any derangement of this viscus, and which may consequently be called the external , we proceed to describe in the same order, those which are seen after partially or wholly raising the preceding, according to the situation which they occupy, without having any regard at present to their connections with each other, or with the whole cerebral mass.
I. TUBERCULA QUADRIGEMINA.
§ 176S. The tubercula quadrigemina (eminent ia quadrigemina , s. bigemina, s. nates et testes), form a square mass, situated forward and laterally between the posterior extremities of the optic beds, below the pineal gland and the posterior commissure, before the cerebellum, and above the cerebralpeduncles. This mass is oblique from above downward, and from before backward; it is about nine lines long, and ten or twelve
(1) Mem. da Paris , 1783, p. 512. — This subject has been more fully treated by Wenzel, loc. cit., p. 23.
broad, and weighs half a drachm. It is composed of two pairs of rounded eminences, situated one after another from before backward. The anterior eminences are usually the largest, and about one line broad. They are called the nates , the posterior and the testes cerebri. The relation of the weight of the whole mass is to that of the whole cerebrum as 1 : 576. The four eminences are separated by a crucial depression. The anterior are usually more gray than the posterior ; this difference of color is rarely as evident in the cerebrum of man, as in that of several animals, particularly the ruminantia.
The eminences are of a grayish red internally, and are surrounded with a very thin medullary layer, so that the reddish tint they present, depends upon the color of the gray substance appearing through the external envelop. The layer on which they are placed, is of a much deeper gray, and is continuous with the gray substance of the cerebral peduncles.
A considerable medullary band proceeds from the anterior extremity of the anterior eminences ; this goes forward towards the tubercle, which terminates posteriorly the inner face of the optic bed : a second band also extends either directly to the optic nerve, or to the internal corpus geniculatum, or even in part to the external. Another, which is still larger and longer, is detached from the posterior eminences : this goes to the rounded prominence of the lower extremity of the posterior face, that is, to the external corpus geniculatum.
The tubercula quadrigemina, cover the upper part of the cerebral peduncles. They form an arch extended over a small space called the aqueduct of Sylvius ( aquæductus Sylvii), which establishes a communication between the fourth and the third ventricle.
In the bottom and on the sides of this aqueduct, we remark longitudinal depressions, to which we shall return when describing the cerebral ventricles.
A narrow, prominent, medullary band, descends between the two posterior eminences from about their centre : this is situated exactly on the median line, and terminates in the large cerebral valve.
II. PINEAL GLAND.
§ 1769. The pineal gland, conarium , Ch. ( Gl. pinealis, conarium ), is an oblong rounded body, much broader from right to left than from before backward, solid, blunt at the extremity, of a very deep gray, sometimes of a reddish color, from three to four lines long, two to three broad, two thick, and weighing three grains, which always exists in the cerebrum, and which, probably, has not been found, owing to a superficial examination for it. This body is turned from before backward, and is attached anteriorly by its base by two thin medullary cords, which diverge from behind forward to the thalami optici, between which it is situated at their posterior part, but some lines distant from them on each side. Tt entirely covers the centre of the upper face of the anterior tubercula quadrigemina. Posteriorly, a medullary layer is detached from its base, which first goes forward, also blends with the upper face of the thalami optici, then immediately curves backward and goes to the point where the anterior pair of the tubercula quadrigemina unite. This is termed the 'posterior small cerebral commissure, which is thinner at its anterior than at its posterior part, the first of which sometimes sends to the pineal gland, filaments similar to nerves, while the second always presents transverse grooves, which soon disappear on each side. The pineal gland always incloses at its posterior part, a small cavity, which varies in size ; its orifice is turned toward the middle cerebral ventricle, and the internal face of which is sometimes very manifestly lined by a medullary layer. This cavity is rarely closed in all parts, and its parietes are also proportionally very thick. The variations in its capacity depend neither on the age nor on any other constant condition. It is more consistent than the gray substance generally.
Before this gland, at its circumference, in its cavity, or finally in its substance, and sometimes in all these points at the same time, we find a yellowish substance, which is rarely abundant, but semitransparent, brilliant, hard, and formed of grains apparently irregular, but which are in fact rounded, and the diameter of which does not exceed half a line.
( acervulus cerebri, s. glandules pineales) .{ 1)
With some rare exceptions, (2) this hard substance is constantly found after the seventh year according to Wenzel, (3) and sometimes at least after the sixth, according to our observations. Before this period we find in its place a more viscous mass, which is not more unfrequently found at an advanced age, and which then sometimes even coexists with the concietions.
In young men the concretions of the pineal gland are usually found only around the organ and in its cavity, while in old men it also exists in its substance, or even only in the latter.
Their color is not always perfectly the same ; generali}' they have a brighter tint in youth and in advanced age, than during the other periods of life. We however observe in this respect, differences which do not depend on the age. The larger calculi are usually darker than those which are small.
In regard to the proportional quantity of these concretions, it is least in youth and in advanced age. In this respect, however, we observe differences which cannot be referred to a determinate cause. The number of the concretions, also, has no direct ratio with the size of the pineal gland.
(1) Sommerring, De acervulo cerebri, Mayence, 1785, ed. ii., in Ludwig, Opp. neuro’.., vol. ii. p. 322.
(2) We have never known it to be deficient. Wenzel has observed its absence only six times in one hundred cases, (p. 156).
(3) Loc. cit., p. 135.
These concretions and the mass which they form, are united with each other, and with the adjacent parts, by a dense cellular tissue, and by an envelop like a sack. The mass is composed not only of a certain number of smaller masses, but each of these latter are formed of several calculi, which are all perfectly round.
Exposed to the air, these concretions become dry, opaque, and whitish. They seem entirely, or almost entirely, similar to the bones in their chemical composition^ 1)
The calculi of the pineal gland, are not a pathological appearance and the cause or the effect of the diseases of the mind,(2) as Morgagni, (3) Gum, (4) and Greding(5) assert, because they are found in very small quantity in four individuals who were fools. (6) Although they are not unfrequently less abundant than usual, when there is no derangement in the mind ; still the coincidence of their rarity with mental derangement, is curious, inasmuch as the fewness of these concretions in young and in old men, seems to lead to something analogous.
III. CORPUS CALLOSUM.
§ 1770. The corpus callosum , mesolobe , Ch. ( corpus callosum ., trabs cerebri , commissura cerebri magna), (7) is situated between the two hemispheres and unites them.
It is nearer their anterior than their posterior extremity, and occupies about the second and third anterior fifths of the length of the cerebrum, considering the length to be divided from before backward into five equal parts. It is, however, a little longer than two fifths.
It is about three inches long and eight lines broad. It gradually enlarges from before backward, but again contracts a little nearer its posterior extremity. In most of its length, excepting the middle, it is covered by the lower part of the internal wall of the hemispheres, v hich advances on it, whence a deep depression in form of cul-de-sac, is formed on each side, somewhat analogous to the lateral cavities of the larynx. Its mean thickness is about three lines.
It is uninterruptedly continuous on both sides, with the substance of the hemispheres, and there is no need of recurring to any artificial means to discover that it is formed of transverse medullary fibres, blended with grayish substance.
(1) Gordon, loc. cit.. p. 135. — Pfaff, who has analyzed these concretions, found
them composed of animal matter, and of much phosphate of limé, and a little of
the carbonate. See Deutsches Archiv, fur die Physiologie, vol. iii. p. 170.
(2) J. F. Meckel, Mém. de Berlin, 1754, p.Ç92. — Rcederer, De cerebro, Gottingen, 1758.- — Morgagni, Decaus. et sed ., ep. lxi. a. 3, 4. — Sommerring, loc. cit.
(3) De caus. et sed., ep. v. 12.
(4) De lapillis glandulæpinealis in quinque mente alien., Leipsic, 1753.
(5) Advers. med., vol. ii. p. 522.
(6) Wenzel, loc. cit., p. 165.
(7) Reil, Sur le système et V organisation du corps calleux ; in the Archiv, für die Physiologie, vol. x. p. 171-175.
The anterior extremity of its upper face is convex, and the posterior
is concave, an arrangement which undoubtedly depends on the separation of the two hemispheres from each other from before backward.
The posterior edge is broader than the anterior.
On its upper face there is a superficial depression which extends through all its length, and corresponds exactly to the median line. Along this depression there is on each side a slight elevation, called the raphe , or the external suture of the corpus callosum (raphe, s. sutura externa corporis callosi). The raphe is not formed solely by the artery of the corpus callosum, but it is a sort of cicatrix, produced by the mutual adhesion of the two hemispheres.
Independent of this depression, we also remark on the upper face of the corpus callosum, two longitudinal striæ, generally broader, which proceed on each side parallel to each other, although not perfectly symmetrical ; these are called the lateral longitudinal striæ ( striæ longitudinale laterales). Reil terms them the covered bands, because they are situated below the part of the hemispheres which projects inward, and which almost entirely covers the lateral part of the corpus callosum.
Transverse fibres exist also on each side, on this upper face : they leave the median line, and are continuous with those of the hemispheres.
We also observe transverse elevations on the lower face ; but the latter resemble still more the fasciculi, separated from each other by superficial depressions. They arise from the inferior face of the corpus callosum, being concave and less extensive than the superior. In fact, the transverse fibres extend through all the thickness of the corpus callosum.
These fibres are not transverse at the anterior and posterior extremities of the corpus callosum : they there have a direction from before backward, and from without inward in the first, from behind forward and from without inward in the second, so that they converge.
The corpus callosum is curved at each of its extremities. It is inflected from before backward, and from above downward at its anterior extremity, from behind forward, and also from above downward at its posterior extremity. Reil termed the anterior curve the knee, and its extremity the beak, the posterior the glove. These two curves connect the upper and lower faces of the corpus callosum.
The latter is much more complex than the other. After leaving the knee, it descends from before backward, extends to the anterior commissure, reascends from behind forward, is parallel to the upper face, again proceeds forward, then a third time backward, and is finally continuous with the upper face, after giving origin to the glove.
This lower face is loose only at its anterior and its posterior part, forward from the knee to the anterior commissure, backward to its union with the arch ; every where else it is uninterruptedly continuous with the septum lucidum.
The commencement of the lower face from the knee to the anterior commissure, gradually becomes more and more narrow. From the knee to its centre, the upper raphe and the longitudinal lateral striae are vety distinct. But the raphes disappear in this place, the striae approach each other still nearer from before backward, but do not touch ; and at the same time the lower face is grooved from the extremity of the superior raphe to the commissure, where it terminates by a small depression in form of cul-de-sac ; consequently the two lateral halves of the corpus callosum are, in this place, less broad, and less flat, and have the form of a straight layer ; but then' internal faces are inclined one towards another, whence comes the longitudinal groove which we have mentioned.
Hence, also, the part of the corpus callosum, covered by the hemispheres, becomes narrower from before backward, after leaving the knee, so that the most posterior part is entirely disengaged, and it is directly continuous with the ascending internal face of the anterior lobes of the cerebrum. Hence, also, the lateral longitudinal striæ are entirely loose in this place. They are directed backward, downward, and outward, and proceed below and before the anterior commissure, between it and the decussation of the optic nerves. At the posterior extremity of the lower face of the posterior lobe, they unite to the cribriform plate or anterior perforated substance of the lower face of the cerebrum, so that in this place the corpus callosum is continuous, through them, with the lower face of the anterior and the middle lobes ; although we cannot term the lateral longitudinal striæ the peduncles of the corpus callosum, as has been done by Yicq-d’Azyr.
Posteriorly the corpus callosum is also reflected on itself from above downward, and from behind forward. As the superior face of this reflected portion is adapted to the lower face of the straight portion, it forms what Reil has termed the glove.
The septum lucidum is attached to all the rest of the lower, face of the corpus callosum, which may be called its internal portion, in opposition to the upper and loose par' of the inferior, considering the latter as external.
The corpus callosum is continuous at its posterior extremity in the posterior and descending horn of the lateral ventricles, partly with the roof of these cavities, partly with the medullary covering of the eminences they enclose, the pes hippocampi minor and the cornu ammonis, which will be described hereafter.
IV. SEPTUM LUCIDUM.
§ 1771. The middle and anterior region of the part of the cerebrum which extends from before backward on the median line, forms the septum lucidum, (l) septum median, Ch. (Septum pellucidum, s. lucidum). (2) This septum, which is extended vertically between the corpus
(1) A very improper term, for the septum is but slightly, or even not at all transparent.
(2) Meckel, Obs~ sur la glande pineale, sur la cloison transparente, etc., in the Mém. de Berlin, 1765, p. 91-102.
callosum and the fornix is triangular. Its height and thickness are much greater anteriorly than posteriorly. It is continuous upward and forward with the anterior, horizontal, and reflected portion of the corpus callosum; posteriorly, but only to a slight extent, with the anterior portion of the fornix, and forms the larger anterior part of the common internal wall of the lateral ventricles.
It is composed of two layers, directly adapted one to the other, but they are not fused together. Each of these layers is formed in turn of an external thin and medullary stratum, and an internal thicker and gray stratum, the former of which is continuous with the medullary substance of the corpus callosum, and of the fornix. The medullary layer is lined by a very delicate membrane, which is demonstrated with peculiar facility, when there is an accumulation of serum in the space between the two layers.(l)
The space between the two layers is the ventricle of the septum, called also the fossa of Sylvius, the sinus of the median septum, Ch.
( ventricidus septi ), which is usually termed the fifth ventricle , and which Wenzel has called the first ventricle. This space does not every where present the same form or the same volume; but generally it is more spacious, and particularly broader in proportion, in the early periods of life, than afterward. Its breadth anteriorly is three or four twelfths of a line in the full grown fetus. It is usually about an inch and half long in the adult. It is always narrower in its centre, while at the anterior and the posterior extremity, it terminates in a triangular fossa, the angles of which are turned one towards the other.
Opinions are divided on the question, whether this ventricle is entirely separated from the others, or if it communicates with them, whether the communication be constant or simply accidental. Opinions differ also in regard to the position of this opening.
The ventricle of the septum is generally considered as a perfectly closed cavity. Our dissections have demonstrated that in the normal state it is always closed in subjects who are perfectly developed : it however much exceeds the limits generally assigned to it anteriorly ; for a canal which is at first rather broad, but which gradually contracts, and finally becomes very narrow, extends from its anterior part downward and backward, towards the third ventricle, to near the space between the anterior pillars of the fornix and the anterior commissure. We, however, cannot generally observe the orifice of this duct, although a communication between the third ventricle and that of the septum sometimes exists exactly in this place. (2)
(1) Sabatier, loc. cit., p. 433. — Meckel, Loc. cit., p. 96. — Wenzel, Prodr., p. 7. — Vingtrinier, Cas remarquable d’ hydrbpisie de la cavité du septum lucidum, ou cavité de Sylvius, chez une jeune fille idiote ; in the Revue medicale, vol. viii. p. 299
(2) Tarin, Anthropotomie, Paris, 1760, vol. i. p. 232. This septum sometimes opens by thè small fissure which separates the two cords of the anterior pillar into the lateral ventricles.
V. FORNIX.
§1772. The fornix, trigone cerebral, Ch. (fornix) loans t lie lower part of the upper and anterior wall of the third ventricle. It is uninterruptedly continuous upward and backward with the corpus callosum, forward in most of its length with the septum. The upper and attached edge is convex ; the lower is concave, and rests on the internal part of the upper face of the thalami optici, which it almost entirely covers, and is directed from behind forward, and from above downward. Posteriorly, the fornix is continuous by its posterior extremity with the corpus callosum. Externally, but first becoming broader, it joins uninterruptedly, the manifestly fibrous envelop of the cornu ammonis, then unites directly forward with the corpus fimbriatum. The posterior part of the fornix presents oblique and transverse striae in its centre, and has been termed, very improperly, the lyre ( lyra , s. ■ psalterium ), since, as Sabatier has already remarked, the Greek word ^aXXis does not mean a tyre but an arch ; hence too the term xapagiuv also applied to this part. The origin of the corpus fimbriatum, and the white envelop of the pes hippocampi, are called also the posterior pillars of ike fornix. We may consider the centre of this latter as its body. Anteriorly, the fornix descends directly behind the anterior commissure, then turns backward, and penetrates before and below the optic thalamus of its side, in the floor of the fourth ventricle, where it seems to disappear.
The portion of the fornix between its posterior extremity, and some lines beyond the anterior commissure, is flattened from above downward, and is single. After leaving this point, the fornix becomes cylindrical, and gradually divides into two lateral cords, which diverge from above downward, and are called its anterior pillars (crura fornicis anterior a), so that the anterior commissure which passes before them, is very evident in the interval between them. Each of these cords then glides below the optic bed of its side, in the floor of the fourth ventricle, directly above the decussation of the optic nerves. There, surrounded entirety by gray substance, it goes first outward, then again inward, so that it describes an arch very convex outwardly, whence opposite the union of the optic nerves, striæ descend into the decussation, where they may be easily followed, and it finally terminates in the gray substance of the mammillary eminences. We may then consider these latter as making part of the fornix, and Santorini is perfectly right(l) in terming them the bulbs of the fornix ( bulbi fornicis). The fornix, however, does not terminate in this place ; for a considerable medullary cord detaches itself from the mammillary eminences ; this proceeds within the optic bed, directly behind its internal face, covered in all parts by gray substance, enlarges above and expands in a fan. The mammillary eminences also give off a third medullary cord, which proceeds, at least in great part, nearer the surface, on the inner face of the optic bed, goes farther forward and divides into an anterior and a posterior fasciculus: the posterior follows from before backward the upper edge of the inner face of the optic bed, and is continuous with the peduncle of the pineal gland : the anterior goes outward, and is continuous with the semi- circular band, between the corpus striatum and the optic bed. Finally, the mammillary eminences also send backward and outward a third medullary cord, which is covered by the roof of the optic nerve, and goes to the optic bed.
(1) Obs. anat., vol. iii. c. 2.
Thus the fornix represents a very complex chain, which unites the two hemispheres in several parts, and which also establishes a communication between the anterior and the posterior parts of each hemisphere.
VI. THALAMI OPTICI.
§ 1773. The lhalami optici , or the posterior cerebral ganglions, the optic beds (ganglia postica, Gall, corpora striata posteriora et superna, Vieussens ; thalmni, s. colliculi nervorum opiicorum ), are two grayish, elongated, rounded bodies, which converge from behind forward, and from without inward, and are situated before the tubercula quadrigemina, envelop the anterior endsof thecerebral peduncles in most of their extent, especially upward and inward, so as to leave loose only a small part of them outward and downward, if we except the root of the optic nerve : but if we include this root, the cerebral peduncle is surrounded in this place by a complete ring, of which the optic bed is the commencement, and the union of the roots of the optic nerves the termination. These bodies are about an inch and a half long, nine or ten lines high, and from eight to ten broad. They weigh nearly four drachms, so that their weight is to that of the rest of the cerebrum, about as 1 : 36.
Their upper face is convex. We there remark a longitudinal projection, the direction of which is from before backward, and which is most prominent at its anterior part, and which imperceptibly disappears posteriorly. The most prominent part of this projection is the extremity of a large medullary fasciculus, which comes from the mammillary eminences, and expands superiorly like a fan.
The internal face is slightly convex, and almost straight at its anterior part, which is the most extensive.
It is continuous with the upper at an almost right angle. At the anterior part of its union with this latter, we observe a white medullary band about one line and a half broad. The bands of the two sides which are inflected to go to meet each other, unite on the median line, where they become the peduncles of the pineal gland, then go backward towards the mammillary eminences, slightly concealed forward and downward by the inner face of the optic bed.
Behind the posterior extremity of this medullary band, the internal wall is slightly convex, and terminates finally in a rounded prominence.
The optic beds are not united by the nervous substance at thenupper part, nor in those subjects which are perfectly developed, nor
even at the early periods oflife,(l) although Vieussens,(2) Santorini, (3')
Morgagni, (4) Winslow, (5) and Gunz,(6) have asserted the contrary.
They are connected in this place only by the pia-mater, which passes
from one to the other. But their internal faces adhere anteriorly for
the extent of three or four lines, by a small rounded cord, about a line
broad, and formed of gray substance, called the commissura mollis. Very
rarely the commissura mollis, (7) does not exist ;(8) hitherto we have
known it to be deficient only three times, nor is it common to find two
situated one above the other. (9)
Below there is no continuity of substance between the thalami optici. These two bodies are not united, except by the medium of the floor of the middle cerebral ventricle.
The external face is convex, and intimately united to the corpus striatum, but in such a manner, however, that we every where observe between the two eminences, medullary substance, which is the continuation of the cerebral peduncles. The posterior face is also convex, and always evidently divided into three rounded tubercles arranged in a triangle, and situated, one, the 'posterior ( iuberculum ganglii postici posterius , s. posterius superius ), upward and backward; the second, the internal corpus geniculatum ( corpus geniculatum internum , s. tuberculum posticum medium), downward and inward: finally the third, the external corpus geniculatum ( corpus geniculatum externum , s. tuberculum posticum inferius, s. externus ), still lower and externally.
The posterior tubercle is always larger than the two corpora geniculata, but more connected than they with the substance of the posterior cerebral ganglion.
The two corpora geniculata are sometimes equal in size, but usually the internal is larger. Their form is rounded.
Both are directly connected with the tubercula quadrigemina by medullary bands, which are sometimes blended, but are usually distinct and seperate from each other. The medullary band of the posterior tubercula quadrigemina, goes to the external corpus geniculatum, and that of the anterior to the internal corpus geniculatum. The first is much more constant and stronger than the second.
(1) At least we have always observed this. Sabatier has made the same remark,
( Anat ., vol. iii. p. 437.)
(2) Neurogr.. 1. i. c. ii.
(3) Obs. anat., c. iii. § 7.
(4) A dvérs. anat., 1. vi. c. x.
(5) Exp. anat., 1. iv. p. 163.
(6) Prolusio decerébro, ii. Leipsic. 1750, p. xi.
(7) Morgagni and Gunz, claim the honor of its discovery.
(8) Wenzel has known it to be deficient five times out of sixty-six, (De ccreb. p. 129). Gordon (p. 98) has always found it, and Sabatier almost always (p. 437.)
(9) Vicq. d’Azyr, p. 527. — Wenzel, Prodr. p. 15. — We also have observed this anomaly.
The two corpora geniculata are composed only of medullary sub stance externally. Internally they are formed by a mixture of white and of gray substance.
They are continuous downward with the root of the optic nerve.
The upper and posterior face of the optic bed, is covered with with a thin layer of white substance ; the internal of gray. Internally they present a mixture of white and of gray substance. Beside the medullary fasciculi from the tubercula quadrigemina, and which partly remain in the substance of the ganglion, partly also blend in its surface with the pineal gland, this body is' formed of several superimposed layers, the rays of which are directed from within outward, unite in the substance of the cerebral peduncle, and intimately interlace with it.
VII. CORPORA STRIATA.
§ 1774. The striated bodies , beds of the ethmoidal nerves , Ch., anterior cerebral ganglions , Gall, ( corpora striata , corpora striata antica inferiora, ganglia cerebri magna antica), (1) are two elongated, rounded, and flat bodies, formed almost entirely of a substance very gray externally, which occupy most of the lateral ventricles and the lower part of the anterior lobes. They are usually about two inches and a half long, and their greatest height is about one half of it. They are from eight to nine lines thick, and are highest and thickest anteriorly ; they gradually become thinner and lower posteriorly. The mean weight of each is about five drachms, and is to that of the optic bed as 5 :4. The weight and proportional size of these two eminences are, however, not always the same, as has been determined by Vicqd’Azyr and Gordon, with whose observations our own agree. Their weight is to that of the whole cerebrum as 1 : 29. Their greatest diameter is from before backward, and from within outward. They are nearly four lines distant from each other forward, and about two inches posteriorly ; because posteriorly the thalami optici and the tubercula quadrigemina exist between them, while anteriorly they are separated only by the septum, and the anterior part of the fornix.
Their upper and their internal portions are loose and unattached to a considerable extent ; this forms the floor, and the outer wall of the anterior horn of the large cerebral ventricle, has a conical form, is gradually elongated from before backward, where it is pointed, and describes in its centre a considerable curve, the direction of which is from before backward. After leaving the external edge of this loose part, the medullary substance is reflected from below upward at an acute angle, and forms the lateral and upper walls of the large cerebral ventricle.
(1) Magendie, Note sur les fonctions des corps striés et dès tubercules quadrijumeaux ; in the Journ. de phys., vol. iii. p. 376.
When cut from within outward, proceeding from this edge, we arrive only into the medullary substance of the hemispheres, but if the incision is made downward and a little outward, we come to the outer face of the corpus striatum, which makes an obtuse angle with the superior. This external face extends to near the entrance and the island of the fissure of Sylvius, from which it is only a few lines distant. Its upper part is straight, and formed from behind forw'ard bj^ a layer of medullary substance about four lines broad. The lower is convex in almost all its extent, composed of gray substance, and but loosely connected with the medullary substance of the posterior part of the anterior lobe, in the midst of which it is imbedded, so that the corpus striatum can easily be detached from this latter. Only the posterior part of the lower half of the external face is also straight and medullary, because the white band we have mentioned is reflected downward and forward : but at its most posterior part it again becomes gray, and here the gray substance, which is visible externally above, forms a tail which is inflected downward and forward in the same direction as the medullary substance, but does not however extend to the anterior large half of the external gray face.
The gray substance of the corpus striatum, seems then to be divided externally by a considerable layer of medullary substance, into an internal and upper half, and an external and lower.
The inferior face of this body is narrow and rounded. It is imperceptibly continuous with the internal and the external. Below it is blended with the medullary substance of the hemispheres, which gives it a whitish gray tint.
The lower part of the internal face is convex, and closely envelops the external face of the optic bed.
Horizontal, vertical, and oblique incisions, make us acquainted with the essential characters of the structure of the corpora striata. They demonstrate that these bodies are composed of three substances, one a deep gray, the second a light gray, and a third medullary, which form several alternate layers.
All these layers describe arches, the convex edges of which are turned upward, and the concave edges downward.
The medullary substance proceeds from behind forward, and from below upward, from the cerebral peduncle and the optic bed to the middle of the gray substance. At its entrance, which corresponds to the posterior extremity of the lower face of the corpus striatum, it extends its whole height ; but it soon divides into several fissures and superimposed layers, which are generally three in number, which go forward ; the lower two of these are much narrower and shorter than the upper. The latter, which also extends farther forward than the other two, does not proceed except to the upper and posterior part of the loose face of the corpus striatum, while forward and downward it is entirely enveloped by the gray substance which forms its anterior extremity. At the same time its breadth diminishes forward and downward, and it is interrupted by some gray substance both from before backward and from above downward, so that it is divided below into several layers of small white rays, some of which occur also between the third and second layer. This white substance, however, penetrates from behind forward, and from below upward, through the gray, and is continuous in every direction with the medullary substance of the hemispheres.
The light gray substance forms the middle and lower part of the corpus striatum : it is situated between the inferior and the first medullary layers, and likewise between this and the second, which it much exceeds in thickness. It occupies the smallest part of the corpus striatum.
Most of this body is formed of a deep gray substance, which is abundant particularly above, where it occupies the space between the second and third medullary layer, and forms the loose part of the corpus striatum, situated above and before this space.
The corpus striatum is then formed by alternate layers of white and gray substance ; all these layers are conical. Those of gray substance bulge forward, and those of white substance backward. All terminate in a pointât the opposite extremity, and interlace with each other.
The light gray substance which forms the middle and lower part seems to be formed by an imperfect separation of white and gray substance ; for the two lower layers of white substance are not so pure a white as the upper, which are contrasted with a deep gray substance.
The best method of becoming acquainted with the structure of the corpus striatum, is to cut and scrape its posterior and inferior part, and follow the medullary substance of the cerebral peduncle within it. The cerebral peduncle enters it from below upward, and from behind forward, and the medullary substance with which it is continuous is enveloped directly downward, inward, and outward, by the gray substance ; the corpus striatum is interrupted by this only in a small portion of its posterior extremity.
The medullaiy substance of the cerebral peduncle disappears at the posterior extremity of the corpus striatum, like the branches of a fan, in the form of fasciculi, which penetrate the gray substance in all parts, enlarge from before backward, and become thin from within outward. It sends outward and inward numerous radiating and pointed prolongations which expand in the gray substance, but do not extend to the circumference.
The gray substance of the corpus striatum is then divided in its whole extent by the white, which is continuous with the cerebral peduncle, into two parts, an external and an internal, which are blended together below, but not above. The white band of its upper face is the anterior edge of the medullary expansion which passes through it ; and the commencement of the medullary substance of the hemisphere formed by the white substance which passes through the middle of the corpus striatum.
As the medullary substance gives off in its course expansions which radiate in every direction, the corpus striatum ought necessarily to present internally the appearance described above, when cut transversely and longitudinally ; so that it much resembles the cerebellum, from which also the medullary substance disappears in thin layers, only there the gray substance which covers the latter, instead of having the same form, merely appears as a layer which is expanded uniformly over its surface.
VIII. TCENIA SEMICIRCULAR IS,
§ 1775. In the groove between the upper faces of the corpus striatum and the optic bed, is a narrow and prominent band, called the tœnia semicircularis ( stria cornea , s. terminalis , s. tœnia striata , s. geminum centrum semicirculare). This band is a little more than a line broad and is slightly prominent ; it commences before the foramen of Monro, near the anterior pillar of the fornix, with which it is always connected. It rarely terminates at the posterior extremity of the corpus striatum : it generally curves downward and outward, and disappears near the end of the roof of the descending horn of the lateral ventricle, where it communicates with the summit of the corpus fimbriatum in the descending hom of the great ventricle, and the most external fibres of the corpus fimbriatum and of the anterior commissure.
This band projects but slightly in the early periods of life : is whitish, and formed of longitudinal fibres, which raise in this place the inner membrane of the ventricle. It afterwards becomes, particularly on its inside, more prominent and brownish, and there is deposited on the surface of the medullary fibres primarily existing and which alone form it at the commencement, a more or less brownish layer, which is hard and solid, whence it is called the lamina cornea. This change ensues as the subject grows older, or cephalic affections exist ; so that it is not essential to the organization of the band. Tarin considers this substance as of a peculiar nature.(l) Vicq-d’Azyr regards it as the common gray substance.(2) Wenzel has attended particularly to its formation, and considers it as formed by an effusion of fibrin, and as it is developed, the adjacent membrane of the ventricles also thickens, and the number of the glands of Pacchioni increase.(3)
IX. ANTERIOR COMMISSURE.
§ 1776. The anterior commissure ( commissura anterior , s. magna, )(4) is a transvere, rounded, medullary fasciculus, which is slightly flattened from above downward, ami is a little thicker than the optic nerve : it is inclosed in a sheathe formed from the pia-mater, and is situated directly in front of the anterior peduncles of the fornix. Its anterior part is loose and exposed, but on the right and left the cord penetrates into the lower and anterior part of the corpus striatum ; is a little broader, becoming also gradually thinner ; goes outward, then backward, and a little downward, and thus describes an arch which is convex forward. This arch passes through the substance of the corpus striatum, but does not blend with it, and is situated in a special canal from which it is grooved. After leaving this transverse canal, it vanishes in rays, and terminates in the lower region of the fissure of Sylvius, and of the descending horn of the lateral ventricle, where it blends with the most external fibres of the corpus fimbriatum and tœnia semicircularis.
(1) Advcrs. anat., 1750, p. 2.
(2) Loc. cit., p. 430.
(3) Loc. cit., p. 82.
(4) Reil, Archiv, für die Physiologie . vol. xi., p. 8?.
Only the middle part of the anterior commissure is then perceptible,
and even this to a very slight extent without, if none of the cerebral
substance be removed.
This cord unites the anterior and inferior parts of the posterior lobe of the two hemispheres, and forms the anterior part of a ring which is closed posteriorly by the fornix, its appendages, and the tœnia semicircularis.
It is, however, very probably connected with the origin of the olfactory nerve, since it passes above the anterior cribriform plate, at a little distance from its roots, especially the external, and an undoubted relation between the development of these roots and that of the commissure, may be demonstrated in animals. Hence the origin of the optic and olfactory nerves very much resemble each other.
The structure of the anterior commissure is extremely curious, since it resembles a nerve, not only being surrounded externally by a thin neurilemmatic envelop, but is also formed internally by fasciculi of a very minute cellular tissue. The external and internal envelops do not disappear, except at the place where the commissure vanishes on leaving the corpus striatum.
X. CEREBRAL VENTRICLES.
§ 1777. The substance of the cerebrum is not perfectly solid. It incloses a considerable space, which corresponds generally in form to that of the external face, because it proceeds into all parts of this viscus, but its extent is much less: We may term this space generally the
cerebral ventricle ( ventriculus cerebri), or the central fissure ( fissura centralis).
The floor of this cavity is formed by that part of the cerebrum which corresponds to the anterior cords of the spinal marrow, and of which it is properly only a development. Its .sides and roof are formed by the parts superadded to these cords.
It begins at the posterior extremity of the upper face of the medulla elongata in the place where the posterior cords of the spinal marrow separate, and is here called the rhomboidal sinus, or the calamus scriptorius ; it continues then under the cerebellum, where it gives rise to the fourth ventricle, dilating in every direction : thence it contracts and passes under the tubercula quadrigemina, and forms the aqueduct of Sylvius ; it then again enlarges in every direction, principally, however, from above downward, between the thalami optici, where it forms the third ventricle , terminates anteriorly in this place in a cul-de-sac, but extends much to the right and left, and thus forms on each side the lateral ventricle.
The cerebral ventricle considered as a whole has the form of a cross, the anterior longitudinal arm of which is considerably shortened, while each of the lateral ones is divided into three arms.
All the different compartments communicate uninterruptedly with each other.
This cavity is not entirely closed. Its internal face, and consequently that of the cerebrum, communicates with the external in many parts, viz. backward, between the cerebellum and the medulla oblongata by the small transverse fissure ( fissura cerebri transversa parva ) ; and forward, between the corpus callosum, the corpus fimbriatum, the tubercula quadrigemina, and the thalami optici, by the large transverse fissure ( fissura cerebri transversa magna). These spaces, however, which are caused by the interruption of the cerebral substance, are filled by the arachnoid membrane and the pia-mater.
The parietes of these different cavities are smooth, and moistened with serum. Many anatomists(l) admit here only the choroid plexus, <md no special membrane. Bichat(2) and Wenzel, (3) on the contrary, whose opinion is more correct, have there found a special membrane, which is, according to the former, a continuation of the arachnoid membrane, while the latter regards it as a membrane of a particular character. The internal membrane of the first, second, third, and fourth ventricles is evidently continuous with the arachnoid ; but that which lines the fifth forms a closed sac. This circumstance, however, proves nothing against Bichat’s opinion, since the ventricle of the septum probably communicates with the others at first.
The inner membrane of the cerebral fissure is demonstrated with peculiar facility in youth, when the medullary substance above the lateral ventricles is carefully removed. It may be easily demonstrated also(4) in the ventricle of the septum or the corpora striata, in the posterior horn of the large ventricles, and on the floor of the fourth. It usually becomes thicker in hydrocephalus internus. Sometimes also it is very evident when serum accumulates between it and the cerebral substance. It can rarely, however, be separated completely, and some cerebral substance almost always adheres to its external face. Hence why many anatomists have termed it the medullary layer ( lamina medullaris).
(1) As Sœmmerring - , loc. cit., p. 48, § 59.
(2) Tr. des membranes, p. 216.
(3) Prodromus, § 8, p. 8. De cerebro, cap. viii. lntegumentum vcnlriculorum cerebri et partium in iis sit arum, p. 80.
(4) Wenzel, loc. cit., p. 81.
Very recently, also, Reil has applied the term epithelium to the union of this membrane with the shapeless substance which covers the parts of the cerebrum below it.(l)
Its thickness also varies in the normal state in the different regions where it is considered.
Of the divisions comprised by the cerebral ventricle, we have already described the rhomboidal sinus (§ 1729) : we have then only to examine the others.
a. Ventricle of the cerebellum.
§ 1778. The ventricle of the cerebellum , the fourth ventricle , the fifth ventricle ( ventriculus cerebelli, ven. quartus , s. quintus, Wenzel), (2) is triangular : its base looks downward and backward, and its summit upward and forward. It is continuous downward and backward with the rhomboidal sinus of the medulla oblongata. It penetrates backward and upward between the anterior and posterior extremities of the vermiform process in the substance of the cerebellum, and terminates there in a point. Anteriorly it passes under the posterior edge of the tubercula quadrigemina, and is continuous with the aqueduct of Sylvius. Its floor, which in the natural position of the cerebrum, constitutes the anterior wall, is formed by the upper face of the annular protuberance. Along the median line is a longitudinal groove about one line deep ; on each side of this rises a prominence which turns over from within outward.
From the anterior to the poetorior extremity of this floor a narrow and elongated blue place extends, which probably exists only in man ; this is formed of numerous minute blood-vessels, and is apparently connected with the origin of the auditory nerve(3).
The posterior and inferior wall is formed by the anterior and internal face of the posterior half of the vermiform process, and laterally by the posterior valve. The lateral walls are composed of the anterior and middle prolongations of the cerebellum. Finally, the superior is formed posteriorly by the posterior face of the anterior half of the vermiform process, and anteriorly by the anterior cerebral valve.
The fourth ventricle is open posteriorly, so that in this place the inner face of the cerebellum is continuous with the external by the small cerebral fissure.
(1) Archiv, für die Physiologie , vol. ix. p. 143.
(2) Desmoulins, Memoire sur le rapport qui unit le développement du nerf pneumogastrique à celui des parois du quatrième ventricule ; in the Journ. de phys.exp., vol. iii. p. 362.
(3) Loculi cœrulei in basi ventriculi quinti ; in Wenzel, loc. cit. vol. xvii. p. 168-169.— This blue place has already been described by Vicq-d’Azyr, in the Mém. de Paris, 1781, p. 585.
b. Aqueduct of Sylvius.
§ 1779. The aqueduct of Sylvius (aqœductus Sylvii,s. canalis emineniiez quadrigeminœ, ), is a very narrow channel which establishes a communication between the ventricles of the cerebrum and cerebellum. It is formed below by the u'fiper and convex face of the cerebral peduncles, on the sides and above by the tubercuia quadrigemina,and anteriorly by the posterior commissure and the pineal gland. It is continuous posteriorly with the fourth ventricle, anteriorly with the third, and also communicates in the latter place with the external face of the cerebrum.
The parietes of this canal present four longitudinal depressions, an inferior, two lateral, and a superior.(l)
The inferior is the most posterior, and is situated in the median line : it terminates the longitudinal groove in the floor of the fourth ventricle. The lateral are situated farther forward, become deeper towards the centre, and converge from behind forward. The superior, which corresponds exactly to the inferior, and which passes through the centre of the upper face, is the deepest : it is broader anteriorly and still deeper posteriorly.
We do not consider these depressions as particularly important, as Wenzel thinks them. We regard them only as the remains of the large ventricle covered in the fetus by the tubercuia quadrigemina.
c. Third ventricle.
§ 1780. The third ventricle (vent, tertius , s, processus fissurez me dianœ perpendicidaris, Gordon), commences at the anterior extremity of the aqueduct of Sylvius, and descends obliquely from behind forward. It is much larger than the fourth ventricle in man, while in animals the reverse is true. (2) Its form is very irregular, resembling an oblong square. Its length is much greater than its height, and it is only a few lines broad.
Its floor is formed by the gray substance situated before the cerebral peduncles by the mammillary eminences, finally between and before the latter, by the decussation of the optic nerves. Its anterior face is covered by the thin layer of gray substance situated before the decussation of the optic nerves, by the anterior peduncles of the fornix, and by the anterior commissure. Its upper wall or roof is covered by the body and the posterior peduncles of the fornix, and also by the posterior fold of the corpus callosum. Finally, its lateral walls are formed below by the internal, and above by the external faces of the thalami optici. Its lower face is the most irregular : considered generally, it descends from behind forward ; but we remark in it two culs-de-sac, the posterior of which is the commencement of the infundibulum, and the anterior is situated before the decussation of the optic nerves. Both of these depressions terminate in a point.
(1) Wenzel, Scrobiculi in canali corporum quadrigeminorum. Loc. cit., vol. rvi p. 166-167.
(1) Wenzel, loc. cit., cap. 21-22.
The fourth ventricle is imperfectly divided near its centre, posteriorly
into an upper and a lower half by the commissura mollis of the thalamic optici.
The anterior, superior, and inferior walls are perfect, but the lateral presents a space, or rather the anterior and the superior lateral walls are not united by cerebral substance. The middle and lateral ventricles of the cerebrum communicate by this space between the optic beds and the fornix. When the pia-mater and arachnoid membrane to which it gives passage are removed, it is quite large, but when these two membranes continue in place it is very small, and forms a very narrow opening between the lower anterior extremity of the thalamic optici und the anterior pillars of the fornix.
This opening is called the foramen of JMonro ( foramen JMonroi).
It is constant, except in certain pathological states. The impossibility of passing air from one of the lateral ventricles into the other, the permanent fullness of one of these cavities after the other has been opened and the fluid removed from it, and finally the difference sometimes remarked between the liquids accumulated in the two lateral ventricles,(l) have been adduced as arguments against its existence. But most of these phenomena may be explained by the falling of the vascular plexus across the opening, and also by the morbid adhesion with the edges of this latter, or of the edges themselves. (2) This latter cause is more probable, as most of the observations on which the above mentioned arguments rest have been made in circumstances favorable to a morbid adhesion. (3)
We must not confound with the foramen of Monro an opening admitted by incorrect anatomists in the septum lucidum, which does not exist ; when this is seen, it depends on the awkwardness of the anatomist, the bad condition of the cerebrum, or a morbid laceration.
In fact the third ventricle is continuous upward and backward with the aqueduct of Sylvius ; but it also communicates with the external under the posterior extremity of the corpus callosum, above and before the pineal gland, through a broad opening of which the pia-mater and the arachnoid membrane which penetrate into the cerebrum, contract the diameter, and which forms the central part of the large cerebral ventricle.
There is consequently in this place, about the centre of the encephalon between the cerebrum and cerebellum, a point where the external face of the cerebrum is continuous anteriorly and posteriorly with the internal by means of the third ventricle, and from before backward by the aqueduct of Sylvius.
(1) Portal, Sur une hydropsie particulière des ventricules latéraux du cerveau et sur la cloison qui les sépare ; in t he Mém. de Paris , 1770, p. 240.
(21 Monro, On the brain, Edinburgh, 1793, ch. 1.
(3) Virq-d' Aeyr, in the Mém. de Paris, p. 539.
d. Lateral ventricles.
§ 1781. The lateral , anterior , or large ventricles {yen. cerebri laterales , s. anterior es, s. magni , s. tricornes), {l) are situated in each hemisphere, on the sides of the corpus callosum, the fomix and the septum. They have an irregular are generally oblong form, being arranged so that their greatest length extends from before backward. Above they do not pass beyond the corpus callosum, and that part of the hemispheres into which the body extends. They form their roof, which must not be described as a separate and distinct part from the rest of the cerebral substance.
We may distinguish in it a middle part, and horns or curves {cornua).
The middle part proceeds directly from behind forward, and from above downward. It is continued inward by the septum lucidum and the corpus callosum, outward by the corpus striatum. Its floor forms most of the fornix.
1. Anterior horn.
§ 1782. The anterior horn is the smallest. It goes outward and downward. It is convex forward, and concave backward. It is situated between the anterior wall of the ventricle, and the anterior extremity of the corpus striatum.
2. Posterior horn.
§ 1783. The posterior horn, and the inferior or descending horn, are detached from the posterior extremity of the central part.
The posterior horn , the digital depression {fovea digitata ), terminates imperceptibly in a blunt point, goes rather directly backward, although it inclines also a little outward, and extends almost to about an inch from the posterior extremity of the hemisphere : its length, however, varies much.
The internal wall, and always that alone, presents in its inside a considerable eminence, called the digital eminence, the spur, the nail, the pes hippocampi minor {eminentia digitalis, calcar, unguis).{2) This eminence is very constant.
(1) Haase, De ventriculis cerebri tricornibus, Leipsic, 1789. — Rudolphi, De tentriculis cerebri, Gripswald, 1796.
(2) Morand, Obs. anät. sur quelques parlies du cerveau ; in the Mém. de Paris , 1744, p. 430.
We have always found it in the numerous brains we have dissected. Wenzel, out of fifty-one subjects dissected for this purpose, found only three in whom it was deficient
on both sides, and two where it appeared on one side only.(l)
This part bulges a little at its centre, and terminates posteriorly in a rounded extremity, which gradually becomes thinner. It is very constant in respect to its existence and situation : but its form and volume differ considerably, even in the two hemispheres of the same cerebrum.
Its form is sometimes narrow and elongated, and sometimes broader. It is generally smooth ; but it sometimes presents several transverse grooves, especially posteriorly, or is divided by a longitudinal groove into two halves, the upper of which is generally the larger.
Its size is usually in direct ratio with the development of the posterior horn. But there are exceptions to this rule, for a very small horn often incloses a very large eminence, while another which is very large may contain one which is hardly perceptible.
The structure of this eminence is generally homogeneous. It is composed of one circumvolution and a half: a small triangular groove arises from the bottom of one of the cavities between two adjacent hemispheres, on the inner face of the posterior cerebral lobe ; its summit is turned upwards, and its medullary substance is continuous with that of the inner face of the posterior horn. Its gray substance is blended with a layer of cortical substance, situated directly below the white substance which covers the internal face of the posterior horn, and forms with this latter the inner layer of the pes hippocampi minor. The medullary layer of this eminence is continuous upward with the white substance of the circumvolution above, as the gray substance also is continuous with the gray substance of the circumvolution which follows it.
This arrangement is easily recognized when we cut the pes hippocampi minor transversely.
There is then a resemblance in regard to form between the external circumvolutions and the pes hippocampi minor : this disappears or at least becomes smaller when the pia-mater is removed. (2)
3. Descending horn.
§ 1784. The descending or lateral horn , the largest of the three horns of the lateral ventricle, is convex outward and concave inward. It goes downward and forward in the external face of the cerebral peduncle, and occupies the lower, inner and anterior part of the middle lobe ; but it does not extend to its extremity, for it terminates half an inch behind it.
On its lower face are two large eminences, the cornu Ænmonis and the corpus fimbriatum.
(1) Loc. cit., p. 144-145.
(2) Wenzel, loc. cit., p. 146.
The cornu Ammonis or pes hippocampi ( cornu Jhnmonis , s. arieiis , s. pes hippocampi , proiubcrantia cylindrica , Ch.) is convex externally and concave internally, and rests on the lower face of the descending horn. It gradually becomes broader and higher backward than forward. Its anterior extremity, which is also that of the descending horn of the lateral ventricle and is considerably broad, curves inward and usually but not always presents from two to five longitudinal notches. The loose face of the cornu Ammonis is medullary, and longitudinal fibres are often very distinct in this layer of white substance, which is otherwise so thin that the gray substance which forms most of the protuberance is easily distinguished.
Sometimes* but rarely, we find a second eminence, which varies in length, at the side of and behind the cornu Ammonis so that it seems divided into two parts situated one above the other. This eminence is termed the collateral eminence of Meckel (eminentia collateralis JMeckelii), and seems to arise from suspended development.
On the inner and concave side of the cornu Ammonis is a narrow falciform medullary projection, which is perfectly parallel to this side, but less broad than it, and terminates in an inner loose and sharp edge on which the large choroid plexus rests. This is termed the corpus fimbmatum ( tcenia , s. fimbria). This body ceases about an inch before the large cornu Ammonis, and terminates imperceptibly in a circumvolution of the cerebrum.
At the side of the corpus fimbriatum, but farther inward and backward, consequently a little covered by it, but situated out of the descending horn, is another analogous and shorter body of gray substance which exists in the depression between it and the inner descending edge of the large lateral horn : this is the fascia dentata.
The loose edge of this small eminence is divided from above downward by numerous transverse incisions or folds into about twelve or fourteen small segments, which give it a waved appearance ; these disappear on removing the pia-mater.
A transverse incision across the parts within the descending horn shows that the cornu Ammonis is covered on its upper and lower faces by a medullary layer, which terminates above in the corpus fimbriatum, and which penetrates farther inward below and is reflected in the medullary substance of the lower face of the horn.
Next to this medullary layer comes another of gray substance which is much thicker, being as thick as that on the surface of the cerebrum ; this exactly covers the preceding, and is continuous with the cortical envelop of the encephalon. The upper face, which is farther from the median line, and consequently forms the outer part of this gray layer, is the fascia dentata. The internal is continuous with the gray substance of the inner face of the lower part of the posterior lobe of the cerebrum.
Between this internal and this external part a thinner medullary layer is interwoven ; this enlarges above where it is loose and unattached.
These parts are then evidently similar to the corresponding halves of two adjacent circumvolutions, between which a medullary layer penetrates instead of the pia-mater alone, and which is covered internally only by a very thin medullary layer.
The thin medullary layer which covers the gray substance is continuous in all parts with the rest of the white substance, but that which exists before the lower face of the cornu Ammonis is always separated in every part from that opposite, which covers the upper face of the eminence and is inflected only at the upper part to go and meet it. If these adhered, this lower layer and this inner layer of gray substance of the cornu Ammonis united to the floor of the descending horn of the lateral ventricle and to the substance below, would form a complete circumvolution.
The medullary envelop of the cornu Ammonis is continuous with the posterior part of the corpus callosum, and partly also with the posterior pillar of the fornix. The whole corpus fimbriatum passes into the latter.
The lateral ventricles are inclosed and enveloped by cerebral substance in most of their extent, which is uninterrupted.
This is true particularly of the anterior horn and the posterior horn. On the contrary, the middle region and the lower horn are interrupted in a considerable part of their extent, since the fornix and the corpus fimbriatum are not united to the adjacent parts. From this arrangement it follows that the middle region communicates from above downward and from without inward with the third ventricle : that the descending horn is in relation with the external face of the posterior cerebral lobe, and consequently that there is between the corpus fimbriatum and the posterior part of the optic beds, a space which forms the two sides of the large cerebral fissure, with the central part of which it is blended internally. If we then separate the edges of this space which is filled by the arachnoid membrane, and also by the pia-mater and the cellular tissue, we arrive at the descending horn of the lateral ventricle and the third ventricle without cutting the cerebral substance ; thus by slitting the roof of the descending horn from within outward, wecan reflect from behind forward all the posterior part of the hemispheres with the corpus callosum and the fornix.
II, TEXTURE.
§ 1785. The cerebrum is the developed and expanded anterior part of the spinal marrow.
The two lateral cords of this anterior part intercross and form above the decussation, the pyramids, which project very distinctly on the lower face of the medulla oblongata.
At their sides is a narrower fasciculus, the fibres of which divide below the olivary bodies into an anterior and a posterior layer, which surround these eminences, above which they again unite to enter the annular protuberance.
The third fasciculus is the largest. It is situated inward and backward at the side of the preceding. It forms the floor of the calamus scriptorius and of the fourth ventricle, where it is covered by the gray substance.
These three fasciculi, situated one above another, and separated by the gray substance and also by the transverse fibrous layers which arise from the lateral prolongations of the cerebellum, pass through the annular protuberance.
They unite in front of this protuberance, and form the cerebral peduncle, of which the pyramids form the outer and lower side, and the two other cords the inner and upper side.
The formation of the cerebral peduncle by longitudinal layers, the edges of which converge from without inward, is more evident in the lower face than in the upper, the lower and convex face of which rests on the upper and concave face of the former. We may then oppose the upper and the lower parts to each other, and call the former the base and the latter the cap (Haube), of the cerebral peduncle. (1)
The three fasciculi produced by the division of each lateral anterior cord in the medulla oblongata, still continue separate in the cerebral peduncle and the cerebrum.
It is most convenient to describe the middle fasciculus first, because it terminates the soonest.
This fasciculus proceeds from within outward, and divides in the posterior part of the pons Variolii into two fasciculi: one proceeds below the black substance of the cerebral peduncle ; the other, termed the knot, (2) goes upward, is seen externally between the anterior and middle prolongations of the cerebellum, and proceeding along the outer face of the former, goes obliquely to the posterior tubercula quadrigemina. It divides at the outside of the latter into two arms ; one goes forward upon the external corpus geniculatum, and into the optic bed : the other proceeds transversely inward, disappears below the tubercula quadrigemina, forms the roof of the aqueduct of Sylvius, and blends forward with the posterior commissure, backward with the middle cord which goes from the posterior tubercula quadrigemina to the large cerebral valve.
The lower anterior fasciculi of the anterior cord of the spinal marrow, which correspond to the pyramids in the medulla oblongata, and
(1) Reil, Archiv, für die Physiologic, vol. ix. p. 150.
(2) Reil, Archiv. für die Physiologie, vol. ix, p. 505.
which are the direct continuation of them, form the lower part of the cerebral peduncle, and go from below upward and from within outward below the optici thalami.
The upper and posterior, which are larger, proceed directly towards the posterior part of the optic beds.
Both unite, leave the optic bed outward and the fibres of the layer forward, which proceed from within outward, and pass above them ; at the anterior and external _side of the protuberance, these cords and fibres interlace and give rise to a kind of suture, expanding in every direction. The external layers are reflected backward, and do not pass through the optic bed.
Hence it follows, that in each of the cerebral hemispheres there is a semicircle, the concavity of which is turned toward that of the opposite side, while it is convex .externally, and which like the' cerebral peduncle is composed of layers or rings which are directed from above downward. These rings expand in every direction like the sticks of a fan. Reil terms this the corona radiata. The posterior and middle rings, which are fewer, soon go outward and backward, and form most of the posterior and middle cerebral lobes. The anterior are more numerous, first pass through the corpus striatum, and then form the larger anterior lobe of the cerebrum.
The circumvolutions are formed of two strata of layers which are fitted to each other ; they are united by serum effused in the ventricles, and may be more or less easily detached in the cadaver by compression, or by hardening the brain in different modes.
III. WEIGHT.
§ 1786. The cerebrum generally weighs three pounds, apothecaries' weight. Its proportion then to the cerebellum is as 8 : 1, and to the medulla oblongata as 72 : 2.
IV. CONSISTENCE.
§ 1787. In regard to consistence, it differs only from the annular protuberance, which is much harder.
CHAPTER III.
ENVELOPS OF THE CENTRAL PART OF THE NERVOUS SYSTEM.
§ 1788. The central part of the nervous system is, as we have already stated, (§ 176) surrounded by several superimposed membranes. For a long time three have been admitted, an internal, the pia-mater , a middle, the arachnoid, and an external, the dura-mater. But the ancient anatomists, and Lieutaud, Sabatier, and Chaussier among the moderns, considered the internal and middle as forming but one, called the meningeal ( meningina ), which is composed of two layers distinct in the vertebral column, on the cerebellum and lower face of the cerebrum, but intimately blended in all other parts.
We must admit as correct, that the two inner membranes are very intimately connected in several parts, that they must be considered as forming only one : for we cannot demonstrate in the upper and lateral parts of the surface of the cerebrum, the two layers mentioned by Chaussier, and which he says are united by a very short cellular tissue. The pia-mater is alone visible in these parts.
In fact it is asserted that the arachnoid membrane extends like a bridge on the circumvolutions, while the pia-mater penetrates into these cavities, and that the former membrane may be easily separated by inflation : but we have always observed in repeating this and similar experiments, that the pia-mater was raised, and not a membrane distinct and separate from it.
It does not follow, however, that we must admit that the two inner meningeal membranes are the same. On the contrary, the following arguments exist against this opinion :
1st. Difference of structure. The arachnoid membrane is whitish, semitransparent, and destitute of vessels ; the pia-mater is transparent and formed entirely of blood-vessels united by cellular tissue.
2d. Difference in the arrangemement. The two membranes are entirely distinct in several parts, and the arachnoid membrane is never found except on the surface, while the pia-mater penetrates deeply, and every where attends the surface of the cerebrum and spinal marrow.
3d. The structure of the fetus. In the cerebrum we can easily sepaparate the arachnoid membrane from all the encephalon.
4th. Difference of pathological changes. The arachnoid membrane becomes harder and thicker : false membranes are formed by exudation from it. The pia-mater generally only receives more blood, and consequently assumes a redder tint. We must admit, however, that the pia-mater in several parts, particularly internally, sometimes experiences those changes regarded as belonging exclusively to the arachnoid membrane.
As the latter blends in a single membrane with the pia-mater within the skull, so too it unites with the dura-mater in the skull and vertebral canal so intimately, that it is very difficult and almost impossible to separate them.
ARTICLE FIRST. OF THE PIA-MATER.
§ 1789. The pia-mater ( tunica cerebri vasculosa , s. propria , s. pia mater) is a thin membrane formed of mucous tissue, in which the large vessels which go to or return from the central part of the nervous system expand. Its unattached upper face is smooth and moistened with serum. The internal, on the contrary, presents inequalities which arise from numerous villosities, greater or less branches of vessels, which attach it to the surface of the brain and spinal marrow. It not only lines the external face of the central portion of the nervous system, but also penetrates in several parts within it, where it conducts those vessels which carry the blood, and receives those which take it up again. We may then divide it into external and internal. These two sections of the membrane present considerable and constant différences in different regions of the central portion of the nervous system.
I. PIA-MATER OF THE SPINAL MARROW.
§ 1790. The pia-mater of the spinal marrow increases very much from above downward in thickness, hardness, and solidity. It exactly envelops the spinal cord in all its extent, so that when cut across, the medullary substance rises above the surface of the incision. Its color is yellowish white. Its external face is smooth and entirely loose : it is in contact with the arachnoid membrane, from which it may be easily separated by blowing air between the two membranes.
At the lower extremity of the spinal marrow, the pia-mater becomes ^ simple filament, which descends between the nerves of the cauda equina to the lower extremity of the spinal dura-mater, with which it is blended at its termination.
Its internal part is formed by an anterior and a posterior prolongation, of which the former is larger and more apparent. These two prolongations extend from before backward and from behind forward, into the two middle fissures, and are arranged like the neurilemma as we have already remarked (§ 160).
II. PIA-MATER OF THE ENCEPHALON.
§ 1791. The pia-mater of the encephalon should necessarily be distinguished into internal and external , from the manifest differences in its form, presented within or on the outside of the organ.
a. BXTERNAL PIA-MATER.
§ 1792 .The external pia-mater of the cerebrum, the cerebellum, and spinal marrow, is intimately adapted to the surface of these three sections of the central part of the nervous system, and penetrates into the greatest as well as into the smallest cavities to their bases, so that it represents exactly the external form of the parts. It does not leave the surface of the brain except in a few points. Thus in the calamus scriptorius, it passes from side to side, forming a transverse bridge sustained by a small medullary prominence, which is continuous forward at an acute angle with the pia-mater which covers the posterior face of the cerebellum. So too the thin layer which closes the third ventricle forward and downward before the decussation of the optic nerves, is often replaced by the pia-mater only, which extends like a bridge from one hemisphere to the other. These prolongations which penetrate into the superficial cavities, particularly into the grooves of the cerebellum and the anfractuosities of the cerebrum, are real folds, (1) since each is composed of two layers, which are united more intimately at the entrance of the anfractuosities than in their course and at their base, which must be attributed partly to the large vessels which pass in this place to the surface of the encephalon, so that they are easily insulated from each other when these vessels are destroyed.
The external pia-mater is continuous with the internal, wherever the external face of the encephalon is itself continuous with the internal, that is with that which forms the parietes of the ventricles. Thus these two membranes unite in the fourth ventricle, through the posterior cerebral fissure, and in the aqueduct of Sylvius, and also in the lateral ventricles by the anterior cerebral fissure.
We frequently observe on the external pia-mater, rounded and generally soft corpuscles, which are yellowish white, and collected in several masses; these are generally termed the glands of Pacchioni ( Gl . Pacchioniance)(2 ) but Bichat terms them the cerebral granulations {granulationes cerebrales). These corpuscles are situated principally along the centre of the superior longitudinal groove, especially at the orifice of the veins which enter into it. Placed on the external face of the pia-mater, they pass through the dura-mater, and even enter into the cavity of the sinus, where they are covered by the inner membrane of the venous system. They are generally arranged in several groups, but so that the different corpuscles of one must rest on a common base. They vary much in number and size ; their structure is entirely homogeneous. As they are found particularly in the latter periods of life, as they never exist before, as they are not numerous except in per (1) Soemmerring - , De cerebri administrationibus anatomicis , vasorumque ejus habitu ; in Münchner Denkschriften for 1808, p. 66, 67.
(2) Pacchioni, Epist. phys. anat.; in Opp. omn., Rome, 1741, p. 125.
sons often afflicted with diseases of the head, and as they are not observed particularly in any animal, we have reason to think them mere morbid formations resulting from the frequent rush of blood towards the brain.(l)
Still in no case do they deserve to be called glands. They have no excretory canals which carry a fluid secreted by them between the dura-mater and the pia-mater, or between this latter and the encephalon, or even within the cerebral ventricles, as Pacchioni asserts.
B. INTERNAL PIA-MATER.
§ 1793. The internal pia-mater differs from the external in its texture and form. In fact it is thinner and of a more delicate tissue. It adheres more intimately to the parts which it lines, and is, in fact, blended with them, as are the serous membranes with the articular cartilages upon which they pass. The portion which does not cover the surface of the ventricles, gives rise to the choroid plexuses ( plexus choroidei ). These latter are composed essentially only of that portion of the internal pia-mater which is loose and entirely unattached in the ventricle. They form an immense number of folds which intercross, and are arranged in several parallel longitudinal series. They are situated on the internal pia-mater, very near its union with the external, and on the edges of the fissures by which the external and the internal faces of the brain communicate. We find them in every section of the cerebral fissure, or of the cavity of the ventricle generally. Are not the folds there observed so many marks of the prolongations of the external pia-mater, which enter into the grooves of the external face, or rather do they not result from the collapse of the choroid plexuses after the early periods of life, when they are larger and are situated in the cavities of the encephalon, which are much more extensive ?(2)
The branches of the veins from the inner face of the cerebral substance, unite in the choroid plexuses, and the arteries which penetrate into this same substance ramify in them,
(1) Wenzel, loc.cit., cap. i. Corpusculain e.vtcriori meniuge et infra eamabs utroquef aids latere. — Portal (Cours d’an at. med., vol. ii.) has already doubted the glandular nature of these corpuscles, and maintained they were only cellular tissue filled with adipose substance (p. 10). In regard to similar bodies found in the choroid plexuses, he says, “ (p. 44) as these glandular bodies appear only in disease, are they not concretions which are formed in the cellular tissue of the pia-mater, varying in size and hardness?”
(2) Desmoulins thinks (Journal dc physique, Feb. 1821) the choroid plexuses and telæ arise, from the fact that the internal pia-mater, after deposing concentric layers of white fibres, finally contracts. From this contraction or obliteration, result the concave internal surfaces of the folded membrane of the hemispheres, and the formation of the white and solid nucleus known as the oval centre. Tiedemann has already expressed, with slight modifications, the same opinion as Meckel. Desmoulins thinks that the membrane of the hemispheres gradually folds to produce the circumvolutions, and that the pia-mater contracts proportionally in the cavity of the ventricles. He admits, consequently, the correctness of Gall’s process for unfolding
We also find there some corpuscles corresponding to the glands of
Pacchioni of the external pia-mater, in the same cases as the latter,
and most generally at the same time as they.
Another very common pathological change of the choroid plexuses, is the occurrence of serous cysts, which are there accidentally developed.
Ï. CHOROID PLEXUS OF THE FOURTH VENTRICLE.
§ 1794. The choroid plexus of the fourth ventricle (plexus choroideus ventriculi quarti) begins on each side at the side and on the lower Face of the root of the fourth lobe of the cerebellum, and is situated between it, the anterior edge of the monticule, the facial, the auditory, the glosso-pharyngeal, the pneumo-gastric, and the accessory nerves. Thence itgoes transversely on the anterior part of the calamus scriptorius directly below the monticule, between it and the restiform body, and approaches that of the opposite side. The two plexuses united by a narrow band of the pia-mater then divide each into an anterior and a posterior branch. The posterior branches ascend in the posterior groove of the cerebellum, along the anterior part of the internal face of the monticule, become pointed, blend together, and terminate at the upper extremity of the uvula. The anterior, which are shorter, approach each other from before backward, and are blended together on the nodule of Malacarne.
This plexus receives from below upward the ramifications of the basilar and vertebral arteries and from above downward, and also on the sides those of the veins which arise from the inner face of the cerebellum.
The glands of Pacchioni are perhaps more common hi this part than in the choroid plexuses of the cerebrum.
II. CHOROID PLEXUSES OF THE CEREBRUM.
§ 1795. The internal pia-mater of the cerebrum begins at the large cerebral fissure. It forms a layer which is much broader in the centre than on the sides, but more folded, on the contrary, on the sides than in the centre.
the brain, and thus explains the nature of what the latter terms the mucous neurilemma of agglutination of the internal surfaces, saying that it is the residuum of the
pia-mater, which sometimes becoming permeable to the blood, can re-establish in
greater or less portions, the primitive liberty of the internal surfaces. We only mention this assertion, without disputing it, as it seems easy to do with advantage. It is
connected with another opinion of Desmoulins, that the development of the intellectual faculties is in direct ratio with that presented by the surface of the folded membrane of the hemispheres, consequently in a ratio with the number and depth of the
circumvolutions. ( Sur le rapport le plus probable entre V organization du cerveau et
ses fonctions , in the Journ. compq des de Tnéd. vol. xiii. p. 206). f . T.
It goes inward and forward from the posterior edge of the corpus callosum, the internal face of the posterior lobes, the cerebral peduncles, the tubercula quadrigemina, and from the middle anterior portion of the cerebellum, is continuous on one side with the external pia-mater which covers these parts, and envelops on the other the pineal gland, and proceeds forward and inward under the posterior edge of the corpus callosum and of the fornix. It thus forms a triangular layer, the base of which looks backward and the summit forward. The internal face of this layer is united by its lower part with the upper face of the optic bed, and by its upper with the lower face of the fornix. Hence these faces are connected so intimately, except at the lower part, for the space of about two lines deep and one high, that the third ventricle is perfectly closed at its upper part, and is separated outward from the two lateral ventricles.
This portion of the internal pia-mater may be termed the choroid web ( tela choroidca , Vicq-d’Azyr.)
It is continuous outward and backward with the choroid plexuses of the lateral ventricles.
These plexuses which arise from the opening through which the two lateral ventricles communicate, proceed from behind forward and from within outward on the lower face of the centre of each ventricle, and afterward descend from behind forward in the lateral horn, on the corpus fimbriatum and the cornu Ammonis. A slight fold attaches them in all their course to the lateral edges and the anterior edge of the fornix and the corpus fimbriatum which is detached from it. Their form then exactly represents that of the descending horn, into which they penetrate to its anterior extremity, and the lower face of which they cover in great part. At their anterior extremity, that is, at their origin, in the communication open between the two lateral ventricles they are very narrow, but they gradually enlarge from before backward, and finally become considerably broad.
Their breadth, however, does not increase from their origin to the lower extremity of the lateral horn. Their broadest and thickest part corresponds to about their centre, that is, where instead of internal they become external. There, in fact,, they form a kind of button, which has been remarked by Vicq-d’Azyr,(l) and has been admitted by Wenzel. (2) The vessels, particularly the veins, are there much larger and also more tortuous than in the rest of the plexus : the internal piamater which unites them also forms there more numerous folds.
(1) Loc. cit. p. 541. “ The region in which the plexus is thickest, is that where it
curves backward, at the level of the posterior prolongations of the lateral ventricles.” Vicq. d’Azyr has also described the structure of the choroid plexus, and this figure of it resembles that given by Wenzel.
(2) Loc. cit. n. ix. Animadv. peculiarem quand, proprietatem plexus choroidei, etc. Proprietas qucedam ratione morborum , ut nobis videtur, notatu digna ab aucloribus prœtervisa.
The choroid plexus also, when otherwise perfectly healthy, is rather more disposed in this place to morbid changes, such as thickening, opacity, and more or less abundant granulations which vary in form and size, and which probably arise, at least in part, in the folds of the plexus, but which are also developed on the surface of these folds. (1)
The greater development of the choroid plexus in this place depends particularly, and even solely, on the origin at that part of the posterior horn, which receives no special choroid plexus.
Besides this common choroid plexus, we sometimes find in the lateral ventricles a smaller and anterior plexus, which is situated on the corpora striata. This communicates with the veins which proceed between the anterior and posterior cerebral ganglions, and with those which arise from these eminences. (2)
On the contrary, we constantly find two small choroid plexuses, those of the third ventricle, which extend from before backward, from the anterior extremity of the lateral choroid flexus to the circumference of the pineal gland, separate from each other in this course, are attached to the lower face of the tela choroidea, gradually increase in size and receive the vessels of the third and fourth ventricle.
All the sections of the general ventricle of the encephalon include then the choroid plexuses which communicate by the internal piamater and the cerebral vessels, and which are most generally found more or less precisely in the same state in the same subject.
ARTICLE SECOND, OF THE ARACHNOID MEMBRANE.
§ 1796. The arachnoid membrane (mem. arachnoidea, s. mucosa ), the second envelop of the spinal marrow and encephalon, is delicate, thin, semitransparent, whitish, and perfectly homogenous in structure. We have not as yet been able to discover in it either vessels or nerves.
It is very distant from the preceding in the vertebral column and in the lower part of the skull.
It surrounds the spinal marrow, like a sac which is much larger than this cord, which is attached to it only by some distinct filaments of cellular tissue. It begins at the lower extremity of the vertebral column, and gives a general envelop which covers the origin of all the nerves in the spinal canal until they leave this cavity. We may then separate it very much from the spinal marrow bjr blowing in air, or by any analogous process.
(1) Vicq-d’Azyr has also made this remark; he expresses himself very strongly against the glandular nature of this body,
(2) Vicq. d’Azyr, p. 540.
It is also intimately united with the dura-mater in the place where this membrane forms narrow canals which receive the nerves before they leave the vertebral canal, and where the slips of the ligamentum dentatum are attached to its surface.
It proceeds from the spinal marrow to the encephalon, enlarging very much. It adheres to the lower and middle portions of the cerebrum, and also to the posterior part of the cerebellum and to the lower face of the medulla oblongata very loosely and by long distinct bands of cellular substance, passes like a bridge from the spinal marrow to the posterior part of the cerebellum, and from one lobe of the latter organ to another, consequently fills the space between them, closes the common cerebral fissure posteriorly, below and on the sides, is reflected from the annular protuberance on the floor of the third ventricle towards the decussation of the optic nerves, with which it is intimately united, as also with the nerve itself ; then arrives at the lower face of the anterior lobes, and connects both these two lobes and also the central part of the posterior, on which it extends on each side on leaving the annular protuberance. It also forms a bridge which proceeds on the fissure of Sylvius, between the posterior and anterior lobes.
All the veins and nerves which come from the encephalon, and also the arteries which go to it, are covered by prolongations of the arachnoid membrane until they emerge from, or enter the cranium.
But the places we have mentioned are the only ones where it is so slightly attached to the subjacent pia- mater that it may be considered a separate and distinct membrane. In every other part, even where it passes from one circumvolution to another, proceeding over the anfractuosities, it is so intimately united with the pia-mater that, however carefully we may attempt to raise it, particularly by the common mode, that of insufflation, this membrane is always detached with it from the surface of the cerebrum.
§ 1797. From the idea generally formed of it, the arachnoid membrane forms only a single layer, which covers the outer face of the spinal marrow and encephalon ; but it rarely extends farther, and has a more complex course. In fact, it is reflected from all the places through which the nerves and vessels pass upon the dura-mater, the internal face of which it covers, and also penetrates within the encephalon through the large cerebral fissure.
The first proposition is perfectly demonstrated either by dissecting the arachnoid membrane and the dura-mater in the normal and abnormal state, or by analogy. The brilliant and smooth appearance of the inner face of the dura-mater favors it, since the parietes of the pectoral cavity, the abdominal cavity, and the pericardium, depend for this character on the presence of serous membranes, which after directly covering the surfaces of the organs, leave them to be reflected externally. This external layer of the arachnoid membrane is fitted to the inner face of a fibrous membrane like the serous tunic of the pericardium, the peritoneum and the two pleurae in many places, the synovial membranes, &c. That the shining appearance of the inner face of the dura-mater does not depend on this membrane is proved by the fact that the interior of the canals it furnishes to the nerves out of the arachnoid sac is very uneven.
When we examine the dura-mater either from without inward or from within outward, although all the external layers seem formed of fibres and of a very complex texture, we may always detach to a greater or less extent an internal layer, which is thinner than the others, and has not a fibrous appearance : this may be easily proved hr the early periods of fife. This internal layer is sometimes separated from the others by a congestion of pus between it and the duramater it hnes.(l)
The arachnoid membrane not only covers the surface of the cerebrum, but also penetrates within this organ. The place where it enters is between the anterior extremity of the upper face of the cerebellum and the corpus callosum, in the place where the portion of this membrane which covers the cerebrum unites to that of the cerebellum, without forming however a simple sac. The connection seems on the contrary to be interrupted by a rounded opening in this place, in the circumference of which the glands of Pacchioni are generally situated in old persons, and which give passage to the veins which arise from the ventricles of the cerebrum : but this opening is the commencement of the inner part of the arachnoid membrane, for it leads to a canal which passes on the pineal gland and extends from behind forward on and between the anterior edges of the optic beds, and below the fornix to the anterior extremity of the third ventricle. This canal surrounds the venous trunks which return from the middle and lateral ventricles. It is every where perforated for the branches which go to it. Its external face is connected with the adjacent parts of the cerebrum only by slight adhesions, and is also attached to the veins by distinct filaments. It terminates at the foramen of Monro. Thence it continues, uniting intimately to the pia-mater, with the internal membrane of the ventricles, which in the normal state is much thinner than it, but which in the pathological state, in; inflammation and hydrocephalus, thickens, becomes opaque, whitish, so that then it is still nearer to it and. to the outer part of the arachnoid membrane.
The arachnoid membrane most resembles the serous membranes in its form, texture, secretions, its ana-tomical relations with the encephalon and spinal marrow and with the dura-mater, and in its diseases, as thickening, increase of its secretory power, whence result congestions of serum, adhesions between contiguous surfaces or the formation of accidental membranes. It is almost exactly like them. Gordon then is wrong in supposing that the analogy between its texture and that of the serous membranes is not proved, and that we must consider it as a separate organic tissue different from all others.
(1) Vicq-d’Azyr, in the Mém. dc Paris , 1781, p. 497.
All the facts we have adduced authorize us to arrange the arachnoid membrane and the dura-mater in the class of sero-fibrous membranes. It however is important to remark, that these two membranes are very intimately united with each other, and that the difference observed between them in the adult does not exist in the fetus, where we find, instead of the dura-mater, only a single thin transparent membrane destitute of fibres, and having all the characters of a serous membrane. But there we evidently have a new fact in support of our opinion in regard to the nature of the arachnoid membrane. At first only the inner layer of the dura-mater is formed ; afterward it is changed externally into a fibrous tissue, or this tissue is developed between it and the bones.
ARTICLE THIRD.
OF THE DURA-MATER.
§ 1798. The dura-mater ( dura meninx), a fibrous membrane, is the most external envelop of the spinal marrow and encephalon. It forms a sac closed in every part, which has the form of these two organs. Its external face looks to the inner face of the spinal canal and the skull ; the internal is turned towards the outer face of the arachnoid membrane. This latter is smooth in every part.
The vessels of the spinal portion of the dura-mater arise from the vertebral, the intercostal, the lumbar, and the sacral arteries : those of the cranial portion from the internal maxillary artery.
J. SPINAL DURA-MATER.
§ 1799. The spinal portion of the dura-mater differs in several respects from the cephalic. It forms a very long canal, terminated at its lower part in a cul-de-sac, which occupies the whole spinal canal, gradually enlarges from above downward, but terminates in a blunt summit at the lower extremity of the sacrum. This sac is narrower than the spinal canal, to which it adheres, principally on the sides and posteriorly, only by a very loose cellular tissue, which contains, especially at its lower part, an abundance of substance similar to fat, of a reddish yellow color. It is united anteriorly to the posterior ligamentous envelop of the vertebral column much more intimately.
The two faces of the spinal dura-mater are smooth. It is not only longer, but much broader than the spinal marrow. Outwardly it gives to each spinal nerve a sheath which accompanies it to beyond the intervertebral foramen, enlarges a little in this place on account of the ganglion of the posterior root, and gradually terminates in the external cellular tunic of the nerve.
It is very evidently formed of longitudinal fibres which are more regular but less distinct than those of the cranial portion, and it is thinner than the cerebral dura-mater.
II. CEREBRAL DURA-MATER.
§ 1800. The portion of the dura-mater which corresponds to the encephalon, is attached to the internal face of the skull by numerous small ramifications of vessels which extend from it to the bones : its external face is corrugated. It adheres very strongly to the skull at its lower part : its lateral and upper faces are connected with the sutures more intimately than with the other parts of the cranium.
The arteries and veins proceed on its external face in the slight depressions which they exactly fill, and also project above its surface.
There are but few fibres visible on its external face. The centre of its upper part presents some which are irregular, flat, have a transverse direction, and intercross.
We distinguish through the dura-mater the vessels of the pia-mater, and also the elevations and depressions of the external face of the encephalon.
The inner part of its upper face presents at intervals along the large longitudinal sinus, and some lines from this venous canal, some broad and some narrow openings which are seen principally in the region of the sinciput.
Internally it presents in all its extent a fibrous texture much more distinct than that of the spinal portion. We may divide the fibres seen there into two layers. The external follow a longitudinal direction for all the extent of the membrane, and are arranged .very compactly ; the internal are placed on the preceding, to which they generally adhere but slightly, and are much more separated from each other ; they are particularly apparent and very numerous at the upper part, while they gradually disappear at the lower.
Although the dura-mater is usually considered as divided into several layers, between which the venous sinuses proceed, and is composed of two folds, and although we can in fact divide it into two layers, still this separation is purely artificial, always excepting the serous layer ; we can never form them except by destroying the tissue, and we may at pleasure diminish or increase the number of the layers.
The cerebral dura-mater principally differs in its arrangement from the spinal by the following characters :
1st. It does not form a single sac but a cavity which is divided into several partitions by different prolongations which it sends inward. These prolongations are in direct ratio with the development of the encephalon, as they divide the cavity of the skull into compartments destined to receive the principal portions of this organ. We number three of them, a transverse and two longitudinal. They have this in common, that at their external edge, which is connected with the internal face of the skull, they divide into three layers, the external of which continues to follow the direction of the common sac of the duramater, while the two internal converge inward and are soon blended in a single layer which terminates in a loose internal edge. Besides the external edges, the internal edges, and the faces of these prolongations, are continuous with each other, and they may be described under the common name of the crucial prolongation of the dura-mater ( processus dura matris cruciatus), the branches of which extend to the right and left, upward and downward, and forward and backward.
The transverse prolongation is the tentorium of the cerebellum , the transverse septum ( tentorium cerebelli). Its form is nearly semicircular. Its posterior, convex, and internal edge, which is thelongest, arises from the transverse branches of the cruciform ridge of the occipital bone, and from the upper edge of the petrous portion of the temporal bone. The anterior which is much smaller and concave, is loose : it forms the posterior and lateral parts of an opening which is closed anteriorly by the basilar portion of the spheno-occipital bone, and is attached on each side by two separate points to the anterior and posterior clinoid processes, between which it covers on both sides the sella turcica.
The cerebellum and the medulla oblongata are situated under this tentorium, which completely separates from the rest of the skull, excepting only from the anterior opening, the posterior and inferior part destined to receive it.
The central portion of the tentorium is continuous upward and downward with the two longitudinal prolongations, the falx of the cerebrum, and the falx of the cerebellum, both of which are situated on the median line, and the external edge of which is convex and broader than the other, and is attached from before backward to the external edge of the dura-mater, while the internal is concave, sharp, and loose. These prolongations separate the right and left portions of the cerebrum and cerebellum.
The falx of the cerebellum , the median septum of the cerebellum ( falx cerebelli ), is situated posteriorly between the two hemispheres of the cerebellum, extends from the centre of the posterior edge of the tentorium of which it makes a part, and from the inner occipital protuberance to the centre of the posterior edge of the large occipital foramen. It descends along the internal occipital crest, gradually contracts and divides at its lower extremity into two small lateral folds which extend forward.
The falx of the cerebrum, or the large falx, the longitudinal fold of the meninx, {falx cerebri, s. processus falciformis cerebri, s. major) arises from the centre of the upper face of the dura-mater, under the form of a prolongation which descends vertically between the two hemispheres of the cerebrum in all their length. It gradually increases in height from before backward. Posteriorly it rests by its lower edge on the tentorium, of which it forms a part, and its anterior portion which is much more extensive,, terminates in a loose and concave edge. It advances above the centre of the corpus callosum, but does not touch it except at its posterior extremity, for the arteries of the corpus callosum are at least one line distant from it.
The large falx is attached by its external edge forward to the internal frontal crest, and in the rest of its extent to the inside of the sagittal suture. The upper longitudinal sinus is situated between the two layers which form its external edge superiorly. It is also divided at its concave edge into two layers which receive between them the inferior longitudinal sinus and the right sinus. The posterior part of its inferior edge is continuous on each side with the tentorium.
This prolongation is smooth on its two faces. It has manifestly a fibrous structure.
Most of the fibres which form it are oblique from behind forward and from below upward. They are more horizontal the more anterior they become. Others, which are much fewer, and which cross the preceding, are observed particularly at the anterior part and at the upper edge of the falx, so that we cannot there mistake the analogy between the dorsal and ventral faces any more than the distinctive character of these two faces, which is that the first is stronger than the second.
The falx presents not very unfrequently, especially near its lower edge, considerable spaces, openings through which the internal walls of the two cerebral hemispheres touch and sometimes even adhere together.
2d. The cerebral dura-mater has not the same relation as the spinal in regard to the nerves which emerge from the skull ; it generally accompanies them farther than this latter and follows the spinal nerves so that, for instance, the commencement of the three branches of the trifacial nerve is inclosed in special canals. The envelop it gives unites them still more closely, and when they emerge from the skull it is continuous with the periosteum of the bones, while the spinal duramater terminates only in the cellular sheath of the nerves.
III. LIGAMENTUM DENTICULATUM.
§ 1801. The spinal marrow has one mode of attachment which the cerebrum has not, and which very probably serves to compensate for the liberty which it enjoys in the vertebral canal, on account of the disproportion between its volume and the caliber of this canal. We mean the ligamentum denticulalum, or serratum.
This ligament descends on both sides between the anterior and the posterior series of the roots of the spinal nerves, commences directly above the occipital foramen and terminates some distance above the extremity of the spinal marrow, at the summit of its inferior expansion. It is situated above the vertebral artery when it enters the skull, and before the accessory nerve : in the rest of its course it is nearer the anterior than the posterior roots. It is smooth, thin, narrow, whitish, and composed of a series of triangular slips united at their base by a very thin band. The base of these slips is thin and flat, and rests directly on the pia-mater. Their summits are rounded, harder, thicker, and turned downward, and are attached to the arachnoid membrane and still more firmly to the dura-mater. There is generally one between each pair of cervical and dorsal nerves, and they are usually nearer the lower than the upper nerve. Hence, in most subjects, there are twenty of them. Their number, however, is by no means constant : they are frequently fewer than the nerves, because one slip between one or several pairs of nerves is generally deficient, although there is nothing determinate in this respect. More rarely two are found between two pairs of nerves. Their whole number then varies from twelve or fourteen(l) to twenty-two. or twenty-three. (2) The ligamentum denticulatum enlarges from above downward, and the slips separate still more from each other the lower they are. Below these latter we observe a fold about an inch in length which proceeds along the sides of the spinal marrow, but rarely or even never descends to the real termination of this cord. Not unfrequently also the ligamentum denticulatum is perforated, especially at its upper part, whence it has a reticulated appearance. (3)
Judging from its texture, this ligament seems to belong to the class of fibrous organs, since not only the slips but also the external part of the membrane extended between them have a silvery lustre, and longitudinal fibres are very evident internally. It also adheres very intimately to the spinal dura-mater, while it is attached to the piamater only by a cellular tissue which is in fact solid, but is easily torn. We cannot then consider it as a prolongation of the pia-mater as do many anatomists, whose opinion Bichat has justly opposed, (4) and it is more proper to regard it as an internal prolongation of the dura-mater, since the cerebral portion of this membrane sends those prolongations which are so remarkable between the different regions of the mass of the encephalon.
(1) Sabatier, loc. cit. p. 460.
(2) Gordon, loc. cit., p. 190.
(3) Vicq-d’Azyr, loc. cit., p. 603.
(4) Anat. gêner . vol. iii. p. 122.
Chapter IV. Periodical Differences of the Central Portion of the Nervous System During its Development
§ 1802. The development of the central part of the nervous system^) has been studied but a few years : hitherto only the general traits of this history, its most prominent features, have attracted attention.
I. SUBSTANCE.
§ 1803. The principal differences in the substance of the central part of the nervous system relate to the extent, form, situation, texture, color, and relations with the envelops.
1st. Extent. The central part of the nervous system is generally much larger in proportion to the body the younger the organism is. The spinal marrow occupies all the length of the vertebral canal until the end of the third month of pregnancy. It is true that from this period it begins to shorten, but it is not confined to its normal limits till the eighth month of pregnancy. It is also thicker during the early periods of life.
The encephalon, with the exception of the cerebellum, is also proportionally much more extensive. It must not however be thought, especially in regard to this viscus, that a greater extent is perfectly synonymous with a greater mass, for the parietes are proportionally much thinner than at a more advanced age.
The encephalon until perfectly developed, continues to be larger in proportion to the body than it is finally : for between six and seven years, according to Wenzel, (2) and Soemmerring(3) states even from the third year, it has acquired the size and weight which it will retain through life.
2d. Situation. The very imperfect development of the posterior part of the vertebral column causes the spinal marrow and the encephalon to be much looser and less attached during the early periods of existence.
(1) Tiedemann, Anatomie du cerveau , contenant l'histoire de son développement dans le fœtus , trans. by Jourdan, Paris, 1823. — Schoenlein, Von der Hirnmetamorphose, Wurzburg, 1816. — Serres, Anatomie comparée du cerveau dans les quatre classes de vertébrés, Paris, 1824. — Desmoulins, Exposition succincte du développement et des fonctions du système cérébro-spinal ; in the Archives générales de médecine, juin 1823. — Rolando, in several articles of the Dizzionario periodica di medicina, Turin, 1822 et suiv.
(2) De penitiori struct, cereb., p. 266.
(3) Tab. baseos encephali, p. 13.
3d. Form. The differences in respect to the form are very remarkable.
I. SPINAL MARROW.
а. The caliber of the spinal marrow is much more uniform the younger the fetus is. The prominences which correspond to the nerves of the extremities develop themselves only in proportion as the extremities appear.
б. The spinal marrow which is entirely full and solid, not only in full grown subjects but already even during the early months of existence, incloses at first in all its length a canal which is uninterruptedly continuous with the cerebral fissure, and which is larger in those parts where the spinal canal is prominent.
This canal is at first not rounded, but oblong from before backward, and if we except a small plate which bounds it anteriorly, it extends through the whole thickness of the spinal marrow. Hence the internal face of the latter is at first continuous with the external, as the whole canal is much larger during the early periods of life than at a more advanced epoch, and then it does not resemble a proper canal so much as a fissure, which separates almost entirely the two lateral portions of the spinal cord. This canal also gradually closes and contracts from without inward at the posterior part : the spinal marrow then folds longitudinally forward and backward : hence arise anterior and posterior longitudinal grooves, which never communicate with the central canal, even as the cerebrum and the summit of the spinal cord, present, during life, not only two longitudinal grooves, an upper and a lower, but also two central cavities separated from these same grooves by medullary substance in at least most of their extent, and by the piamater in all their course. The longitudinal grooves of the pia-mater, however, are broader during the early periods of existence, and the posterior not unfrequently entirely disappear as the subject grows older.
c. Although the spinal prolongation is at first much larger in proportion to the whole body than it is in the adult, we soon see an opposite relation between it and the encephalon, both from the development of the latter, and from the diminution of the spinal cord.
Thus we have found that the proportion between the spinal marrow and the cerebrum was still as 1 : 107, and even as 1:112, in the full grown fetus and the child of five months : for the cerebrum of the fetus weighs nine ounces and four drachms, and that of the child five months old, twenty-one ounces, the spinal marrow of the former two scruples and five grains, and that of the second a drachm and a half. In a fetus of five months, on the contrary, the proportion was as 1 : 63, since the cerebrum weighed six drachms, one scruple, and eight grains, and the spinal marrow six grains. It was as 1 : 18 in a fetus of three months, where the brain weighed thirty-six grains and the spinal marrow two. In the adult it is as 1 :40. These estimates will serve to rectify the calculations given by some anatomists, of the differences observed at different periods of life, in the respective proportion of the encephalon and the spinal cord.(l)
The younger the fetus, the larger the spinal marrow in proportion to the encephalon. It is evidently larger and heavier in proportion to this latter, even in the human fetus of three months, than in the adult, either on account of its greater size, or of the smallness of the encephalon ; but the latter soon exceeds it more than in the adult, both because it increases much, and because the spinal cord itself diminishes.
II. MEDULLA OBLONGATA.
a. The medulla oblongata, except perhaps in the earliest periods of its formation, is much more distinct from the spinal marrow, and the angle between the two organs is much nearer a right angle, the younger the fetus is.
b. It is also proportionally much more developed during the early periods of life than at a more advanced age. This proposition is applicable particularly to its lower and anterior part, which concurs to form the cerebrum. Hence, why the medulla oblongata is still more distinct from the spinal marrow in the full grown fetus and the young child than in the adult, and why, also, all its parts, particularly the eminences of its lower face, the pyramids and olivary bodies, are then more permanent, and separated by more distinct limits. This circumstance seems to be in direct ratio with the greater development of the cerebrum.
c. The calamus scriptorius is much larger in the early periods of existence, because its parietes are then thinner, and the distance between them from behind forward is greater. The transverse cord which closes it superiorly, does not exist at first, but it is greater during the early periods of fetal existence than in the adult.
(1) Carus ( Anatomie und Physiologie der Nervensystems, p. 262) expresses himself upon this subject very vaguely, for he merely states that the proportional volume of the spinal marrow and cerebrum, is that which varies the least in the human fetus and the adult, both because the disproportion between the encephalon and the spinal marrow seems less from the great volume of this latter, and because the type of the human species always predominates even here. He, however, admits farther on (p. 266), that the spinal marrow is always larger, compared with the encephalon in the human fetus than in the adult, although it. is not much larger than when the subject is fully developed. Tiedemann (loc. cit., p. 141, 142, 143) makes a more exact statement : he says that the volume of the spinal marrow is much larger compared to that of the brain the younger the fetus is; that the human fetus perfectly corresponds to animals in this respect, and that the cerebrum becomes much larger in proportion to the spinal marrow the nearer it is to its period of perfect development. From what we have said above, it follows that this proposition is true, at most only for the early periods of fetal life ; that an inverse proportion soon supervenes, and that consequently, we observe, before that which marks the perfect state, another’ where the encephalon presents, in proportion to the spinal marrow, a much greater volume than it has in the adult, so that regarding only the mass and weight, we find at this period a relation more favorable to the cerebrum than that observed in full grown subjects.
The 'white striæ upon the floor of the calamus scriptorius , do not appear till some months after birth, while the gray eminences before them are visible in the fetus of three months.(l)
d. The olivary bodies appear in the third month of fetal existence, (2) but when the fetus is full grown, they are formed externally only of gray substance. In the third, and even in the fifth month of pregnancy, we discover within them a small cavity, which disappears entirely at the sixth.(3) When they have become completely solid, the gray substance ramifies there at first more simply than it does afterward.^)
e. The pyramids appear much sooner than the olivary bodies, and are also, proportionally speaking, much larger at first than in the adult.
f. The corpus callosum does not appear till late and till the third month. It is at first thinner and shorter. Its size in proportion to that of the medulla oblongata is still less. The longitudinal groove of the lower face is deeper in the full grown fetus than in the adult.
HI. CEREBELLUM.
The cerebellum is one of the parts of the central mass of the nervous system which are developed the latest.
It appears during the sixth week of fetal existence as a very small layer, at first hardly visible, thin, horizontal, situated transversely on and before the calamus scriptorius , divided by a deep median fissure into two halves, which is only a slight appendage of the tubercula quadrigemina, with which it is continuous upward and forward at an obtuse angle. The transition is made afterward less insensibly, because the anterior valve is developed between the two organs. Very probably, the part of the cerebellum which exists first, is only the valvule of Vieussens, which opinion is supported by this thinness, and the fact that the cerebrum, generally considered, is formed from below upward. This primitive layer gradually becomes thicker from above downward, and finally gives rise to the cerebellum : but it is very low in regard to its other two dimensions, and is very small in proportion to the other parts of the encephalon.
In the full grown fetus, the relation of the cerebellum to the cerebrum, is still generally as 1 : 23, since the cerebrum weighs between nine and ten ounces, and the cerebellum about three and a half drachms. The cerebellum, however, rapidly attains its normal proportional size.
(1) Wenzel, Depen. struct, cereb., p. 320, 321.
(2) Carus, loc. cit., p. 289. — Tiedemann asserts that they are not developed till the end of the fifth or the beginning of the seventh month.
(3) Carus, loc. cit., p. 289.
(4) Carus, loc. cit., p. 290.
We have determined that the relation one month after birth is as 1:17, and five or six months later is as 1 : 8, at which period the cerebrum weighs about sixteen ounces, and the cerebellum two.
The component parts of the cerebellum, however, are developed earlier than those of the cerebrum. We observe grooves on its surface about the end of the fourth month of pregnancy : they appear first at its central part. The largest also, those which divide the organs into lobes, appear before the small, and the latter are at first much more superficial and more simple than at subsequent periods.
The rhomboid body of the cerebellum includes at first a cavity, which still appears at the third month.(l)
JV. CEREBRUM.
If we except the early periods when the spinal marrow and medulla oblongata predominate so manifestly, the cerebrum is at first much larger and heavier in proportion to all the other parts of the centre of the nervous system than in the adult.
The great differences in its structure, oblige us to consider its parts in the same order as when we described them.
a. Cerebral prolongations. The most remarkable thing in regard to the cerebral peduncles, is the direction they assume at first : their posterior part rises perpendicularly, and is continuous at an acute angle with the anterior, which also descends as vertically as the other, and directly before it.
They are besides much larger in the fetus than in the adult, in proportion to the other parts of the cerebrum.
b. Tubercula quadrigemina. These tubercles, with the cerebral peduncles, are at first the largest part of the cerebrum. They are then much larger in proportion to the volume they have afterward, than one of the central portions, and form the highest part of the cerebrum, so that they have sometimes been mistaken for the cerebellum. (2)
They do not at first deserve the name which is generally given to them, for they are separated neither lengthwise nor breadthwise, but form a very elongated homogeneous mass. Their lateral halves are probably not united at first on the median line by nervous substance, and the communication between them is established only by the piamater.
Their longitudinal groove appears a little before the transverse. It is developed from before backward, so that it separates the two anterior eminences sooner than the two posterior. The transverse groove is situated at first, proportionally speaking, farther back, whence the anterior pair of eminences is always much larger proportionally at first than in the adult.
(1) Carus, lac. cit. s p. 285.
(2) Harvey, De generat. Amsterdam, 1662, p. 301.— Autenrieth, Suppl, ad hist, emb., p. 21.
The tubercula quadrigemina are still larger in proportion to their breadth, in the fetus than in the adult. Although in the latter they are more long than broad, they however possess their normal length at the period of birth, and after this time they only increase more or less in breadth.
Their parietes are much thinner if examined at a period still nearer conception. They also inclose a considerable cavity which gradually becomes smaller as their parietes thicken, and which is united by the small grooves within them.
c. Pineal gland. It would seem as if this body did not begin to appear till the third or fourth month of pregnancy.(l) It is at first more rounded and flat. We find no trace of concretions until the period of birth, but sooner or later, sometimes not till the seventh year, a soft and viscous substance forms before it, which is situated on the posterior commissure, and gradually hardens after the age of seven years, and begins by surrounding it. Sometimes, however, we find no trace of pineal concretions in much older subjects, a rare peculiarity which is established by the observations of Wenzel and ourselves. The number of these concretions generally increases in age. In youth, the viscous substance and the concretions are situated before the pineal gland : in the adult we find them also in the anterior depression and in the substance of the gland: in old subjects they exist in all these places at once. These concretions are paler in infancy and in old age, than in the intermediate periods. (2)
d. Optic beds. These eminences are larger in the fetus than in the adult, in proportion to the corpora striata and the hemispheres.
At first they are entirely separated from each other. Afterward, but always at an early period of conception, they adhere on the limits of their upper and internal faces, by a thin but very distinct medullary layer, which extends between them like a bridge. Much later, and about the fourth month, the commissura mollis is formed, but it is at first much larger than in the adult, which character it still preserves in the full grown fetus, and even in infancy. The upper bridge has long disappeared at birth.
e. Corpora striata. These bodies appear later than the optic beds, They are at first smaller in proportion to the latter and the hemispheres, and are developed in the form of prominences of the inferior wall of these latter ; they are never hollow internally, and are much more distinct from the hemispheres and the optic beds as the fetus is younger.
f. Hemispheres. We have always found the hemispheres of the cerebrum before the corpora striata. They are much larger and more extensive in proportion to these latter, the younger the fetus is. At first, however, they are extremely small in proportion to the other parts before which they are situated, but do not extend beyond them
(1) Tiedemann, loc. cit., p. 216.
(2) Wenzel, loc. cit., p. 315.
on the side. At first they are very rounded, and then become more
oblong than they are when fully developed. We are not yet certain
whether they are separated from each other at the period of then formation, or if they form only one rounded transverse prominence. Observations upon the fetuses of sheep, analogy with the development of
other parts, the tubercula quadrigemina for instance, and the manner
in which they are developed in the animal series, render the second
hypothesis probable. (1) This period, however, if it occurs, (of which
we have not the least doubt, from researches made recently upon very
young fetuses of sheep,) passes very quickly, and is replaced by another
which presents an arrangement opposite to that we have mentioned.
The two hemispheres separate from each other completely ; their internal parietes are perfect except a email epace n t their posterior part,
and their internal faces are, it is true, placed one against the other ;
but we can separate them entirely without the least laceration, as in
the cerebral hemispheres of birds.
The hemispheres continue to increase and gradually extend outward, backward, and upward, so that they cover first the optic beds, then also the tubercula quadrigemina, and finally the cerebellum.
Their surface continues smooth for a long time, and we observe there no trace either of the division into lobes, or of circumvolutions and anfractuosities. Their parietes are at first exceedingly thin in proportion to the space they circumscribe.
The fissure of Sylvius is developed at the third month, under the form of an oblique fissure, between the anterior lobe and the middle lobe ; but it continues for a long time more superficial than in the adult, and forms at first only a slight depression, which depends particularly on the fact that the middle lobe is then proportionally much shorter, and only increases gradually from above downward. Hence, why the isle of the fissure of Sylvius is at first entirely loose and unattached. The circumvolutions and the anfractuosities appear afterward, not until the fourth and fifth month, and the internal of the upper face appear before all the others. The prominences of the isle of the fissure of Sylvius form last, and we have found no trace of them in the fetus of eight months.
g. Those parts of the cerebrum which serve to unite the others, the corpus callosum and the fornix, are developed the last. At first we find in their place only a fold of the internal wall of the hemispheres, which is entirely hollowed outward, and which projects within the cerebral cavity. This fold gradually disappears in its anterior part, and as it vanishes, the corpus callosum forms from before backward, so that this latter seems to depend on the circumstance that the cerebral substance turned at first outward, is reflected inward, and the internal walls of the two hemispheres then unite in this latter direction.
(1) Meckel, Deutsches Archiv fur die Physiologie, vol. i. p- 385.
But below this point the internal parietes separate still more, ami
thus form the ventricle of the septum, which finally contracts com
siderably.
The fornix and the corpus fimbriatum arise from the enlargement of a small cavity in the hemisphere through which the pia-mater penetrates from before backward to produce the large cerebral fissure which increases its distance from the optic bed.
The mammillary eminences form until the seventh month a single eminence, which perhaps develops itself in the same proportion as the internal wall of the lateral ventricles is separated by the pia-mater which penetrates within it.
The anterior commissure appears at three months.
The ventricles of iko cerebrum present several remarkable differences at different periods of development.
It is a general law, that they are larger in proportion to their parietes, the younger the organism is. This circumstance depends principally on the thinness of their parietes, as we have already stated when speaking of the tubercula quadrigemina, the optic beds, the cerebral hemispheres, and the medulla oblongata. The fossa of the medulla oblongata is also much larger in the early periods from the great development of this part.
The form of the hemispheres also varies at different periods of life.
In the early stages of pregnancy, the hemispheres form in fact only one large cavity, since there is then no ventricle of the septum nor corpus callosum, the space between the internal walls of the hemipheres is in no manner closed.
At a later period the ventricle of the septum, which when the subject is perfectly developed is generally entirely separate from the others, communicates with the third ventricle below the anterior commissure.
The third ventricle is not at first divided into an upper and a lower canal by the commissura mollis ; but in the latter periods of fetal existence this separation is more marked than in the adult.
The lateral ventricles are not divided at first into three horns, but are entirely single. The anterior and middle horns are developed the first when the corpus striatum forms. The posterior horn is the last to appear. The formation of the latter and this complete separation of the first two, depend on the thickening of the parietes of the hemispheres, and the increase in the size of the corpora striata.
4th. Texture , consistence , and color. The nervous system in general and particularly its central mass, are extremely soft in the early periods of life. It is curious however, that notwithstanding this softness, its fibrous texture(l) is easily distinguished, and is even more evident than in tire adult, even as in fishes we observe it in several parts of the cerebrum without recurring to any artificial means to render it more evident. The fibres seem to be arranged in elongated and pyramidal fasciculi, the summits of which are turned inward, and the bases of which look towards the surface of the cerebrum ; at least we have observed this phenomenon several times in the brains of fetuses macerated for a short time before or after then immersion in alcohol.
(1) Petsclie, iS i/tlog. obs. anal. select. Halle, 1736, p. 33, § 76.
The difference between the gray and the white substance is visible
at a later period. It appears earlier in the spinal marrow than in the
cerebrum, where it is evidently formed from behind forward, and from
below upward. It is already very evident at seven months in the
spinal marrow, and perhaps even it is observed there sooner. The
gray substance has then even a deeper tint than that which marks it
afterward. But the medulla oblongata is still entirely gray towards
the period when the embryo is fully grown. After this period we first
'see the pyramids whiten, then the olivary bodies are covered with
white substance. The annular protuberance is still entirely gray externally in the first weeks after birth, although the longitudinal fibres,
extended into the pyramids, which pass through it, are entirely white.
The transverse fibres soon afterward also become white : the inferior and
external before the superior and internal, which at two months are but
few in number, and scarcely perceptible. The difference between the
gray substance and the white substance is observed in the cerebellum
during the later periods of fetal existence. The gray substance however
is much greater there in proportion than in the adult. The yellow
substance, situated between the gray and the white, rarely forms
before the end of the first year, and it never appears in the course of
the first six months.
The cerebral peduncles are still gray externally in the first periods of life, although the prolongations of the pyramids within them have already a whitish color at this time. Some months after they are often entirely white on the surface. Sometimes however we have found them entirely gray in children five months old, while the white substance was completely developed in the medulla oblongata and the cerebrum. It is true they had then a brighter tint than the rest of the white substance. The black substance which is met with internally in the adult, is simply gray in the first year. The mammillary eminences are usually entirely gray at five or six months.
The difference between the gray and the white substance already begins to show itself in the other parts of the cerebrum at the period of birth, or at least in the first few weeks of life. Their arrangement, however, then differs much from what it is afterward. The optic beds and the corpora striata are entirely gray, although having very manifestly a fibrous texture, or at least it is very difficult to distinguish the two substances, because the gray is but slightly colored, and the white is grayish. On the surface of the corpora striata is a very vascular layer, giving them a redder and a deeper tint than belongs to them, and under this is a homogenous mass of a brighter color and still entirely gray. There are developed in this layer yellowish white rays which perfectly fit with it, are still less abundant than it, and are not attached to those of the cerebral peduncle : but we have not yet determined with certainty at what period they appear, although they are evidently formed in the first weeks after birth and not in the latter of fetal existence. These yellow rays disappear in the course of the first month. At the same time the red and vascular substance is discolored, and a medullary band scarcely about a line broad, forms between it and the external gray substance, and gradually extends particularly inward.
This layer formed alternately of red substance and of a yellowish white substance about six lines broad, presents a very marked analogy with the fimbriated nucleus of the olivary bodies and of the cerebellum. But the cerebrum differs from the cerebellum and the medulla oblongata, inasmuch as its corpus dentatum is only a temporary formation, while in the other two it is permanent.
The gray cortical substance is much thicker in the cerebrum in the early periods of life than subsequently. At five months its average measure of thickness is about two lines.
As the intermediate yellow substance is not developed in the cerebellum at this period, so too the envelop of the posterior circumvolutions of the cerebrum is not yet divided by an intermediate medullary band into an external and an internal layer ; we must then attribute the absence of this arrangement to a suspension of development which is sometimes observed in adults.
V. ENVELOPS.
§ 1804. The pia-mater is generally much more vascular and much better developed, but also united much less intimately with the nervous substance the younger the fetus is. The internal pia-mater seems to form gradually. The choroid plexuses seem to participate remarkably in this difference dependent on age ; but they do not exist at all during the earty periods, although the cavities which include them are already formed, so that the differences in their development depend according to all appearances less on the increase of the mass of the cerebrum than on the extent of its cavities, and they are in direct ratio with the activity of the secretion even as in the mammalia, where the ventricles are larger than those of man in proportion to the medullary mass, the choroid plexuses are also m uch more developed than in the human species.
The arachnoid membrane , if we except perhaps the first periods, is at first much more evidently distinct from the pia-mater and from the dura-mater in all its extent. It is also proportionally softer, thicker, and less transparent. We find between it and the other two membranes, and also in the cavities of the encephalon and the spinal marrow, during the early periods of life, much more fluid than exists afterwards. Its differences at different periods of its development are then most probably in direct ratio with its power of secretion, since when the latter is increased by a morbid state the membrane is changed exactly in the same manner. It generally becomes less pellucid, thicker, and harder, as the subject grows older.
The glands of Pacchioni are not generally observed till at an advanced period of life.
The dura-mater is proportionally more vascular, but thinner and less distinctly fibrous in the early stages of life than at a more advanced period. Its prolongations, particularly the perpendicular, are very thin, much less extensive, and easy to divide into two lateral layers in all their extent, so that considered generally they are but slightly developed. The connections between the skull and the cerebral duramater which is still imperfect, are much more intimate in the fetus than in the adult. The substance between the spinal dura-mater and the vertebral column is at first much more abundant, but also thinner and gelatinous : it does not become changed into fat until after the first year of birth.
§ 1805. Notwithstanding all the researches hitherto made, the mode of the formation of the centre of the nervous system is not yet ascertained. Two of the characters presented by it at all periods of life are very much developed in the early states, viz. the ventricles and the two lateral corresponding halves. We may then conjecture that the central portion of the nervous system forms in the centre of a fluid and down it, that it there assumes the form of a hollow canal, or that it is developed there in layers or cords more or less separated on the median line, which gradually unite to form a cavity. In this latter hypothesis, the number of degrees of development through which the cerebrum and spinal marrow pass would be greater than in the first, which does not admit of the primitive simple form of layers. But there are facts which favor the latter opinion, and although it renders the formation of the central mass of the nervous system more complex, we must not discard it to admire wrongly the simplicity of nature in her operations. The facts we allude to are the almost entire division of the spinal marrow into two lateral portions, which is seen from the first, the possibility of entirely separating also the anterior cords from each other, and thus of changing the spinal cord into two lateral cords : the great breadth and the slight thickness of the medulla oblongata ; finally the total separation of the two lateral halves of the cerebellum, probably also of the tubercula quadrigemina, and very certainly of the optic beds. Thus the central mass of the nervous system is developed from below upward, although we are as yet unable to determine if it is by one or two layers : these layers cross from before backward, curve inward to meet each other and blend on the median line, giving rise in this manner, first to a semi-canal and then to a perfect canal. This theory is supported not only by the facts supplied by the history of the fetus, but also by the development of the nervous system in the animal kingdom. The dorsal medulla and the cerebrum of worms and insects evidently correspond to the inferior or anterior cords of these same parts in the upper classes of animals, and we may without much trouble extend a higher degree of organization to these organs partly by supposing the superior cords to be added, and partly by supposing them united posteriorly, bj r which the layers or cords which first existed assume the form of a canal.
The final development of the central part of the nervous system is by the increase of the mass, which augments the thickness of the parietes of the ventricles, and contracts the latter. Next supervenes a period when the mass settles, so that the surface which was at first smooth and united becomes very uneven, and at the same time much more extensive. Différences then occur in the nervous substance which divides into gray and white, by which phenomenon the development of its intimate structure terminates. These different characters generally appear in the parts in the same order as they are formed. The spinal marrow is first perfected in every respect. The tubercula quadrigemina change but slightly after birth. The cerebellum seems to be an exception to the rule, for although it is formed late, it becomes perfect in respect to form and texture long before the cerebrum, and even before the annular protuberance.
Chapter V. Of the Motions of the Central Mass of the Nervous System
§ 1806. The central mass of the nervous system has certainly two motions(l) which are very evident in the brain. One depends on the pulsation of the arteries, the other on respiration ; of these, the latter is much less frequent than the former. Both consist in an alternate rising and falling of the encephalon, which in the second is undoubtedly enlarged and contracted alternately. Respiration determines the second kind of motion, because when the air is expelled from the lungs it is more difficult for the blood to return to the brain, while on the contrary, its return is more easy during inspiration. The encephalon enlarges then in the first of these two cases, and collapses in the second.
m Schlichting 1 , De motu cerebri ; in the Mem. prés ., vol. i. p. 113. — Lorry, Sur les mouvemens de cerveau, cl de la dure-mère , same journal, vol. iii. mem. i, p. 277, mem. ii. p. 344. — Haller, Experim. ad motum cerebri a rcfiuxu sanguinis natum ; in the Ôpusc.phys., vol. i. p. 231.— Lamure, Sur la cause des mouvemens du cerveau ; in the Mém. de Paris, 1753 —Richard, in the Journ.de méd., vol. xxix. 1768, p. 140. — Ravina, De motu cerebri ; in the Mem. de Turin, 1811. — Portai, Mém.. sur un mouvement qu’on peut observer dans la moelle épin ière ; in the Mem. sur plus, malad., vol. ii. p. 81. — Magendie, Sur un mouvement de la moelle épinière isochrone à la respiration ; in the Journ. de phys. e.rpér., vol. i. p. 200.
Chapter VI. of the Central Portion of the Nervous System in the Abnormal State
(1)
§ 1807. Most of the deviations in the formation of the central part
of the nervous system are congenital. They all relate to the existence ,
the number , the situation , the size , and the form of this mass.
§ 1808. Existence and number. (2) Not unfrequently a greater or less portion of the central mass of the nervous system is deficient by a primitive deviation of formation. In ctceplialia vera( 3) the spinal marrow is usually developed as far as the vertebral column extends, and in this place terminates in a point, where it divides like the cerebrum into two rounded eminences. The cerebrum is then entirely deficient, or at least exists but very imperfectly, except when there is a rudiment of a head in spina bifida and in acephalia falsa , which is similar to spina bifida and which frequently coexists with it. The cerebrum
(1) J. Baader, Obs. mcd. incisionibus cadaverum anatom icis illustrate, Friburg, 1762. — J. F. Meckel, Rich. anat. physiol, sur les causes de la folie ; in the Mém. de Berlin , 1764. — J. E. Greding, Melancholico-maniacorum et epileplicorum quorumdam in ptochotropheo Waldhemiensi defunctorum sectiones ; in Ludwig, Adners, med. pr., Leipsic, 1771, vol. ii.-iii. — Burdach, Beytrage zur nähern Kenntniss des Gehirns in Hinsicht auf Physiologie, Med. und Chirurgie, Leipsic, 1806. — Home,
Observations on the functions of the brain; in the Phil, trans., 1814, voL ii.
Lallemand, Observations pathologiques propres à éclairer quelques points de physiologie, Paris, 1818. — J. Abercrombie, lieber die Krankheiten des Gehirns und des Rückenmarks ; with additions, Nasse, Bonn, 1820. — Id., Observations sur l'inflammation chronique du cerveau ; in the Journ. compl. des sc. méd., vol. i. p. 346. — Lallemand, Recherches anatomico-pathologiques sur l'encéphale et ses dépendances Paris, 1820 et suiv. — Georget, De la folie, considerations sur cette maladie, suivies de recherches cadavériques, Paris, 1820. — GeofiFroy-Saint-Hilaire, Philos, anat., monstruosités humaines, Paris, 1823. — Serres, Rccherch. sur les malad, organiques du eervelet ; in the Journ. dephys. cxp., vol. ii. p. 172, 249, vol. iii. p. 114. — C. Oppert, Diss. de vitiis nervorum organicis, Berlin, 1815. — Magendie, Hist, d'une maladie singulière du système nerveux ; in the Journ. de phys. exper., vol. ii. p. 99. — A. L. J„ Bayle, Mémoire sur quelques points de la physiologie et de la pathologie du système nerveux ; in the Revue médicale, vol. i. p. 46.— L. Martinet, Observations tendantes à éclairer la doctrine des phénomènes spasmodiques dans les cas de ramollissement du cerveau ; same journal, vol. i. p. 56. — A. L. J. Bayle, Mémoire sur l’existence de la paralysie du même côté que la lésion cerebrale qui la determine ; same journal, vol. i. p. 33.
(2) The following terms have been proposed for the deviations in the formation of
the central mass of the nervous system which may appertain to this class: aneuria, the deficiency of the whole nervous system : amyelencephalia, simultaneous absence of the encephalon and spinal marrow : amyelia, entire absence of the spinal marrow ; atelomyclia, imperfection of the spinal marrow; ancncephalia, absence of the encephalon. F. T.
(3) The most complete treatise on acephalia, is that of Tiedemann, Anatomie der hopflosen Missgeburten, Heidelberg, 1813. — See also Tiedemann, Beobachtungen über Missbildungen des Gehirns und seiner Nerven ; in the Zeitschrift fur Physiologie, part i. 1824, p. 55.
496
DESCRIPTIVE ANATOMY.
and the spinal marrow arè frequently partly or wholly deficient, although no mark leads us to suspect that they have existed anteriorly.
When the facial portion of the skull is imperfectly developed, the anterior part of the encephalon is also deficient, or at least is very imperfectly formed. The anomaly generally extends only to the cerebrum : the medulla oblongata is rounded before, especially when there is no trace of the cerebrum, or when the latter is replaced by a thin vesicle, although we cannot trace the hemispheres, the corpora striata or the optic beds.
More rarely only some parts of the spinal marrow and encephalon are deficient, while these two organs and the whole body are otherwise perfectly developed. (1) The commissures are most frequently deficient, a very curious phenomenon as these parts are formed latest in the animal series and in the fetus. The commissura mollis of the optic beds is most often absent ;(2) but this is developed latest in the embryo, and birds are destitute of it. The corpus callosum is more rarely wanting, (3) and the annular protuberance still more rarely in subjects where the cerebrum and the cerebellum are regularly developed in all other parts. We know of no instance of the want of an anterior and posterior commissure, which is completely formed in the fetus and in the animal series before the parts of union above mentioned.
Authors frequently mention the absence of the pineal gland and its concretions ; but the pretended deficiency of this gland depends doubtless upon a careless or too hurried dissection.
The imperfect development of inequalities on the external and internal surface of the cerebrum, is connected with the total absence of parts which possess a great character of individuality. Malacarne states that the intellectual faculties are developed directly in proportion to the number of the layers of the cerebellum, which vary from six hundred to eight hundred. (4) So too the external surface of the cerebrum is sometimes more or less smooth, a circumstance which perhaps is also connected with the degree of intelligence, for of all parts of the encephalon the circumvolutions vary the most. (5) In regard to the internal eminences, the prominence of the posterior horn of the lateral ventricle is deficient more frequently than that of the middle horn. The imperfect development of the external circumvolutions is not un (1) Breschct has observed in an idiot three years and a half old, an imperfect development of the outer part of the left hemisphere, the corpus striatum, and the optic bed of the same side, ( Note sur des enfans nouveau nés, chez lesquels V encéphale offrait un développement imparfait ; in the Journ. dephys. exp., vol. iii. p. 232.)
(2) We have reported previously several instances. Grcding (lue. cit., vol. iii. p. 650) observed, that of the great number of brains he has dissected, the commissura mollis of the optic beds was deficient in seven only.
(3) Reil, Archiv. fur die Physiologie, xo\. xi. p 341. — Meckel, Handbuch der pathologischen Anatomie, vol. i. p. 301. — Wenzel, De penit. structura cereb., p. 302.
(4) Neuro-Encefalotomia, Pavia, 1791.
(5) Wenzel, chap. iii.
U* IHE JNEKVOUS SYSTEM.
497
frequently attended with an analogous arrangement of the internal
eminences : but perhaps it is not so correct to admit the relation of
cause and effect between these two states, for instance to attribute the
second to the first,(l) as to ascribe the origin of both to the same cause.
The deviations in formation by excess are much less common than those by defect, particularly when the body is single, and they at most affect only insignificant parts. Here we may mention among others the existence of a small prolongation of the decussation of the optic nerves which goes forward, (2) and is perhaps only a repetition of the hypophysis, the increase of the number of the internal and external prominences which is little less frequent, the doubling of the commissural mollis of the optic beds, finally the existence of a double pineal gland, (3) although this anomaly depends perhaps on the division of the pineal gland, which is generally single.
2d. Situation. The anomalies in respect to situation generally de* pend on the imperfect manner in which the organs which surround the spinal marrow and the encephalon are developed in spina bifida and in acephalia falsa , whence they are left more or less exposed.
In encephalocele ( hernia cerebri) a greater or less portion of the encephalon projects outward, and is or is not covered by the common integuments. (4) This hernia which generally supervenes after a congestion of serum within the encephalon or the skull, usually occurs either through one of the points of the osseous envelop which always continue open, as the occipital foramen, or through one of those spaces which are gradually filled up, as the fontanelles.
We have as yet no well authenticated instance of anomalies in the respective situation of the parts of the encephalon.
3d. Volume. Excess and deficiency in volume are not rare phenomena in the central part of the nervous system. Both may be primitive and congenital, or consecutive and accidental.
a. Smallness. The spinal marrow is rarely too small from a primitive deviation of formation ; and it sometimes diminishes in tabes dorsalis. (5)
(1) Gredins', loc. cit., vol. iii. p. 613.
(2) Wenzel, p. 147.
(3) Sœmmerring-, in Noethigy Dc decussatione nervorum, opticorum, Mayence, 1786.
(4) Meckel, Handbuch der pathologischen An., vol. i. — Neagele, Sur Vencephalocele ; in the Journ. compl. des sc. med., vol. xiii. p. 207.
(5) The wasting of the spinal marrow has been observed by Bonet ( Sepulchretum , voi. i. p. 305, 370). Morgagni has often remarked that the spinal marrow in persons affected for a long time with hemiplegia, was considerably diminished in all the lateral portion corresponding to the side affected. ( De sed. et caus., ep. xi. sect. 60). This wasting has been observed also by Salzmann, Chaussier, Olivier. It seems to be generally attendant on old age, and may supervene whenever there is a slow and long continued compression of the spinal prolongation, as in the disease of Pott. We have even known in some cases of this kind, the medulla to disappear entirely at the part compressed. Olivier mentions a remarkable instance of it (loc. cit., p. 143).
Vol. II.
63
498
DESCRIPTIVE ANATOM!',
The encephalon presents instances of this deviation of formation much
more frequently at birth. In acephalia falsa , hemic ephalia , and in microcephalia , the cerebrum is exposed and is frequently developed perfectly,
except in its volume. We can then hardly suppose that it has been
affected by external compression, or admit that when it is partially or
entirely deficient it has always pre-existed, and has been destroyed ;
but we have every reason to think, that in many such cases, any obstacle whatever, for instance, an accumulation of serum either within
this viscus or between it and the skull, has prevented its normal development, and has destroyed it. This conjecture is strengthened by
the analogy presented by the heads of monsters of this species with
those of children affected with hydrocephalus, by the traces of an
old or actually existing congestions of serum often found in membranous sacs hanging on the outside of the head : finally by a phenomenon which frequently occurs under the eye of the observer, the
change of hydrorachitis into the denudation and destruction of the
spinal marrow. As the cause of suspended development of the cerebrum, the abnormal accumulation of serum, is only the continuance at
one of the temporary degrees through which the organ successively
passes in its formation, it is easy to refute all objections made against
this theory by alledging that similar anomalies occur simultaneously
in other organs, that monsters which present instances of it are all
similar to one another, and that they are more common in the female
sex.(l) We however do not think that a mechanical obstacle of this
nature is always necessary, since the cerebrum is formed later than
the spinal marrow, and even when there is no external obstacle, it is
at first very small in proportion to the spinal marrow and the body,
and particularly its hemispheres appear last, and are at first proportionally very small.
(1) The observations of the ancients on this doctrinal point, are collected in Morgagni, De cans, et sed.morb.,ep. xii. (j. — Sandifort, Anat. inf antis ccrebro destitua. I.eyden, 1784. — Sœmmerring, Abbild,, und Beschreib, einiger Missgeburten, 1791.- — Meckel, Handbuch der pathol. Anatomie, vol. i. p. 193 — Tiedemann, Beobachtungen über Missbildungen des Gehirns und seiner Nerven ; in the Zeitschrift für Physiologie, vol. i. p. 56. Among those collected by the moderns, we shall mention the following-,
1st. Females. Pullin, in the Med. and. phys. journ., vol. i. 1799, no. 3, p. 224. — Id., ibid, vol. iii. 1800, no. 12, p. 138.— Pole, Case of extraordinary ma formation in a fetus ; same journal, vol. iii. no. 15, 1800, p. 397. — Beclard, in the Bullet, de la fac. de med., 1812. — Burrows, A case of malformation of the head ; in the Med. chir. trans., vol. iv. p. 52. — Lawrence, Accomil of a child born without a brain; same journal, vol. v. p. 165.
2d. Males. Cam, A case of monstrosity ; in the London med. and phys. journ., vol. vii. no. 39, 1802, p. 385.— Osiander, in the Gœtting. Anzeig., 1812, p. 1377, 1388. — • Kelch, Bcytrage zur patholog. Anatomie, Berlin, 1813, p. 83. — Account of four male children born without a brain ; in the London med. and phys. journ., vol. xxxiv. no. 198, 1815, p. 104.
3d. Undetermined. Two cases by Simmons, in the Lond. med. and phys. journ., vol. iv. no. 19, 1800, p. 189. — Two others by Beclard, in the Bullet, de la soc. de med., 1813, no. 1.
OF THE NERVOUS SYSTEM
499
From the extreme smallness and the denudation of the encephalon,
life is generally very short, continuing only for a few hours ; sometimes however, it remains several weeks. (1) When the wasting of
the'organ is not so extensive, the individual can live, but his intellectual
faculties are imperfect. Instances of this anomaly are seen in idiots(2)
and cretins ;(3) in them the cerebrum is characterized principally
by the smallness of its anterior and upper parts, or by its slight extent
from one side to the other, by which its height or its breadth(4) are
diminished.
It is still less probable that a diminution, a wasting of the encephalon, is attended with a diminution of the activity of the mind, since not only the nerves but the parts of the cerebrum to which they correspond, diminish and waste when their action has long been suspended.
Thus many anatomists, particularly Wenzel, (5) have noticed the wasting of the optic beds, and Gall of that of the anterior tubercula quadrigemina in blind people. Wenzel has determined by very minute researches, that in blindness the optic beds first flatten and then become narrower and shorter.
b. Sometimes the whole central mass of the nervous system or some one of its parts, are larger than when normal. Here, as in similar anomalies of the vascular system, we must distinguish simple dilatation from real enlargement.
Simple dilatation occurs in dropsy of the ventricles where the cerebrum is enormously distended, but is only a few lines thick ; and when the congestion of serum is very abundant, its mass is even smaller than in the normal state.(6)
But the cerebrum in children affected with rachitis presents on the contrary an abnormal enlargement in mass. (7)
(1) We have collected the cases of this kind in our Handbuch der pathol. Anatomie. To those already mentioned, we may add the following : Harder ( Pceon et Hythag., p. 125, c. 22.) mentions a child with this affection which lived ten days. Osiander ( Gcetting . Anzeig , 1812, p. 1387, 1388) has seen a boy in whom the medulla oblongata and the cerebellum were regular, and the cerebrum was but a slight rudiment, although possessing small cavities and the cortical and medullary substance, which lived fifteen days : it enjoyed good health during twelve, and died from the consequences of a disease of the mother. Lawrence {Med. chir. trans., vol. v.) mentions a female child who lived four days, and Burrows {Ibid., vol. ii.) another who existed six days.
(2) Rœderer, De cerebro observ., Goettingen, 1758, p. 5. — Greding. loc. cit., vol. iii. p. 594. — Siebold, Journal fur Geburtshülfe, vol. i. part ii. 259-265, 272-278.
(3) Wenzel, XJeber Cretinismus, Vienna, 1812.— Ackermann, lieber die Oretinen, Gotha, 1790.
(4) We find the skulls of idiots and cretins which possess an analogous formation of the cerebrum figured in Prochaska, Disq. org. corp. hum., Vienna, 1812, tab. 8-10. — Blumenbach, De nisus format, aberr., Goettingen, 1813, tab. 2.
(5) Depenit. struct, cereb., p. 125.
(6) Home, Observât, on the functions of the brain ; in the Phil, trans., 1814.
(7) Ludwig, Adv. méd. pr., vol. ii. p. 221.
The spinal marrow is sometimes larger than usual in spina bifida , as it is then found entirely filling the vertebral canal.(l)
The increase of some parts of the central mass of the nervous system is rather a rare phenomenon. Sometimes however we find the fourth lobe of the cerebellum, (2) the pineal gland, (3) the pituitary gland, (4) the optic beds, and the corpora striata, (5) larger than usual.
This anomaly is not always essentially the same. Hydrocephalus, the enlargement from rachitis, the abnormal length of the spinal marrow, the largeness of the prolongations, and of the pituitary gland, should undoubtedly be considered as a continuation of development after a type which is regular only in the early periods of life, since it is easy to demonstrate that these phenomena are normal in the early periods of existence.
The abnormal enlargement of the optic beds seems intended to compensate for the wasting of one of these two eminences, as these two states are usually seen simultaneously.
4th. The cerebrum and the spinal marrow rarely present primitive deviations of formation not included in one or another of the preceding classes.
In spina bifida the spinal marrow is sometimes flatter and broader, than usual, or even divided into two halves, which manifestly indicates a suspension of development.
Among the deviations in the formation of the cerebrum, we may arrange the following :
a. The mutual and perfect adhesion of the two hemispheres which is observed without any injury of the intellectual functions, and which sometimes occurs in all the inner faces of the hemispheres, (6) sometimes is confined to some points of these same surfaces, (7) which remarkably increases the number of the commissures when, as in the cases cited in the note, the two halves of the cerebrum are continuous. An arrangement similar to this is where there is an intimate adhesion of the inner faces of the hemispheres by a close cellular tissue.(8) In both cases the large cerebral falx is more or less imperfect. The de ficiency of this prolongation of the dura-mater, (9) the first degree of which, the existence of one or more openings which pass through it in different parts, and which is quite common, is curious as an analogy with the formation of most animals.
(1) This has been observed several times by Laenncc.
(2) Kelch, loc. cit., p. 90.
(3) Blane, in Trans, of a soc.for the improv. of med. and surg. knowl., London, vol. ii. p. 16.
(4) Greding, loc. cit., vol. ii. p. 515.
(5) Wenzel, loc , cit., p. 125, 126.
(6) Carlisle, in the Trans, of a soc.for the improv. of med. and surg. knowl., vol. ii.
p. 212 .
(7) Wenzel, loc. cit., p. 288.
(8) G reding', loc. cit., vol. iii. p. 630.
(9) Gunz, De lapillis gland, pinealis, p. xi.
OF THE NERVOUS SYSTEM,
501
b. Defect in symmetry , the obliquity of the cerebrum, which involves
a corresponding obliquity of the head and often also mental alienation,
(1) although this latter does not attend it necessarily. This defect
sometimes exists to such a degree that, at least if we may judge from
appearances, one half of the cerebellum is twice or three times as large
as the other.(2)
Wounds of the central part of the nervous system endanger the life of the person wounded, and the more the-nearer they are to the medulla oblongata.(3)
1809. Alterations of texture. We may arrange under this head the following alterations :
1st. Differences in consistence. The spinal marrow has been studied but slightly in this respect.
The degree of consistence of the cerebrum is not always perfectly the same, nor are the anomalies presented by it always attended with the same derangements of the intellectual faculties.
a. Induration. (4) Of this there are several degrees. If very extensive, the tissue of the cerebrum is at the same time more or less altered, and earthy particles(5) are even mixed with it. When this occurs, it is sometimes hard to cut the cerebral substance at those places where the induration exists. The cerebrum not unfrequently becomes more consistent in mental alienation,(6) and the intellectual faculties are more affected the greater the hardness of the cerebrum. (7)
b. Softening. (8) The induration of the cerebrum, notwithstanding the facts we have mentioned, is in general so slightly a necessary condition of mental alienation, that we much more frequently find the contrary state, the softening of the organ ; excellent observers who have had opportunities of seeing, have determined this fact.
(1) Greeting’, loc. cit., vol. ii. p. 525, 595, vol. iii. p. 453.
(2) Greeting, loc. cit., vol. ii. p. 525.
(3) See the excellent memoir of Casper, Sur les lesions de la moelle épinière, par rapport à leur degre de lethalité ; in the journ. compl. du Diet, des sc. med, vol. xvi. p. 309, vol. xviii. p. 107.
(4) S. Pinel, Recherches d' unatomie pathologique' sur V endurcissement du système nerveux ; in the Journ. dephys. ex p., vol. ii. p. 191.
(5) Morgagni, Desed.et caus. morb., ep. an. i. 10, 17, viii. 14. — Marshal, Morbid anatomy of the brain in mania and hydrophobia, London, 1815. Sixteen times in twenty-four cases.
(6) We find two cases in Home, loc. cit.— Portal, Anat. med., vol. iv. p. 110.
(7) Greding, loc. cit., vol. ii. p. 533, vol. iii. p. 662.
(8) The softening of the cerebrum is a subject of important research to the
French pathologists, a very general picture of which would be too extensive for a place here. We refer to the article cephalite in the Dictionnaire des sciences medicales, and to the good remarks of Lallemand. See also Rostan, Recherches sur le ramollissement du cerveau, Paris, 1828. Wc will only remark that Lallemand considers this morbid organic alteration as the result of inflammation of the cerebrum. His opinion is that which is most followed in France, where it is almost universally adopted. No one now denies, that in most cases of ataxic diseases, that is, with complicated symptoms of excitement and of diminution of the action of the encephalon, where the encephalon is found perfectly regular, more or less extensive softening of the cerebral substance appears. F. T.
502
DESCRIPTIVE ANATOMY.
The consistence of the cerebrum also is very commonly increased
in some parts, and diminished proportionally in others, but in subjects
affected with mental derangement/ 1) and with dropsy. (2) This state
of the cerebrum is even common in fools. (3)
But none of these states are necessarily connected with idiocy in general, or with its different species in particular, for the cerebrum has been found of the normal consistence in every species of mental derangement/d)
The cerebrum has been found much harder or softer than usual in subjects whose intellectual faculties were unimpaired. (5)
The cerebrum in idiocy has been found not only more or less consistent than usual, (6) but often of a normal consistence, or uncommonly soft, or finally too soft in some parts and too hard in others. (7) So too in madness it has been found too soft(8) and too hard.(9)
2d. Drops y. Dropsy of the centre of the nervous system ( hydro rachitis and hydrocephalus) is very common, especially in the early periods of life, and is often congenital. We have every reason to think that in this case it arises from suspended development.
In hydrorachis the serum is generally accumulated around the spinal marrow, most generally between it and the arachnoid membrane, more rarely between this membrane and the dura-mater, very rarely or even never between this membrane and the bones. When the congestion exists in the greatest degree, it opposes the development of the arches of the vertebrae to a greater or less extent, either in one or in several points, where the serum accumulated in the vertebral canal distends the membranes and the skin so as to form a tumor which is more or less prominent, and which finally breaks. (10)
Most generally hydrorachis is attended with hydrocephalus, which is generally distinguished into acute and chronic. (11) The congestion
(1) Home, loc. cit.— Portal, loccit., p. 110.
(2) Portal, loc. cit., p. 75.
(3) Greding, loc. cit., vol. iii. p. 064, 665.
(4) Greding, loc. cit., vol. ii. p. 532, 533, vol. iii. p. 662.
(5) Morgagni, De cans, et. sed. morb., ep. viii. 18, Ixi. 8.
(6) Meckel, Recherches anat. phys. sur les causes de la folie ; in the Mem. de Berlin, 1764, obs. 1-6.
{7) Greding, vol. ii. p. 557, vol. iii. p. 662, 665.
(8) Meckel, loc. cit., p. 71.
(9) Greding, loc. cit., vol. ii. p. 537, vol. iii. p. 664, 665. — Home, loc. cit. — Portal,
loc. cit.
(10) This tumor is most frequently situated in the loins, more rarely in the back, often in both of these places at once, rarely in the neck, rarely also in the sacrum, where it has been seen among others by Vrolik ( Mémoires sur quelques sujets interressans d'anatomie et de physiologie, trans. by Fullot, Amsterdam, 1822, p. 761.)
F. T.
(11) Breschet, Recherches anatomiques et chimiques sur une hydrocéphale chronique ; in the Juurn. de physiol, experimentale , vol. i. p 93 — Id.. Noie sur deux enfans
nouveau nés hydrocéphales et manquant de cerveau, same journal, vol. ii. p. 269. —
J. L. Brachet, Essai sur l'hydrocéphalite, ou hydropise aiguë des ventricules du
cerveau. Paris, 1818. — Coindet, Mém. sur l'hydrocéphale, Geneva, 1817. — Bricheteau,
Mémoire sur l'hydrocéphale interne ; in the Journ. compl, dessc. méd., vol. v. p. 193.
OF THE NERVOUS SYSTEM.
503
of serum is situated sometimes in the cerebral ventricles ( hydrops cerebri, hydrenc ephalus) , sometimes on the surface of the brain between the
arachnoid membrane and the dura-mater ; finally sometimes and most
commonly in both these parts ; in all these cases the arachnoid membrane is that which is primitively diseased. The cerebrum itself is
always more or less softened. When the serum is accumulated principally or solely in the ventricles, these cavities are dilated in proportion to its quantity, the substance of the cerebrum becomes thinner,
and the circumvolutions are flatter. The latter are finally entirely
defaced, when the cerebrum is distended and is considerably thin.
When on the contrary the serum is collected on the surface of the
brain, the latter collapses in proportion to its quantity.
The mass of the cerebrum is less than in the normal state, at least when there is a considerable congestion of serum, and when it takes place slowly.
Notwithstanding the normal communication between the cerebral ventricles, the serum is accumulated sometimes in only one of these cavities,(l) which proves that the openings have been obliterated by ah inflammatory effusion, and not as is pretended(2) that they do not exist.
Chronic hydrocephalus is most generally congenital, and probably even original. It depends then on the cerebrum continuing to grow after a type of first formation. (3) This is perhaps, at least in part, the reason why it often continues so long without necessarily deranging the intellectual faculties, even as the rupture of the septum of the heart is fatal, while its original perforation seems not to endanger life, which continues sometimes to an advanced age notwithstanding this anomaly.
3d. Inflammation. The substance and the envelops of the encephalon and spinal marrow may be inflamed. They then receive move blood than usual.
Wenzel has asserted that the pituitary gland always presents traces of irlflammation and its consequences in idiopathic epilepsy. (4) Presented in this general manner the assertion is false, as is proved by the facts collected by several observers, (5) and by ourselves.
vol. vi. p. 302, vol. vii. p. 97. — John, Recherches chimiques sur la liqueur que les ventricules du cerveau renferment dans l’hydrocéphale ; same journal, vol. vi. p. 270. — Consult also Coutanceau, Des épanchemcns dans le crâne pendant le cours des fièvres essentielles , Paris, 1802, the excellent article Hydrocéphale by Itard, in the Dictionnaire des sciences médicales , the article Hydrocéphale by Boisseau, in the Dictionnaire abrégé des sciences médicales , and Ducrot, Essai sur la céphalite, Paris 1812.
(1) Tulp, Obs. méd.. i. c. 25. — Wepfer, Obs. anat .de apoplexie, Schaffousne, 1675, p. 68. — Portai, Mém., vol. ii. p. 58. — Monro, On the brain, p. 18.
(2) By Portal among others.
(3) See our Handbuch der pathologischen Anatomie, vol. i.
(4) Observations sur la glande pituitaire dans l'épilepsie, Paris, 1S11.
(5) For instance Kelch, loc. cit., p. 103.— Otto, Seltne Beobachtungen, 1816, p. 106.
504
msscKirxivE anatomy.
Among the membranes the arachnoid is particularly liable to inflame. Hence the results of inflammation are observed most frequently
in it.( 1 ) Here we include,
a. The thickening of its substance, the result of exsudation.
b. The formation of yellowish white corpuscles, the glands of Pacchioni which are developed in several regions, particularly in the sinciput, and which are seen more particularly in maniacs and persons who have been subject during life to congestions of the brain. (2)
c. The effusion of pus between the parts of the arachnoid membrane which line the dura-mater and the pia-mater.
d. Very probably the abnormal new formations, ossification, &c.
The inflammation of the cerebral substance(3) is very remarkable,
particularly in respect to its consequences, inasmuch as not unfrequently this substance is destroyed even to a very considerable extent, although for a long time such a disorder has caused no marked derangement in the functions of the cerebrum, and has not manifestly endangered the life of the patient.(4)
Sometimes the pus found in the cerebrum is contained in special cysts, (5) which phenomenon cannot be explained better than in saying that it is not the cerebral substance which separated, but an accidental tissue developed within it, fox',
a. The cysts adhere but slightly to the cerebral substance which surrounds them.
b. The latter is not hardened but softened around them. (6)
(1) Parent-Duchateletand Martinet, Recherches sur l'inflammation de V arachnoïde cérébrale et spinale, Paris, 1821. — Deslandes, Examen des diverses formes que peut prendre la phlegmasic des méninges , Paris, 1817.
(2) Meckel, loe. cit., p. 77. — Greding, loc. cit, vol. ii. p. 471. — Wenzel, Prod., cap. i.
(3) Inflammation of the substance of the cerebrum has been termed encephalitis, or cerebriiis and cercbcllitis, when confined to the cerebrum or cerebellum (Lallemand, loc. cit.) ; that of the spinal marrow is termed myelitis, which is a better term than rachialgia and spinitis (Klohs, Diss. de myelitide, Halle, 1820 — Harles, TJeber die Entzündung des Rückenmarks. — Clot, Recherches el observations sur le spinitis, Montpellier, 1820. — Brera, Della rachialgite ; in the Atlidcll' accademia di Livorno, 1810. — Bergamaschi, Osservazioni sull’ inflammazionc della midolla spinale , Pavia, 1810). In the encephalon and even in the spinal marrow, inflammation seems usually to cause the softening and sometimes the induration of the medullary substance with the formation of abnormal tissues, or at least a tendency to this formation. It would seem as if this last effect, that is, induration, is more particularly the result of a slow, or as is generally termed, a chronic inflammation. P. T.
(4) Since inflammation of the cerebrum has been more studied, we know better
what to think of these cases. A softening of a few lines in diameter seems to cause death. If the same is not true, at least promptly, of a schirrous or even a cancerous change, it isjbecause they take place slowly, and we may consider as a law of the organism, in the state of disease, that an alteration even extensive but slow, destroys life less surely and less rapidly than another less extensive but acute. P. T.
(5) Bateman, Case of an encysted tumor, occupying the greater part of the right hemisphere of the brain ; in the Edinb. med. andsurg. journ., vol. i. p. 150.
(6) Brodie, Case of abscess in the brain; in the Trans, of a soc.for the improv. of med. andchir. knowl., vol. iii. p. 106.
OF THE NERVOUS SYSTEM.
505
4th. New foliations. Beside these alterations in the consistence of
the cerebrum, which are mentioned above and which supervene, although none is observed in the texture, the composition, and the color
of this viscus, the centre of the nervous system is frequently also the
seat of entirely new formations. These formations constitute a series
of pathological changes which commence by manifest alterations of
texture, which however unite with the rest of the mass, and which
terminates by more or less distinct bodies which adhere but slightly to
this mass.
The cysts filled with a fluid analogous to serum or thicker should probably be considered as the first degree of these new formations, since the concrete fluid they contain has no determinate character. These cysts appear both in the substance of the cerebrum, cerebellum, and medulla oblongata, (1) and on their surface between the meninges and in the ventricles. (2) Those in the cavities of the ventricles are very common in the choroid plexuses, which are, generally speaking, the most usual seat of their development. They generally have thin parietes ; but sometimes also, the membranes which form them are several lines thick. They are generally attached but feebly to the adjacent parts.
They vary much in size, from a head of a pin to a hen’s egg. The largest particularly, and those situated in the cerebral substance, are almost always isolated, but the small, those developed externally and in the cerebral ventricles, are united in a greater or less number.
The abnormal repetitions, of normal tissues, other than that of the serous tissue on the surface or in the substance of the cerebrum, are rare. They perhaps occur only in the cartilaginous and osseous tissues.
The abnormal ossifications are most frequently situated in the arachnoid membrane, and occur like all the formations of this kind in advanced age. They seem to be rarer in the spinal than in the cranial portion of this membrane.(3) We have every reason, however, to believe that this difference depends in great part on the fact, that the spinal marrow is examined less frequently than the cerebrum, for Morgagni has seen them once, and we have observed them twice in this region. They assume the form of thin and irregular layers, which project more or less above the surface of the arachnoid membrane, and are found principally on its posterior side and its lower part, to which they often adhere but very slightly.
They are developed on the surface of the cerebrum, between the dura-mater and the arachnoid membrane ; at least they almost always
(1) Portal, loc. cit., p. 72.— Morrah, A case of hydatids in thebrain ; in the Med. chir. trans., vol. ii. p. 262. — Home, loc. cit., p. 54.
(2) Buchanan, Case of encysted tumor of the brain; in the Edinb. med. journ., vol. viii. p. 276.
(3) Morgagni, De sed. et caus. morb., ep. 25, a. 9.— Sabatier, Sur quelques particularités de la moelle épinière et de ses enveloppes ; in the Mén. de Paris, 1783, p. 75. — Hertel, De cerebri et meningum tumoribus, Berlin, 1814.
Vol. II, 64
506
DESCRIPTIVE ANATOMY,
form on the inner surface of the first, that is to say, in fact, on the external arachnoid membrane which lines it. Those which are considered as belonging to the pia-mater,(l) are always formed not from
this membrane, but from the layer of the arachnoid membrane which
covers it, since they are found on the external face of the pia-mater,
and often adhere very strongly to the inner face of the dura-mater.(2)
They vary much in their number, extent, figure, and degree of adhesion. Sometimes they are insulated, sometimes expanded in several
parts, sometimes scarcely perceptible, and again several inches broad,
smooth or rough, with even or serrated edges, sometimes adhering by
a broad base, and sometimes only fitted to the membrane, to which
they are attached only by a few filaments. Their situation is the only
thing in regard to which certain generalities can be established with
precision. They are most generally found on the large falx, or at
least very near this fold, along the superior longitudinal sinus. Their
influence on the cerebrum depends on the circumstances mentioned
above, on the age of the subject, or on his greater or less susceptibility.
Besides these accidental ossifications, the tissue of the arachnoid
membrane is sometimes, but more rarely, changed in an analogous
manner. It becomes thicker, harder, and cartilaginous. (3)
The ossification of the cerebral substance itself, or the development of osseous substance within the cerebrum, is on the contrary a very rare phenomenon. Very probably, in most of the cases where it has been admitted, there were only exostoses of the bones of the skull, which projected within this cavity, and caused the crowding or destruction of the encephalon. Sometimes, however, earthy substance has really been found accumulated in the cerebrum in so great quantity, that it was difficult to divide it with a cutting instrument^) osseous concretions entirely distinct from the cerebral substance, have also been found, which were formed within it ;(5) finally, bone andcar
(1) Greeting, loc. cit., vol. ii. p. 483, 485, voî. iii. p. 626, 628.
(2) Gredings loc. cit., vol. ii.
(3) Greeting', loc. cit., vol. ii. p. 484. — F.squirol, in the Tlull. dé la fac . de Tried., voL V- p. 426.
(4) Home (loc. cit.) has observed tills peculiarity in the annular protuberance of a boy, an idiot from birth, and who at sixteen years, when he died, was only about the height of a child three years old. Andral has found in an individual who died of phthisis, on the upper surface of the left hemisphere, not far from its anterior extremity, and near a large fissure, a granulation of the volume of a large pea, having the consistence of calcareous concretions of the lung, and penetrate into the cerebral substance which they crowded ; but perhaps it was only the ossification of the arachnoid membrane. (Journal de physiologie experimentale, vol. ii. p. 110.) The same observer has found a kind of fibro-cartilaginous change of several circumvolutions of the two hemispheres of the cerebrum; the latter resisted like the fibro-cartil a <res when pressed between the fingers. In pulling them they are elongated, and then contract, and are very elastic ; they had the color of ivory, but no trace of the gray tint. Such indurations existed in the thickness of the hemispheres, and at their base (loc. cit.). The cartilaginous induration of the 3pinal marrow has beeca observed also by Bergamaschi and Portal.
(5) Grcding, loc. cit ., vol. iii. p. 668, in the cerebellum.
OF THE NERVOUS SYSTEM.
507
tila-ge have been met with in a cyst developed in the midst of the cerebral mass.(l)
Tt is not unfrequent to find, particularly in the cerebrum, entirely new formations, assuming the form of rounded tumors; but they are rarely or never developed in this viscus alone, and they are generally only portions of a mass of the same morbid formation existing in most of the other organs.(2) They differ from each other so much in respect to consistence, volume, number, and connections, that they must necessarily be referred to different species, between which, however, numerous intermediate degrees exist, as between all new and abnormal formations generally.(3)
In respect to color , these masses are whitish, of a yellowish white, (4) reddish, (5) of a tint similar to that of cortical substance, (6) of a deep red, {7) or red and streaked with white. (8)
They are generally extremely solid, (9) whence they are often termed schirrous. Sometimes, however, they are spongy and soft, of a tissue which is soft and similar to that of the spleen. (10)
Sometimes they are homogeneous,(ll) sometimes more or less evidently fibrous, (12) and composed of several rounded bodies.(13)
They sometimes become quite large, and have a diameter of from two to three inches.( 14) Sometimes they are single, (15) sometimes more or less numerous.(16)
j( 1) Hutchinson, Case of disease in the brain ; in the Med. chir. trans., vol. iv. p.
202 .
(2) Reil, Memorab. clin., vol. ii. f. i. p. 39.- — Portal, loc. cit , p. 92. — Earle, A case of diseased testicles. , accompanied with diseases of the lungs and brain; in the Med. chir. trans., vol. iii. p. 57 — Merat, in the Journ. de med., vol. x. p. 3.
(3) Among- these tumors there are some which must be referred to the schirrous
and encephaloid tissues, which Andra.1 has observed once, both crude and softened from the level of the optic beds to near the base of the cerebrum (Note sur le cancer du cerveau, in the Journal dephys. exp., vol. ii. p. 106). Hitherto Bayle is the only one who has well described the cancer of the cerebrum. We know as yet of no well authenticated case of cancer of the spinal marrow. Guersent, Pincl-Grandcbamp, however, mentions a case of cancer of the medulla’oblongata, which had principally destroyed the pyramids and olivary bodies (Ollivier, De la moelle epiniere et de ses maladies), and Andral (loc. cit.) has also found numerous tubercles in the cerebrum of a man who died of pleurtic effusion. Some were already suppurated and surrounded with softened cerebral substance. F. T.
(4) Portal. — Reil. — Hutchinson. — Morgagni, loc. cit , vol. xii. p. 15. — Bateman. — Baillie, — Ozanam, Observations sur une affection tuberculeuse du cerveau-, in the Journ. comp, du Diet, des sc. med., vol. xix. p. 189.
(5) Merat,— Salter, Case of disease in the brain ; in the Edinb. med. journ., vol. ii. p. 469. — Morgagni.
(6) Steinhach.
(7) Earle, p. 67. — Buchanan, Case of encysted tumor in the brain : in the Edinb. med. journ., voL viii. p. 276.
(8) Earle.
(9) Earle. —Portal. — Merat. — ReiL — Baillie.
(10) Buchanan, p. 279.
(11) Hutchinson.
(12) Salter.
(13) Morgagni.
(14) Merat. — Earle.
(15) Buchanan. — Merat. — Hutchinson.
(16) Merat, twice. — Salter, once. — Earle, seven times.
608
DESCRIPTIVE ANATOMY.
In certain cases they are imperceptibly continuous with the substance of the cerebrum, or at least adhere to it very intimately, but are.
not surrounded by a cyst.(l) In other cases they are slightty attached
to the cerebral substance, (2) or are inclosed in a special cyst, usually
with very thin parietes.(3)
These abnormal formations do not always continue in the same state during all their existence. It, is infinitely probable that they all tend sooner or later to suppurate, although death often occurs before this period, snd the greater or less facility with which they suppurate, has no relation with their size. When suppuration attacks them, they resemble sacs which vary in thickness and are closed or open. (4)
New formations of a similar character are developed also in the envelops of the centre of the nervous system.
Among the meninges, they are situated principally in the duramater. They are termed generally the fungi of the dura-mater, (5) although all certainly do not belong to the same class, as they differ much in texture and form. They do not generally attack only the cranial portion of the dura-mater ;(6) observers entitled to credit, have also proved their existence in that portion of this membrane which lines the vertebral canal, (7) although there they seem to be less frequent in proportion.
Finally, we must place last the foreign bodies which are found principally within or on the surface of the central mass of the nervous system. Some arise from the greatest degree of the formative action, and these are the entozoaries. Others are liquids which are not always effused within or on the surface of the nervous system, from a change in its mode of action.
a. Entozoaries. The only intestinal worm which has certainly been known to exist in the encephalon is the cysticercus cellulosœ,(8)
(1) Reil. — Hutchinson. — Salter. — Morg-agni.
(2) Earle. — Steinbach. — Bateman. — Brodie. — Merat.
(3) Home, loc. cit., p. 51. — Merat. — Buchanan.
(4) Brodie. — Bateman.
(5) Louis, Sur les tumeurs fongueuses de la dure-mêre ; in the Mém. de Vac. de chir., vol. v. p. 1. — Wenzel, Ucber die schwammigen Auswüchse der harten Hirnhaut. , 1811. — Walther, Essai sur les fongus de la dure-mère ; in the Journ. compl. des sc. mcd., vol. vii. p. 118. — Esquirol, Tumeur considérable développée dans l'intérieur ducrânc ; in the Archiv, gêner, de méd., vol. iii. p. 594. — C. B. Tilanus, De fongosâ duree meningis cxerescente disserlatio, Utrecht, 1819. — Heusinger compares these tumors to those described by the Germans, as cephalomatoma, which have been mentioned in Michælis, Ucber cine eigene Art von Blulgescywülsten ; in Loder, Journ. für die Chirurgie , vol. ii. cab. iv. p. 657. — Nægele, Erfahrungen und Abhandlungen aus dem Gebiethe der Krankheiten des weiblichen Geschlechts , Manheim, 1812, p. 245. — C. Zeller, De cephalæmatomalc, seu sanguineo cranii tumore recens nalorum commentatio, Heidelberg, 1822.
(6) Wenzel, loc. cit., xxiii.
(7) Knox, in the Med. obs. and inq. vol. iii. p. 160. — Philipps, New med. journ., vol. i. p. 144.
(8) Steinbuch, Cogitata quœdam dé vermium visceralium physialogia , Erlangen, 1801.
which occurs principally in the internal and external pia-mater, particularly in the choroid plexuses of the cerebral ventricles. The serous cysts often found in these bodies are very probably connected with its formation.(l)
b. The second class of foreign bodies is composed particularly of sanguineous effusions.
Not unfrequently there is an effusion either of pure blood or of a more or less bloody serum, either between the meninges or in the ventricles, or in the substance of the cerebrum and spinal marrow, (2) or finally between the dura-mater and the skull. This latter case is rather rare in the skull, and most generally results from an external wound. Such an effusion results sometimes in the more or less perfect and transitory or permanent and fatal suspension of the action of the cerebrum, apoplexy , sometimes the paralysis of the voluntary organs, according to its quantity and the place where it occurs. (3)
(1) Of all the entozoaries, the cysticercus cellulosa is found most frequently in the
encephalon, where it sometimes lives in the cerebral substance (Zeitschrift fur die Anthopologie, 1823, part iii. p. 197) ; but Romberg has also found there acephalocysts, and Arnott the echinococcus hominis ( V. Romberg, Sur les entozoaires du cerveau, in the Journ. comp, du Diet, des sc. med. vol. xix. p. 276). Esquirol mentions the existence of acephalocysts in the cavity of the arachnoid membrane of the spinal marrow ( Bullet . de la Fac. de med., vol. v. p. 426). F. T.
(2) But little attention has been paid to effusions of blood in the spinal marrow,
where they are in fact rare. Home has found a clot of blood about two inches long in the centre of the organ, after a dislocation of the sixth cervical vertebra on the seventh (Phil, trans., 1814). This internal hemorrhage sometimes occurs spontaneously, and forms a circumscribed effusion similar to those in the cerebral substance in apoplexy, but it would seem not to have been observed until at present, except in the upper part of the spinal marrow, or rather in the medulla oblongata, and even only beyond it in the annular protuberance. Serres mentions several cases of it (Annuaire des hôpitaux, 1819). When these effusions are but of slight extent, they may be resolved like those in the substance of the encephalon. Pinel Grandchamp has found in the left half of the annular protuberance of a cadaver, evident traces of an absorbed effusion, that is, a circumscribed cavity filled with a filamentous tissue, infiltrated with yellowish serum : the cavity would contain a common sized bean. Ollivier has described and figured this case (loc. cit., p. 263. p. ii. fig. 3. a). GautierClaubry, however, has stated a case where there was an effusion of blood in a very great extent of the spinal marrow, which had become a semifluid reddish ball, similar to the deposit from red wine, and presented no trace of organization (Journ. gen de méd., 1801). F. T.
(3) Deep wounds, compression by a portion of bone, by a foreign body, by an effusion of blood, serum or pus, the softening of the nervous substance may cause apoplexy or paralysis. Rochoux assigns as the character of apoplexy, caused by an effusion of blood, its manifestation by sudden paralysis. Lallemand thinks that the paralysis supervening after the combined phenomena of excitement and collapse, is caused by softening which arises from inflammation. If paralysis supervenes after symptoms of arachnoiditis, it is probably caused by a serous, sero-sanguineous or sanguineous effusion, which, however, is situated in the ventricles or on the surface of the viscus. Serres, Flourens, Foville, Pinel-Grandchamp, and Lachampe-Lousteau, have attempted after Willis, Morgagni, and many others, to determine the exact relations between the phenomena of paralysis and of lesion of the encephalon or of the spinal marrow. Their researches are contradictory. It only remains proved, as it had been before they attended to it, that the lesion is always on the side opposite to that paralyzed, and that the sanguineous effusions, the softening of the fornix, of the corpus callosum and of the septum lucidum, do not cause paralysis. F. T
It does not necessarily suppose the laceration of the vessels ; but it often andapparently most generally arises from a sanguineous exsudation from the capillary vessels.(l)
The cerebral arteries, however, are more exposed to laceration than the others from their feebleness, and this lesion generally seems to attack the middle large cerebral artery, at the lower extremity of the fissure of Sylvius. (2)
We can easily conceive that an effusion of blood in the substance of the cerebrum and spinal marrow cannot occur without a rupture of the vessels.
These effusions seem to be more common in the corpora striata than in all the other parts of the cerebrum, on account of their softness : perhaps, however, it is more correct to say that those which occur in these eminences endanger life more than those in the other regions of the encephalon, especially in the hemispheres of the cerebrum where traces of old effusions are frequently seen. (3)
When effusion does not cause death, we find traces of it long afterward. Such are the simple or multilocular spaces filled with a deposit of blood or of liquid serum, coagulated or mingled with cellular tissue, and often covered with a serous cyst, which are found in the cerebrum of those who have survived long after an attack of apoplexy, or who have been deprived for a greater or less length of time of the use of their intellectual faculties. (4)
This is, in fact, the course most generally employed by nature to heal the ruptures of the cerebral substance caused by the effusions of blood. In the rarest cases the effused fluid is entirely absorbed, and the rupture of the cerebral substance is entirely closed by a solid cicatrix. (5)
(1) Wepfer, Hist, apoplect., p. 5. — Cheyne, On Apoplexy , London, 1812.
(2) Portal, loc. cit., vol. iv. p. 80.— Wepfer, loc. cit ., p. 8.
(3) Rochoux has found in bloody effusions eighteen on the left, eleven of which were within the corpora striata, seven on the right, eight of which were in the same part, finally six on the two sides, three of which were in the same place. F. T.
(4) Brunner, inth e Eph. nat. cur., dec. iii. a. i. p. 374. — Santorini, Obs. anat., iii.
Î 6.— Morgagni, De sed. et caus., ep. iii. 6. ix. 20, 23. — Cruveilhier, Anat. patkol., 'aris, 1816, vol. i. p. 205. — Rochoux, Recherches sur V apoplexie, Paris, 1814. This author was the first who treated well of the alterations of the cerebrum which attend or follow the effusion of blood in this viscus. But the cysts which are developed around, and are termed apoplectic, have been described well only by Riobe ( Observations propres d résoudre cette question : L'apoplexie dans laquelle il se fait un épanchement de sang dans le cerveau est-elle susceptible de guérison? Paris, 1814). — See also Bricheteau, Considérations et observations sur l'apoplexie : in the Journ. compl. dei sc. méd., vol. i. p. 129, 289. — Consult also the treatise of Lallemand.
(5) We have lately received a new work of Gmelin, who on analyzing the brain of man and the ox, concludes from his researches that the pulpy substance contains, besides a fluid fat body, two other kinds of fat bodies, viz : 1st. a lamellar substance, similar in every respect to cholesterine, except that it contains a mixture of phosphorus, the quantity of which has not yet been determined : 2d. a small quantity of a substance similar to wax : this latter is the most fusible of all the fatty bodies, and does not saponify ; it also contains a small quantity of phosphorus. (Tiedemann, G. R. Treviranus, and L. C. Treviranus, Zeitschriftfür die Physiologie, parti. 1824, p. 119). F. T.
Sometimes the cerebral ventricles are so filled with blood that the substance of the encephalon is finally torn, and the liquid is effused through this opening on its surface between the meninges.
An effusion of blood ( apoplexia sanguined) is not, however, necessary to produce apoplexy, since the latter frequently supervenes, from an accumulation of serum either in the cavities or on the surface of the cerebrum, as in apoplexia serosa, { 1) or even without any manifest change, as in apoplexia sine materia. {2)
(1) We have every reason to think that this apoplexy is an effect of arachnoiditis.
F. T.
(2) This apoplexia sine materia , is exactly that which presents so frequent instan ces of softening' of the brain. We may add to the three varieties mentioned by the author, the aploplexia convulsiva of some pathologists, which seems to be an inflammation of the encephalon, attended more or less promptly with a comatose state and with paralysis. F. T.
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