Meckel1812-1 Anatomy 2-3

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Meckel JF. Handbook of Pathological Anatomy (Handbuch der pathologischen Anatomie) Vol. 1. (1812) Leipzig.

Volume 1: General Anatomy. Part I | General Anatomy. Part II: 1 Mucous System | 2 Vascular System | 3 Nervous System | 4 Osseous System | 5 Cartilaginous System | 6 Fibro-Cartilaginous System | 7 Fibrous System | 8 Muscular System | 9 Serous System | 10 Cutaneous System | 11 Glandular System | 12 The Accidental Formations | Historic Embryology (1812)
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Handbook of Pathological Anatomy Volume I (1812)

Section III. Of the Nervous System

ARTICLE FIRST.

OF THE NERVOUS SYSTEM IN THE NORMAL STATE.

§ 135. The nervous system {systema nervosum){\) of man, and of most animals, namely, of all those which have a vertebral column, comprises two portions : the one, more or less globular, terminates in a prolongation similar to a tail ; it is inclosed in the cavity of the skull and spine. The other is composed of elongated fine rays, which ramify, and which, being attached to the former by their central extremities, are expanded through the whole body among the other organs, which are partly formed by their other extremity, or periphery. The first portion, called the central or internal, is composed of the brain, {encephalim) ,{2)

(1) Willis, Cerebri anatome nervorumque descriptio et usus, Geneva, 1676.— Vieussens, Neurographia universalis, Lyons, 1684. — J. C. Mayer, Abhandlung vom Gehirn, Rückenmarck und dem Ursprünge der Nerven, Berlin, 1779.— G. ProchsLsksL, De structura nervorum tractactus anatonnicies, Vienna, 1779. — Monro, Observations on the structure and the functions of the nervous system, Edinburgh, 1783. — Vicqd'Azyr, Recherches sur la stucture du cerveau ; in the Mémoires de l' academie des sciences de Paris, 1781, 1783. — Pfefflnger, Diss. de struciurà nervorum, Strasburg, 1782, 1783. — Metzger, Animadversiones anat. physiol, indoctrinam nervorum, Koningsberg, 1783. — Gallet Spurzheim, Recherches sur le système nerveux, Paris, 1819. — Carus, Anatomie und Physiologie des Nervensystens, Leipsic, 1814. — Wederneyer, Physiologische Untersuchungen über das Nevrensystem und die Respira<ton, Hanover, 1817. — Nasse, Ueber das verhaltniss des Gehirns und Riickenmarks zur Belebung des übrigen Körpers. Halle, 1818. — Georget, De la physiologie du système nerveux, spécialement du cerveau ; recherches sur les maladies reerveuses, etc., Paris, 1821.

(2) Malpighi, De cerebro ; in the Epist. anat. de cerebri cortice; ibid. — Vicq d'Azyr, Traité d'anat. et de phys., Paris, 1786. — J. and C. Wenzel, Depenitiori structura cerebri hominis et brutorum, Tubingen. 1812. — Reil, Fragmente über die Bildung des Gehirns-, in the Archiv für die Physiologie, vol. viii. ix. xi. — Rolando, Saggio sulla vera struttura del cervello deW uomo, Sassari, 1809. — Rosenthal, Ein Beytrag zur Encéphalotomie, Weimar, 1815. — Gordon, Observations on the structure of the brain, Edinburgh, 1817. — Burdach, Vom Bau und Beben des Gehirns, Leipsic, 1819-1822. — Tiedemann, Anatomie du cerveau, transi, by Jourdan, Paris, 1823. — Serres, Anatomie comparée du cerveau, Paris, 1824.


ÖF THE NERVOUS SYSTEM IN THE NORMAL STATE. 153

and of the spinal man'otv {medulla spmalis,){l) ; the other, the external or peripheric, is the nerves. (2)

Those nerves which arise from the brain are called the cerebrai nerves, {nervi cerebrales,) and those coming from the spinal marrow are called the spinal nerves {nervi spinales). The whole number is forty-two pairs, twelve of which are cerebral, and the other thirty spinal ; strictly speaking, however, there are only eleven pairs of cerebral and thirty-one of spinal nerves.

§ 136. It is in the nervous system especially that we discern that the body is composed of two lateral corresponding portions. In fact, all its parts are double, or when simple are placed near the median line, along which the two halves which constitute them unite, and blend in one mass. This arrangement is observed equally in the central portion, and in the periphery. At the same time the two lateral parts correspond exactly in all the nervous system, so that they vary less in situation, form, and volume, than other organs, and it is often impossible to perceive the least difference between them. This system is then symmetrical in the strictest sense of the word. The symmetry appears especially in the bram and spinal marrow, and the nerves which are immediately attached to these two organs. It is less marked in the great sijmpathetic nerve, a part of the system almost isolated from the rest. This difference deserves to be more attended to, because the symmetry of the organs corresponds exactly to that of the portion of the nervous system with which they are connected. All parts of the brain, the spinal marrow, and their nerves are not however equally symmetrical. The external is less so than the internal portion. Hence why the surface of the brain and the arrangement of the extreme ramifications of the nerves on the right and left sides differ more than the deep portions of the encephalon, and the origins of the nerves on both sides.

§ 137. The structure of the nervous system is also very constant. It is indisputably the system of organs in which we find the fewest anomalies. In this respect however the same difference exists between its parts as in the preceding ; for the great sympathetic nerve presents numerous and considerable variations in every respect, v/hile the internal parts, especially the origins of the nerves, are very constant. We have no mstance of a nerve arising from any other than its usual point ; unlike the vascular system, in which ano-malies, even of the largest trunks, are very common.

(1) Blasius, Medullæ spinalis anal., Amsterdam, lUôG. — J. J. Huber, De medullâ spinali, Gottingen, 1739. — G. C. Protsoher, Descriptio medullæ spinalis, Erlangen, 1788. — G. T. Kenffel, De medullâ spinali diss., Halle, 1810. — Racchetti, /leWa struttura, dxlle funzione e delle malattie della midolla spinale. Milan, 1816. — Ollivier. Essai sur l'anatomie et les vices de conformation de la moelle épinière, Paris, 1623. — Idem, De la moelle épinière et de ses maladies, Paris, 1823. — Rolando, Ricerche anatomiche sulla struttura del midollo spinale, Turin, 1824.

(2) Arnemann, Versuch über die Regeneration an lebenden 77ne7-e?i, Gottingen, 1787, vol. i. p. ii. p. 127-308. — Rcil, E.vercitationes anatomicœ de structura nervorum, Halle, 1797.

Vol. I.


20


154


GENERAL ANATOMY.


§ 138, Considered either in regard to symmetry or structure, the nervous system of man is less regular than that of other animals, even those which are nearest to him. This remark has already been made by Vicq d'Azyr ;(1) and the observations of Wenzel(2) prove its justice. In fact the halves of the nervous system correspond more perfectly in the mammalia, and the deviations from the normal state in these animals are rarer than in man.

§ 139. The nervous system is composed principally of semi-coagulated albumen. We find, besides, two kinds of fatty matter, a peculiar reddish-brown gelatinous substance, osmazome, phosphorus, sulphur, hydrochlorate of soda, and several phosphates. (3) The analysis of


the brain of man gives the following results :

Water - 80.00

Whitish fatty substance 4.53

Reddish fatty substance; called cerebrine - - - - - 0.70

Albumen 7.00

'Osmazome 1.12

Phosphorus 1.50

Salts and sulphur - - - 5.15


Total, 100.00

The spinal marrow and its upper part, the medulla oblongata, have the same chemical composition ; but they differ from the brain in containing more fatty matter, and more albumen, osmazome, and water.

In the nerves on the contrary, we find less fatty substance and more albumen than in the brain.(4)

§ 140. This system is mostly formed of a white and soft substance called the medullary substance^ {substantia medullaris.) This substance alone probably constitutes the nerves. In the central part of the system we find an abundance of another substance called the gray or cineritious substance, {substantia cinerea,) from its color, and the cortical substance {substantia corticalis,) because it forms the external layer of the brain, where it envelopes the medullary substance. Finally, the brain contains more or less of a third substance, the yellow substance, {substantia ßava,) and, besides these two, in some parts, even a fourth, the black substance, {substantia nigra ;) but properly speaking, these are simple modifications of one and the same substance.

§.141. Besides their difference in color, these substances vary from one another in many respects :


(1) Mem. de I'Acad. des sc., 1783, p. 470.

(2) Wenzel, Prodr. et Depenit. cer. struct., chap. iii.

(3) Fourcroy, in the Ann. de chimie, vol. xvi. p. 282-322. — Vauquelin, Analyse de la matière cérébrale de l'homme et des animaux, in the Ann. du Mus. d'hist. naturelle, vol. xviii. p. 212-239.

(4) Home, Observations on the brain and nerves, proving that their component materials exist in the blood, in the Philosoph. 'Pransact. 1821, p. 26. — Chevreul has detected cerebrine in the blood. — F. T.


OF THE NERVOUS SYSTEM IN THE NORMAL STATE


155


1st, In their proportional quantity. The medullary substance exceeds the cortical substance, although m certain parts of the brain the latter is more abundant.

2d. In structure. Their final elements of form are in fact the same ; but we remark in the medullary substance that they more evidently combine to produce secondary formations, as we shall show hereafter.

3d. In their physical qualities. The gray substance is softer and more fluid than the medullary substance ; it also diminishes more in drying.

4th. The gray substance receives more blood vessels than the medullary substance ; hence it has been considered as entirely vascular ; but this is not probable, since even the most successful injections do not change it into a tissue of vessels.

5th. The gray substance differs perhaps a little from the medullary substance in chemical composition. It is said not to contain phosphorus. (?)(1)

This substance is not similar in all parts. Thus it is paler in the tubercula quadrigemina than in the thalami optici ; paler too in the latter and on the surface of the brain than. in the corpora striata. The yellow substance is less abundant than the gray, and the band it forms between the latter and the medullary substance, is narrower than the gray stratum. Still the gray substance forms considerable masses in different parts ; for instance, in the centre of the cerebellum, in the corpus fimbriatum, and the eminentia olivaria. It is there also firmer than the medullary substance.

The black substance is foimd only in a few parts. There is also in some parts a bluish substance. (2)

§ 142. The structure of the nervous system is every where the same, at least in its essential characters. Its remote elements of form are globules, united by a semi-fluid substance. (3) These globules are found both in the medullary and cortical portions, in the brain, spinal marrow, and in the nerves. Opinions vary in regard to their form and size, and to the degree of consistence of the substance which unices them.

§ 143. According to Della Toire, these globules differ in volume and transparency in all parts of the nervous system ; the largest being found in the cerebrum so called, the next in size are those of the cerebellum, while those of the medulla oblongata are still smaller, although larger than those of the medulla spinalis ; the smallest and most opaqcte are found in the nerves ; even in these they vary in size, diminishing continually from the origin of the nerves to their terminations. The globules of the cortical, are always larger than those of the medullary, substance.

(1) John, Chemische Tabellen des Thierreichs, Berlin, 1814, p. 74.

(2) Wenzel, loc. cit. chap. 16.

(3) Della Torre, Nuove osservazioni microscopiche, Naples, 1776, p. 16-21. — Prochaska, De structura nervorum, Vienna, 1779, sect. ii. c. 10. — Wenzel, loc. cit. chap. iv. — A. Barba, Osservazioni microscopiche sul cervello e sulle parti adjacenti Naples, 1807. — Home and Bauer, in the Phil, trans., 1821.


15ü


GENERAL ANATOMY,


Prochaska aiul Barba on the contrary think tliat the globules are of Ute same size in every part of the nervous system ; and that the difference remarked by some depends on the difficulty of separating from each other.

Prochaska estimates their size at one eighth of those of the blood ;(1) but he thinks they are not all similar in this respect, even in one and the same part.

It has not yet been ascertained whether they differ regularly at different periods of life, as has been observed in certain animals. (2)

§ 144. They are not perfectly round. Whether they are hollow or solid has not yet been determined ; because, from their smallness, and from optical deception, this part of then history is ascertained with difficulty.

§ 145. According to Prochaska, these globules are united by a delicate cellular tissue. Della Torre thinks, however, that it is by a transpareirt viscous fluid, more tenacious in the medullary than in the cortical substance. In the different ]rarts of the nervous system the viscidity of that which belongs to the medullary substance increases in the same ratio as the size of the globules decreases.

Barba says, however, that this difference is only imaginary, and depends on the length of time which elapses between death and the moment of observation.

§ 146. These two elements of form unite in all parts of the nervous system, giving rise to fibres, most of which are longitudinal.

§ 147. In no system is this fibrous structure more apparent than in the nerves. Almost all the nerves are formed of a greater or less number of fasciculi, visible to the naked eye, these are composed of smaller cot'ds,{funes) and these again of minute filaments {fila.) The fasciculi, cords, and filaments ramify and anastomose extensively ; and we cannot find a single fasciculus which extends any distance in a straight line. At the ends of the nerves these ramifications and communications are fewer than in their course. The size of the filaments and cords formed by them differs not only in different nerves, but even in the same nerve. Their diameters vary from one tenth of a line to several lines. They are thicker in the body of a nerve than at its extremities, where they separate and become smaller. All the nervous fasciculi, whether formed of large or small collections of fibres, follow the longitudinal direction of the nerve.

§ 148. The medulla of the nerve is not loose. Each filament, even the smallest, has a special sheath which closely envelopes it, and which is formed hke the filament. Hence when the medullary substance is removed by an alkaline solution, the tunnels represent the form of the entire nerve, and the medullary substance exhibits the

(1) Loc. cit. p. 72.

(2) Carus thinks that the g-lobules are arranged in masses in the central portions, and in regular lines in the nerves. Milne Edwards determined that the nervous substance of the encephalon, of the spinal marrow, and of the nerves in the four classes of vertebral animals, is formed of globules of of a millimetre united iu a series so as to form primitive fibres M-hich are considerably long. — F, T.


OF THE NERVOUS SYSTEM IN THE NORMAL STATE


157


Käme appearance when its tunic is removed by immersion in an acid.(l) The alkalies dissolve the pulp, which may be pressed out easily, so that having tied the nerve and filled it with mercury or air, and dried it, the canaliculated structure becomes apparent. On the contrary, the acids destroy the sheath and harden the fibres, the finest of which then become visible to the naked eye.

§ 149. The nerve then is composed of two substances, a medullary portion and the canals which inclose it. These canals are formed of mucous tissue, and are called neurilemma, a term derived from their relation to the medullary substance. The neurilemma envelopes the whole nerve, and generally we can suppose it furnished internally with .folds which continually diminish. It receives numerous vessels which divide, at right angles, into two trunks, one straight, the other retrograde ; these frequently anastomose together.

The neurilemma is very firm and difficult to tear. It appears to be the secretory organ of the medullary, with which its relations diminish at the two extremities of the nerves. Near the central termination it disappears within the nerve sooner than on the surface, so that the collection of the neurilemmatous canals forms a considerable depression towards the brain and spinal marrow.

§ 150. Besides the fibrous structure of the nerves and their formation by two substances, the pulp and neurilemma, and the irregulaiity of form which results from tliis circumstance, their external surface is banded and undulated, and hence appears uneven. (2) By the naked eye we observe on the surface of the nerve, and with a microscope, in the cords which compose it, spiral bands which are directed obliquely in zigzag. This appearance vanishes when the nerve is extended, but is again perceptible when the extension ceases.. It disappears entirely in the morbid state, or at least in nerves softened or decajmd, either from maceration or from the effect of alcohol. It doubtless depends on a folding which takes place when the nerve shortens, on account of its slight contractility. It is principally seated in the neurilemma, for it is not well marked in those nerves which are soft, and those furnished with a feeble sheath, as the olfactory nerve. (3)

(1) Reil, De structura nervorum., p. 3-17. — Osiander, Epigr.in compl.museianat. res., Gottingen, 1807, p. 51.

r (2) Molinclli, Comment. Bonon., vol. iii. p. 280. — Fontana, Sur la structure des ■nerfs; in his Obs. sur les poisons, vol. ii. — Monro, loc. cit. chap. 12, 13. — Arnemann, loc. cit. p. 147-174.

(3) Prévost and Dumas have published some observations on the structure of the nerves, which we shall here mention. They state that the nerves have a satinlike appearance, which was first completely and exactly described by F ontana. It is very smooth, especially in the nerves of the cat, rabbit, guinea pig, frog, &c. When examined with a magnifier of ten or fifteen diameters only, we then see on their surfaces alternate white and dark bands, which frequently resemble the turns of a spiral spring which might be placed under the neurilemma. This appearance, like that of the tendinous tissues, depends on a slight folding of the fibres of the neurilemma, which loses its transparency in some parts, and retains it in others. Those which are opaque reflect all the light which strikes on their surface, and the others on the contrary allow it to pass in sufficient quantity to render visible the colored bodies placed under the nerves. When we attempt to draw it out, all this appearance


158


GENERAL ANATOMY,


§ 151. All nerves are not formed exactly after the same type, and probably the modifications observed in this respect depend on differences in their mode of action. These differences relate to their inner structure and their configuration or external form.

Modifications of the inner structure may depend either on the medullary substance, or the neurilemma ; but it is probable that in most cases both are concerned. They are —

1st. Differences in solidity and hardness. Generally, the nerves which go to the heart, the large vessels, and to the abdominal viscera, the auditory, and particularly the olfactory nerves, are much softer than the others. We find scarcely a trace of the neurilemma in the olfactory nerve. On the contrary, the fasciculi of the optic nerve are, proportionally speaking, much larger than those of the other nerves. Very probably, then, this difference depends not only on the greater or less consistence of the medullary matter, but also on the arrangement of the neurilemma.

2d. Differences in color. The nerves of the heart and abdomen, and the olfactory nerves, are mostly reddish, and not white like the others. There is even a gray substance in the centre of the olfactory nerve.

3d. Differences in the arrangement of the nervous cords and filaments. Their size varies, but not in proportion to the volume of the nerves. The cords of the principal nerves of the inferior extremity, for

vanishes, and if we divide the neurilemma we find nothing resembling it. It would not then deserve notice if it did not offer a very certain mark to recognize the small nervous filaments, and render it easy to distinguish them from the blood-vessels or the lymphatics. But when we take a nerve, and, dividing its neurilemma longitudinally, draw out the' pnlpous matter under water, we find it composed of numerous email parallel filaments of equal size, and which seem to be contained in the whole nerve. At least we never see them unite or divide, whatever part we examine. These filaments are flat and composed of four elementary fibres, arranged in nearly the same level, whence they appear like a ribbon. They are also formed of globules, as usual, and are curious, as the two external are most apparent. The middle range is observed occasionally, doubtless, because the pressure it experiences causes the line traced by the globules of which it is composed to disappear. The number of these secondary nervous fibres is yery great, as is seen by the following calculation, even when the results of experiments are not strictly regarded. Let us suppose that each nervous fibre occupies one thirtieth of a square millimetre of a section of a nerve, we have 90,000 for each square millimeter. But we know that the secondary nervous fibres include four elementary fibres. We should then find 22,500 in the same space, or about 16,000 in a cylindrical nerve of the diameter of a millimeter. See their Mémoire sur les phenom. qui accomp. la contract, de la fib. musc., in the Journ. de Physiologie Experimentale, vol. iii. 1823, p. 301. — F. T.*

  • In regard to the composition of the nerves, M. Raspail, from recent microscopical observations, asserts, “ that if a filament from a nervous trunk be examined by

the microscope, the trunk is seen to consist only of an agglutination of cylinders, the 50th part of a millimeter in diameter.” Fontana has proved that these cylinders are composed of a smooth and transparent membrane, containing within “ a glutinous, transparent, and elastic matter that does not dissolve in the water in which the cylinders float.” Having pressed out this matter between two glasses, he caused it to return again by diminishing the pressure. M. Raspail considers each of these cylinders as a cellule which has grown only in length. It incloses a true cellular tissue, imbued with a homogeneous and fatty substance. It has no longitudinal cavity, and its growth extends itself from the encephalon to its extreme ramifications. Am. Med. Jour., Nov. 1828, from the Répertoire d' Anatomie, &c.


OF THE NERVOUS SYSTEM IN THE NORMAL STATE, 159

instance, are always finer than those of the superior, although the nerves of the latter are larger than those of the former. The laryngÅ“al nerve appears as one fasciculus, on which are numerous furrows, which indicate the smaller cords, and it is surrounded externally only by a tissue composed of fine filaments. In some nerves, as the median nerve and the sciatic nerve, the size of all the cords is nearly the same. In others we see the large cords alternating with those which are very small. The anastomotic structure, so apparent in most of the nerves, is not observed in the optic nerve which is composed of straight separate cords, which proceed one at the side of another ; these cords do not divide in turn into others which are smaller, so that we may consider them filaments as well as fascicuh.

In regard to figure, the nerves are generally similar in then round form ; nevertheless, the olfactory ditiers from all others, as its shape is triangular.

Most nerves resemble long trunks, which give off branches along their course, and gradually divide into smaller trunks. The cords and fasciculi consequently are united here. Another arrangement is seen in the nerves of the abdomen, where the fasciculi and cords are separated from each other ; so that the trunks which are formed, when compared with their branches, are not very thick. This difference must be ascribed partly to the difference in the form of the regions to which the nerves proceed, since the trunks of the extremities are the longest of all, and those of the head and trunk are much shorter ; and it must doubtless be ascribed also partly to the general law, which is, that the organisms and organs of an inferior character are, as a whole, less centrahzed than the organs and organisms of a superior character.

§ 152. The large or small collections of fibres of which the nerves are composed, do not remain united ; but the nerves ramify in their course, as their fibrous fasciculi separate. The trunks divide into branches, and these into twigs, &c. The branches are generally given off at acute angles. But the cords and filaments which unite to form a secondary division, are , always separated within the trunks much higher than they seem to be when we examine their surfaces only. In this arrangement the nervous and vascular systems differ greatly. It is not strictly correct to say, that the structure of the nerves differs from the arrangement of the vessels, because the cords and filaments which constitute a trunk or a branch of a nerve partially retrograde, as there is something analogous in the arrangement of the branches and ramuscules of the vessels. But the nerves differ from the vessels because their trunks sometimes run a long space without dividing, while the vessels ramify every where and at short intervals, except in a few instances, as the spermatic vessels, which in fact prove nothing, since this arrangement exists because, at a certain period of life, the vessel is inclosed in a small space.

§ 153. The fibrous and anastomotic structure is seen not only within the nerves, but is apparent also at their origin and in their course. Many nerves anastomose differently together.


160


GENERAL ANAl'OAlV.


There are three kinds of anastomosis : 1st, anastomosis, properly so called, or union in a web, {ansa) ; 2d, the plexus ; and 3dly, the ganglion.

Anastomosis is formed by isolated branches of different nerves, which have nearly the same size. In this mamrer, for instance, the ulnar and the median nerves unite in the hand ; the spinal rïerves, shortly after, leaving the vertebral canal, the different branches of the fifth pair, the branches of this nerve, with the facial and cervical nerves. In this manner also the ansa', are formed around the vessel. Anastomosis occurs ;

1st. Between the different branches of the same nerve, as is seen in the fifth pair, those of the facial, laryngœal, and intercostal nerves.

2d. Between two branches of different nerves, situated, however on the same side, as between two spinal nerves, or between the branches of the spinal and the interpostal nerves.

3d. Between two branches of synonymous nerves on each side, as the superficial nerves of the fifth and seventh pairs, and the nerves of the neck.

§ 154. The plexus(l) is, properly speaking, only an anastomosis between the different cords of the same or of different nerves. The cords divide into very mmute branches, and the filaments which come fromthis division give rise to very numerous anastomoses between different nerves ; so that the new nerves, which come from the plexus, are formed of filaments derived from many different trunks. The pneumogastric nerve, before it enters the lungs, is an instance of a plexus formed by different cords, coming from the same nerve. The plexuses formed from different nerves occur in the nerves of the upper and lower extremities particularly.

One cannot admit the difference between the plexus and anastomosis, mentioned by Bichat, when comparing the communication between the filaments of the facial nerve; and of the fifth pair with that between the spinal nerves, by saying, that in the former there is an intimate mixture, a perfect fusion or identity, while there is only a simple propinquity, a simple juxtaposition in the second ; for there is as much fusion and mixture in both ; but in the latter, the branches which unite are smaller and more numerous.

§ 155. The structure of the ganglions is more complicated than that' of the plexus, and their destination is probably different. 'Their existence seems to be more independent than the plexuses ; they appear to be distinct bodies, much larger than the nerves with which they are united, while the plexuses are simple communications which intimately connect adjacent nerves, but do not increase their substance.

The ganglions(2) have no general and regular form ; in different persons they vary exceedingly in size, form, attachment, and even inti) Scarpa, Dc nanorum gavgLiis ct plcxubus, 1779.

(2) Haase, De gaTigliis nervorum, Leipsic, 1772. — Kwiatowsky, 'Fhescs anal, phys. dc nervorum decussalîone et gangliis, Königsberg-, 1784. — Weber, De systemaie nerveo organico, Leipsic, 1-817. — Wuizer, Dc corporis humani ga7igliorumJ'abric& alqucusu, Berlin, 1817.


OP THE NERVOUS SYSTEM IN THE NORMAL STATE.


161


existence, since large ganglions are sometimes entirely deficient. Most of them, however, are rounded, a little flattened, smooth on the surface, situated very deeply, and sunrounded with an abundance of cellular tissue. They are somewhat hard, and of ordinary color. When we open them, Ave see they are homogeneous masses, having no determinate structure. In all then quahties they singularly resemble the lymphatic glands. The substance of which they are composed is ahvays closely surrounded Avith a peculiar thin membrane formed of mucous tissue, and very abundant in vessels, over Avhich there is either a loose cellular tissue, or a fibrous capsule, a continuation of the dura mater spinahs. Nerves arise from the ganglions.

When the nervous ganglions are macerated, they can be resolved into two substances, viz.into conAmluted filaments, Avhich are continuous Avith the nerves attached to the ganglions, and a grayish red, gela tmous,saltis mass, Avliich fills the spaces betAveen the filaments, and also envelopes them. According to Scarpa(l) the latter substance is oily, and e\'en pure fat in gross people. Bichat(2) Avas mistaken hr sajdng that fat is never formed in the ganglions.

lire substance of the nervous ganglions is very vascular.

§ 156. The ganglions may be divided into simple and compound. The former are developihents of the filaments of one nerve only, and communicate Avith no other. The compound, on the contrary, are the central and connecting points of several nerves. They differ too from each other m more than one respect.

§ 157. The form and situations of the simple ganglions are constant. They are never deficient, and are found near the origins of the spinal nerves, and belong to their posterior roots. Their envelope and substance is firmer than those of the compound ganglions. Then external capsule continues Avith the dura mater spinalis, and the internal Avith the spinal portion of the pia mater. Although the filaments of these ganghons ramify, and anastomose very extensively, yet they have all the same longitudinal direction. Nerves arise from them only in the two opposite points, viz. from the inside arises that portion of the posterior root of the nerve Avliich is betAveen the ganghon and the spinal marroAV, and from the outside, the external rrerve^Avhick soon connects itself Avith the a,nterior root. (§ 170.)

§158. The compound ganglions exist in every part of the body, but are found principally in the thoracic and abdominal carities, more particularly in the latter. They are softer than the simple ganghons ; theh external envelope is formed by the surrounding cellular tissue. They vary in form, situation, and number. Their constituent fibres do not extend from one extremity to the other, but proceed in ah directions. Finally, nerves emerge not only from their two extrcrHities, but from vmrious points of their surface. The filaments neor come from the points where other nerves enter ; hence these same filaments are never intercepted at very acute angles.

(1) Loc. cit. p. 16. •

(2) General Anatomy, vol. i. p. 259. 21


Vol. I.


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§ 159. The fibrous structure and the intercrossing of the nerves are also found in the brain and spinal marrow ; but here they are less evident than in the nerves. At first, the brain and spinal marrow seem formed only of a soft, pulpy, and homogeneous mass ; but the fibrous structure should not be denied on account of this appearance, as has been done by several anatomists.(l)

We have no need of mechanical or chemical agents to observe in many places distinct fibres, especially in those brains which are firmer than usual. Thus they are seen in the corpora pyramidalia of the medulla oblongata, the crura cerebri, the corpora striata, the corpus callosum, the tuber annulare, the commissures generally, and in the fornix. We have even distinguished them on cutting into the mass of the hemispheres. But those who admit their existence in several parts of the encephalon, say it is not certain that the structure of the whole organ is fibrous, or at least they allow it only in certain cases. (2)

Others, who admit the existence of these fibres after death, regard them as produced by the coagulation of the cerebral substance, which they consider pulpous during life ;(3) consequently these two opinions are similar. Malpighi was the first to demonstrate the fibrous structure of the brain, and to describe in what manner its fibres come from the spinal marrow. But the principal writers on this part of anatomy are Gall and Reil ; the latter, especially, has rendered a very important service to science in making known the structure of the spinal marrow,(4) which, before his time, had been regarded as a shapeless, pulpy mass, even by those who admitted the fibrous structure of the brain.

Those who admit the fibrous structure of the brain, differ in opinion whether this structure be peculiar to the medulkry substance, or whether the cortical substance also be fibrous.

Those who admit fibres in the medullary substance, deny that they exist in the cortical ; as Malpighi, Haller, and SÅ“mmening. The cortical substance, however, is truly fibrous. In dissecting some very firm brains, we have often observed, not only the phenomenon remarked by St,enson(5) and Vicq d'Azyr,(6) viz. that the delicate fibres of the medullary substance may be followed into the cortical portion, but also that the latter is evidently fibrous in its structure.

The fibrous structure of the brain is demonstrated by another circumstance ; that the fibres are always arranged in the same manner, however various are the means used to demonstrate them.

§ 160. The spinal marrow makes the transition from the nerves to the brain, since it is, like the latter, inclosed in a bony case, enveloped by the same membranes, communicates directly with it, and

(1) See Bichat, Ano,t. dcscrip. vol. iii. p. 96., where he g'ocs so far as to ascribe the transverse fibres of the coitus callosum to a slig-ht laceration by the knife.

(2) Haller, De part. vol. iii. ç. 48.— Scemmei ring. Nervenlehre, p. 29.

(3) Ackermann, Lieber die GaU'sche Schädellehre, § 6.

(4) De cerebro, Amsterdam, 1669, p. 8-10.

(5) Disc, sur I'anat. du cerveau, Paris, 1669.

(6) Mém. de Vac. des sc, 1781. p. 511.


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first view has a soft and pulpy appearance ; but in texture it resembles the nerves. It is closely surrounded with a membrane formed of mucous tissue and of vessels, which resembles the neurilemma, but is called the pia mater, on account of its intimate union with it, or the vascular membrane, from its numerous vessels. A simple prolongation is detached from the centre of the internal face of the anterior part of this membrane, which goes inward and backward, and penetrates to the centre of the spinal marrow. Numerous small channels arise from each side of this prolongation, which pass through the whole spinal marrow, anastomose frequently together, and are visible, especially when the medullary substance has been destroyed by an alkaline solution. This structure is also seen when the spinal marrow is hardened by immersion in an acid, for it is then divided into numerous longitudinal layers, formed in their turn of very fine cords. Sometimes it is observed in the spinal marrow in its natural state, when its two portions are gently separated ; and it may be distinguished also on the surface of this organ if it be naturally firm, and its pia mater be removed. The channels are smaller in the gray than in the medullary substance, and are limited suddenly by it.

The internal structure of the spinal marrow is then more analogous to the nerves, although it is softer and its fibres are less apparent.(l)

§ 161. The spinal marrow is composed of two lateral parts, which are separted from each other before, by the prolongation of the pia mater above mentioned. Towards the upper part of this organ, near where it enters the skull, its cords divide into several fascicuh, which cross obliquely, so that those from the right side pass to the left, and vice versâ. At the same time, these are enlarged by the addition of several masses of gray substance. On the sides are detached the crura cerebelli, or corpora restiformia, which develope and give rise to the cerebellum. Before and above are perceived the pyramidal bodies, {corpora pyramidalia,) two oblong eminences placed near each other, on the under face of the upper extremity of the spinal marrow. These pass over a large projection formed of transverse fibres of cortical and medullary substance called the pons varohi, or annular protuberance, {nodus cerebri,) and penetrate the inferior face of the brain, where their fibrous structure becomes apparent by the separation of their medullary substance, in the interstices of which the gray substance extends. Being now much enlarged and divergent, they pass before the pons varolii, and produce the peduncles of the brain, {crura cerebri.) These pass below and across the two masses of gray substance, situated one at the side of the other, called the thalami optici, and before which are formed the corpora striata; after this, their fibres, becoming very apparent, unfold in all directions in the cerebral hemispheres, of which they form the principal part, and extend circularly ; this radiation of fibres from the gray substance is called, by Reil, the corona radiata {stabkranzes).{2)

(1) SÅ“mmerring-, Nervenlehre, p. 62-63.

(2) Reil, Archiv., &c. vol. ix. P. 1. p. 159.


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§ 162. The two lateral portions of the spinal marrow and of the encephalon are not only placed close to each other, but are attached by medullary fibres, and gray substance. The places where they are connected may be termed by the general name of commissures. These commissures are every where narrower than the parts which they unite. If examined attentively, they can be traced in each part much farther than one would suppose at first view. As the fibres described in the preceding paragraph are longitudinal, while those, of the commissures are, on the contrary, oblique, Gall(l) considers them as forming a peculiar fibrous apparatus, and admits both in the cerebrum and in the cerebellum, an order of diverging, and one of converging fibres. These two orders have been more physiologically termed the first, the apparatus of formation, the second, the apparatus of union. They are also naiued fronr the parts they concur to form ; the first, the system of the cerebral peduncles ; the other, the system of the corpus callosum. The fibres of these apparatuses differ, not only in their direction, but in their origin, position, and consistence. In fact, while the diverging fibres terminate at the external surface of the encephalon in the gray substance, the recurrent fibres arise from the graysubstance and proceed on the median line, where they unite by commissures of greater or less extent. We cannot consider these unions themselves as origins of the recurrent fibres ; for it is a general law, that the medullary substance aidses from the gray substance, and the commissures extend some distance beyond the two cerebral hemispheres. The fibres of this system are placed between those of the diverging system, and consequently much more internally. They are much softer and finer than the latter. They form distinct layers, which envelope the cerebral ventricles. In admitting this second system which arises from the gray substance deposited on the surface of the encephalon, we explain how the two parts of the organ inclose more of the nervous mass than the corpora striata, so that they appear only as an appendage or appurtenance of these parts.

We cannot determine with precision how the two systems unite. Even Gall admits that we cannot ascertain whether the fibres of the diverging mass are reflected in the gray substance, and change their direction, and thus produce a new recurrent nervous system, or if the latter be really a separate body, which does not arise from the former. Reil, who does not appear to admit a single system of commissures connected in all parts, since he describes the structure of the corpus callosum separately from that of the anterior commissure of the brain, and no where informs us that their expansions are connected, Reil, we say, thinks the two systems are not in every part united in the same manner. He only states generally in regard to the union of the radiating fibres of the anterior commissure with those of the cerebral peduncles, that they form a whole, but he believes the modes of union be

(1) Gall, On the anatomy of the nervoys system, Paris, 1809. — Ibid. On the anatomy and physiology of the nervous system, Paris, 1810.


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tween the radiations of the corpus callosum and that of the cerebral peduncles are numerous. In fact, we find between them and forward, a medullary substance less evidently fibrous, which unites them. Farther back, the two systems anastomose ; and still farther, their fibres reciprocally penetrate each other, and intercross several times, forming a dehcate suture ; finally, the most posterior part of the corpus callosum passes above the system of the cerebral peduncles without uniting to it, and gives origin to two separate masses, which may be enthely detached from each other.(l)

§ 163. The structure of the brain dilfers from that of the nerves principally in two respects ; 1st, its constituent fibres mostly form layers ; 2d, we find no neurilemma withm it. Its fibres are loose and the surface of the brain is covered only with a capsule analogous to the neurilemma, which, as in the spinal marrow, is called the pia mater. The neurileimnatic tubes do not exist, even in those parts which, from their form, are usually considered as nerves.; as that part of the optic nerve situated behind the place of crossing, and the olfactory nerves. Thus they consider the olfactory nerves as making a part of the brain itself, and very properly regard their branches alone as constituting so many distinct olfactory nerves. Besides the absence of neurilemma, the form of the nerve, its graymass and the swelling of its round extremity, which resembles a ganghon, are so many chcumstances in favor of this opinion. The same remarks apply to the inner part of the optic nerve, which would then arise only at the place of crossing.

The aiTangement of the pia mater, however, and its relations to the cerebral substance also establish an analogy between it and the neurilemma. On one hand, the external surface of the brain is folded, at least partially, in certain animals ; and every where in man, and in most mammaha, has circumvolutions igyri) and fuiTows (sulci) situated between them, by which the pia mater penetrates to the internal surface of the brain, into the ventricles, where the c/i&rofdproces.ses, (processus choroidei) form, and numerous vessels eirter, especially in certain tmiform places, into the internal part, and may there be recognized on examination, not only by red points in consequence of the blood which flows out when they are cut, but may even for a short distance be drawn out freely from the soft parts. On the other hand, several parts of the brain resemble the nerves, both externally and internally : such as, for histance, the anterior commissure which is surrounded by a cellular sheath furnished by the pia mater of the ventricles ; this sheath accompanies it in its course across the thalami optici and is changed, hke the neurilemma, mto a delicate cellular tissue, and disappears only at that part where the extremities of the commissure expand into a radiated tissue. (2) Perhaps, then, the struc (1) The recurrent fibres of the brain are not admitted by Tiedemann, who considers the cerebral commissures and the corpus callosum merely as prolongations of the cerebral peduncles. (See his Anatomy of the Brain, p. 266.)

(2) Reil, Archiv, vol. xi. P. i. p. 91.


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lure of the brain is every where the same as that of the nerves, but the softness and fineness of the mucous tissue prevents its demonstration.

§ 164. From the above remarks it follows, that the brain and spinal marrow are formed of fibrous fasciculi differently intermixed ; that these fasciculi are perceived more easily in the medullary than in the gray substance, and that their connections are more or less evident. It follows, then, that the nervous mass contained in the shull and vertebral canal is formed, essentially, after the same type as that formed in the rest of the body, and that the principal difference behveen the two masses is, that thefrst is accumidaied in one jyart, ivhile the second is more diffused.

§ 165. The gray substance does not form, like the medullary substance, a continuous system. According to several anatomists(l) the neurilemma supplies the nerves with a gray substance, because these are not so white as the cerebral substance, and become more voluminous as they leave their centre. But these two circumstances are not sufficient to establish the opinion in favor of which they are adduced, although this opinion is probable to a certain extent, as it increases the analogy between the brain and nerves. That it should be more than probable, it is requisite that the pia mater should no where possess the direct power of producing the medullary substance, but it really does possess it in several points of the encephalon, and in all the spinal marrow. So little does the gray substance represent in the brain a conneeted whole. The gray substance, it is true, forms an uninterrupted layer over the whole surface of the cerebral organ, but it does not communicate with the nerves of the same substance within this viscus, nor can we demonstrate an uninterrupted communication between these latter.(2) Some anatomists admit, also, a sort of communication dependent, 1st, on the vessels, as the cortical substance is entirely vascular ; 2d, on the communication between the internal portions of the thalami optici with the corpora striata, the tubercula quadrigemina with the other parts of the encephalon, and the medulla oblongata with the pons varolii ;(3) but the truth is, that a layer of medullary substance exists every where between the gray substance of the thalami optici and that of the corpus striatum, (4) and that the gray substance of the pons varolii and of the olivary bodies does not communicate with the distant masses of this same substance. (5)

The gray substance diffused in the body by the ganglions, is likewise insulated. The mass of this substance within the brain, and generally in all the central parts evidently corresponds to that which ex (1) Battle, Exerc. de prine. anim., p. 156.

(2) Munro, On the nervous system, chap. 10, § 25.

(3) Ludwig, De cinerea cerebri substantiä, Leipsic, 1778, p. 11, § 2.

(4) Wenzel, loc. cit. chap. 6.

(5) Vicq-d'Azyr, loc. cit., an. 1781, p. 507.


OF THE NERVOUS SYSTEM IN THE NORMAL STATE.


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ists in the ganglions. (1) When man is fully developed, the quantity of the medullary substance is much greater than that of the cortical.

§ 166. The inner ends of the nerves communicate with the central parts of the nervous system. The fasciculi which form them, there separate more or less distinctly, proceed without communicating together, and enter the cerebral substance ; but we camiot distinctly perceive where the fibres of the two unite.

Two questions arise as respects the origins of the nerves. With what substance of the central part are they connected 1 Do the origins of the synonymous nerves communicate, or do they arise from sides opposite to where they are distributed, so as to intercross ?

§ 167. In regard to the first point, the most general opinion is, that the nerves arise fi'om the medullary substance ; that they radiate from it and are prolongations of it. (2) It has even been conjectured that in the spinal marrow this substance is placed externally, so that the nerves which come from it pass over less space, and are not obliged to penetrate through the gray substance. (3 ) Nevertheless, when closely examined, all the nerves are seen to communicate more or less evidently with the gray substance. Vicq d'Azyr had ascertained this fact, as he says that the gray substance is generally accumulated near the origins of the nerves. (4) Gall has added his testimony in favor of it, and we are satisfied from our observations that he is perfectly correct.

This fact is incontrovertible in regard to insects, worms, and fishes, where the nerves arise by several roots from the mass of gray substance. It is evident, also, in some nerves of the superior animals, and of man, for instance, in the olfactory and optic nerves. It is more difficult to prove it in regard to the other nerves, which, at first view, seem comiected only with the medullary substance ; but we must carefully distinguish the place where the nerve detaches itself from the central mass, from that where it arises. (5) Although in the first of those two points, which is external to the central part, most of the nerves communicate with the medullary substance only, and several, as almost all of the cerebral nerves are so feebly attached to it, that they may be easily separated from it, whence we might infer they arise from it ; we can, however, follow them farther, and at a certain depth, sometimes their bundles unite in a cord which communicates with the gray substances, as takes place for instance, in the fifth pair' ; sometimes their filaments come from this same substance separately, as is the case with all the spinal nerves.

(1) This is intended for Haller, who says expressly; In homine et quadrupedibus, quce mihi innotuerunt, in nervis ipsis ejusmodi noduli unice reperiuntur, neque in cerebro unquam aut in spinali medulla. (De part. corp. hum. fab. vol. viii. p. 322.)

(2) Haller, De part., vol. viii. p. 319. Frincipium nervorum communi sensu in medulla est encephali et spinalis medulla:.

(3) Martin, De nervis corp. num., Halle, 1781, p. 27.

(4) hoc. cit, p. 508.

(5) By origins of the nerves, we commonly understand that portion between the place where they arise from the central mass and that where they emerge from the skull. But this term is too inconvenient to be long retained.


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Although in man and the superior animals, all the parts of the spinal marrow, from whence nerves arise, are not enlarged by the accumulation of the gray substance, as Gall pretends, yet we cannot deny but that this substance exists in greater quantity at the origins of the large nerves. Hence its greater volume at the origin of the nerves which go to the extremities.

§ 168. But although we should seek the origin of the nerves beyond the surface of the central mass, we have no right to believe it deeper than we can trace it, and to consider all the nerves as arising from a single point of small extent ; an opirrion mairrtairied by those who are disposed to consider the medulla oblongata as this corrrmon origin.

§ 169. Do the nerves arise from the same side of the body as that to which they are distributed ? Do the synon-ymous nerves unite or cross each other ? or do we find both urrion and crossing ? All these problenrs have been resolved, sometimes rregatively and sometimes affirmatively. Throwing out of view the fact that all observations have rrot been made with the sanre exactness, the difference of opinion in this respect depends on this, that the arrangement of the parts is not the same in all arrimais. The interlacing of the rrervous fibres has been supposed, from the paralysis of one side of the body, when the opposite side has been injured. ( 1 ) But we learn from dissections, both in the normal and abnormal states, that these observations and experiments demonstrate orrly the crossing of the spinal marrow at the point mentioned above, (§ 161,) and do not prove that all the nerves arise from the half of the brairr or spinal marrow opposite to that side of the body in which they are distributed. Although we have often followed the spinal rrerves into the gray substance, we have never observed a single filament passing to the side opposite. Injuries of the central portion are not followed by a paralysis of the opposite side of the body, when they affect a part above that where the intercrossing, of which we have spoken, takes place. This paralysis of the opposite side occurs when the medulla oblongata is injured,(2) but not when the parts below are affected ; for then it supervenes on the same side as that where the section of one half of the spinal marrow has been made. Galen was acquainted with this difference in the consequences of the injuries of the brain and spinal marrow. (3) Even when one half of the spinal marrow is cut near its upper part, paralysis takes place only on the corresponding side, as is proved by recent experiments. (4)

(1) Hippocrates, Epid., Book vii. § 1. — Valsalva, in Morgag'ni, Ep. vol. xii. p. 14. — Prochaska, Obs. path, in Opp., Vienna, 1800, vol. ii. p. 298-320.

(2) Yelloly, A case of tumor in the brain ^ with remarks on the propagation of nervous influence; in the Med. chirurg. trans. vol. i. xvi. p. 181-222. A tunaor as large as a nut on the left side of the pons varolii and of the left pyramid, produced a paralysis of the right side.

(3) De anat. administr. vol. viii. p. 5, 6.

(4) Yelloly, loc. ciL, p. 197.


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No interlacing, either in the brain or spinal marrow, can be demonstrated, except that which exists in the place indicated above. Observations and experiments, from which it has been concluded that fibres cross each other principally in the corpora striata(l) prove nothing. Besides the proposition contradicts itself, since the corpora striata are not connected with each other ; nor does the anterior commissure, which passes through them, communicate either with their proper substance, or with the fibres which enter them. From these observa-lions we can only observe, that the fibres cross below the corpora striata, as we have proved above.

Still a partial communication takes place between some of the nerves, as their external filaments arise from one side, and their internal from the side opposite. This anangement however has been observed only in the optic nerve.

Nor can we demonstrate that the origins of all the nerves unite on the median fine, although this union is sometimes observed between the corresponcUng nerves of the foiuth pair, and the auditory nerves. Probably this is not rare, especially in the spinal nerves.

§ 170. The origins of all the nerves are similar in one respect, that the fasciculi which form them separate from each other in those places (§ 147). But the spinal and cerebral nerves differ constantly from each other in their mode of origin from the central mass.

In fact the cerebral nerves arise by a single root, while the spinal nerves have two, a posterior and an anterior, corresponding to the anterior and posterior faces of the spinal marrow. Nevertheless, we see that the nerves of the brain (commencing at the fifth cerebral nerve) resemble those of the spinal marrow by the division of their fasciculi into two parts. The posterior roots are always larger than the anterior, and usually arise nearer the centre of the spinal maiTow : but their fascicuh are fewer and less evidently fibrous, single, and do not ramify, while the anterior come from the medulla by numerous rami-' fications. The two series of the anterior and posterior roots are separated by a prolongation of the tunica arachnoidea, called the Ugamen ium deiiticïdatum, vv'hich goes from the lateral face of the medulla to

^ ® i.

the corresponding part of the internal face of the dura mater.

The fascicuh of each nervous root are also remote from each other until they leave the dura mater spinalis, and are connected only by a looser mucous tissue. But arrived at the dura mater, they reunite, and each root emerges by a single foramen, formed by tliis membrane. The foramina of the anterior and posterior loots are near each other, but always separate, and the roots unite in a single nerve only after traversing the dura mater.

On the contrary, the fasciculi which form the cerebral nerves come from the diua mater by a single opening, although at the moment they

(1) L. Ca\âa.m, Esperietize ed. osservaz. dirctte a determinare quoi sia il luogo principale del cervello, in cui, pin di altrove le fibre medollari dello stesso viscera si incrocicchiano ; in Mem. di Padova, vol. i. p. 1-16.

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GENERAL ANATOMY.


arrive at it they are not intimately united, as is seen particularly in the posterior nerves.

The direction of the origims of all the nerves is not the same. The cerebral and spinal nerves are totally different in this respect. The nerves of the encephalon are all directed forward, those of the spinal marrow downward, except the first two, the superior fasciculi of which descend, while the inferior ascend.

The cerebral nerves generally proceed much more directly forward, and the spinal form acute angles at the base, which are more acute as the first arise farther forward, and the second farther behind. The middle pairs, the posterior nerves of the encephalon, and the upper spinal nerves, have a more oblique direction.

We also find, that the filaments of several pairs of nerves communicate within the dura mater, as is seen especially in the upper spinal nerves, and also between the fourth and fifth pairs of the cerebral nerves.

The posterior root of each spinal nerve, shortly after passing through the dura mater, becomes a simple, oblong, rounded ganglion, (§ 157,) with which the anterior root does not communicate,(l) although, as Gall very justly remarks, we sometimes see, especially in the neck, the anterior roots forming thick reddish plexuses, which may be considered as ganglionary bodies.

In many cerebral nerves, either in their passage across the dura mater, or at some distance from this point, we see analogous bodies, which are formed however by all the nervous fasciculi.

§ 171. The nerves gradually enlarge in their course. In fact they always ramify ; and the trunks which arise from the encephalon and spinal marrow divide into branches, twigs, and filaments. These are given off almost always at acute angles, and rarely at right or obtuse angles. But if we imagine all the branches reunited, we shall have a cone, the summit of which c.orresponds to the origin of the nerve, and the base to its periphery. This is a general law. The nerves which do not give off branches in their course, as the optic nerves, the auditory, and also the olfactory nerve, (if the portion of the nervous system generally so called, be a real nerve,) are not every where equal in size, but sometimes even become thicker, as is seen in the last two especially.

(1) Scarpa is g-enerally reg'arded as having' discovered that the gang'lions of the spinal nerves are formed onlyby their posterior root.' The honor of this discovery is however ascribed to Monroe by Nicolai {De meduUâ spin. av. Hal. 1811, p. 28); but wronffly, since Prochaska states, in his treatise on the nerves, (1778, p. 139,) “ Funiculi posterioris principii {nervorum, spinalium) soli in ganglium spinale intumescunt ; anterioris vero principii funiculi ganglia illi ope cellulosæ adhærentes solummodo et prÅ“tereundo cum posterioribus ex ganglio egressis primo conjuguntur," &c. Scarpa's work appeared in 1779, the original of Monroe's in 1783; but Haase {De gangliis nervor. Lcips. 1772, p. 87) says: “ Sed hÅ“c, {radix nervorum spinalium anteriori,) non tota in ganglion inserebatur, sed paucis tantum succulis in ganglion immisis, major hujus radiais pars ganglion quasi præterihat, ut nonnisi contextu eelluloso ganglio leviter agglutinata per foramen vertebrale. Thus the hoBor of this discovery belongs to a German.


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The three branches of the fifth pair are evidently larger than its trunk, &c. Some branches also are arranged in the same manner, as the nerves of the lips and the cord of the tympanum. This law, however, does not depend on the large size of the nerves of some organs, as among others of those of the muscles of the eye, for this size depends upon the circumstance, that the nerves of which it treats are very large, proportionally, at their origin.

The central mass also enlarges from the inferior extremity of the spinal marrow to its termination in the skull, where it produces the encephalon.

§ 172. The relations of situation between the nerves and vessels are not every where the same. Some nerves accompany the arteries and veins, and this is most usually the case ; we see it in the crural nerve, in the median nerve, those of the forearm and leg, the intercostal nerve, and those of the abdominal viscera. Others accompany the veins only, as the large cutaneous nerves of the extremities. Many proceed alone, at least for some distance, as the ischiatic, the radial, the ulnar, and the larjmgeal nerves. These differences depend on those in the modes and places of origin of the nerves and vessels ; for 1st, the nerves arise more detached from each other, and more directly from the spmal marrow and the encephalon than do the vessels from the aorta and the vena cava ; 2d, the central parts of both systems are distant from each other, so that the principal rays must pass through a certain space before meeting. Hence why the secondary branches of the nerves iissually accompany the vessels, and why the branches of the nerves and vessels enter the organs ai the same point, while their principal trunks are separated.

§ 173. The terminations of the nerves are not every where the same. The optic nerve differs from all others, as it does not ramify ; when it reaches the eye it forms a homogeneous expansion, called the retina. Some assert that the structure of the retina is fibrous,(l) but the observations on which this opinion is founded are not conclusive.

On the contrary we cannot deny that the fibres of the auditory nerve interlace like a plexus, and terminate in a tlrin expansion. Generally, we cannot discern the terminations of those nerves which penetrate to the interior of the organs, and do not form like the preceding, a particular layer, but seem rather blended with their substance. Nevertheless, the final branches certainly become very soft, and consequently, seem wholly or partially deprived of then envelope, so that the medullary substance appears to predominate at their periphery, as also at their central extremities. This arrangement is very important, not only in an anatomical, but in a physiological point of riew, as it establishes between the two extremities an analogy of structiue, expressed, even in the external form, by the uniform separation of the filaments, while the denudation of the medullary substance, in these two points, attests its importance for the reception of internal or external impressions.


(1) Darwin's Zoonomice, vol. i.


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GENERAI. ANATOINU.


'l'he nerves do not probably ramify so much that they are identified to a certain extent with the substance of the organs, for microscopical observations demonstrate the contrary, even in those organs which are very sensible, as the muscles. The finest nervous filaments are, however, certainly twelve times as large as the smallest muscular fibres, but the latter are compressed against each other so closely that we see them only, and cannot perceive the nervous filaments, or even the branches of the vessels, although both are considerably larger than the muscular fibres.(l) Probably then the extremities of the nerves have an atmosphere by which their influence extends beyond their substance. In this manner we can explain how paits, destitute of nerves and therefore insensible, when diseased, experience very acute sensations.

§ 174. The nervous system is not connected with all the organs, nor does it exist to the same extent in those in which it is found. The parts destitute of nerves are the mucous tissue and its semi-fluid fat, the serous membranes, the bones with their medulla, the cartilages, the fibrous parts, the epidermis and its apjiendages the nails and the hairs, some organs of a peculiar tissue, as the transparent cornea, the crystaline humor, and finally certain parts of systems which receive nerves in others, as all parts of the ovum, notwithstanding the large size of the umbilical arteiies and veins.

Among the organs possessing nerves, the viscera of the chest and abdomen are those which receive the smallest and fewest. As they are formed principally of mucous membranes and of vessels, we may say that the mucous membranes are those parts which possess the fewest nerves.

The vascular system stands a little higher in this respect ; the arterial system possesses more nerves than the venous and lymphatic systems.

The nerves of the muscles are still larger. But the muscles differ greatly in this respect. The nerves of the heart are smaller than those of the voluntary muscles, and thus it makes the transition from the arteries to these organs. Among the voluntary muscles, the nerves of those of the eye are the largest, the others are nearly similar in this respect.

The nerves of the flexor muscles are generally larger and more numerous than those of the extensor muscles.

The organs of sense which must be comsidered as simple appendages of the nervous system, are those in which the most nervous substance is found. Of these the skin receives the smallest nerves : but all its parts are not similar in this respect. Thus the skin of the fingers, of the lips, of the clitoris, and of the penis, possesses more nerves than in other places. The olfactory membrane of the nose, and the envelope of the tongue possess still more. The auditory nerve is Still larger, and the optic nerve the largest of all.

(1) Fontana, lieber, das Nipcrngiff, Rerlin, 1787, § 392.


OF THE NERVOUS SYSTEM IN THE NORMAL STATE,


173


Further, all the organs of the senses, except the skin, receive nerves from different sources. One is the nerve of sense, properly so called, which developes itself to give rise to the sensitive apparatus, the other is another pair, generally the fifth. (1) The tongue by its structure and the arrangement of its nerves, forms the transition from the other organs of sense to the skin ; for it receives branches from several pairs, of which one alone is developed in the organ of taste, and that is not a distinct trunk, but comes from the fifth pair.

§175. The nervous . system is supplied with a considerable quantity of blood. The strictest and most exact calculations estimate the blood which goes to the brain of man(2) one-fifth of that in the whole system. The nerves also in their course receive numerous vessels which are proportionally large. These vessels usually penetrate them almost at right angles. Arrived at their surfaces, they divide into two branches, an ascending and a descending branch, which curve, frequently subdivide, penetrate the tissue of the nerve, and anastomose not oidy with each other, but with the adjacent branches. From the frequency of these anastomoses and the numerous vessels of the nervous system, the circulation can never be interrupted. This arrangement exists in all parts of the system : for each side of the brain receives two arteries which anastomose with each other and with those of the opposite side, and form a circle of vessels. The aiTangement of the vessels is also peculiar in this respect, that the circrdation in them is much retarded. This is strikingly seen in the bram where all the arteries make numerous and very considerable curves. The r^essels of the nerves offer sometliing analogous m then division into two branches, forming together a right angle. All these vessels divide also into very minute branches before penetrating into the substance of the nervous system. However, they do not extend very deeply into this substance, at least the nerves of the medullary part of the brain are not tmged, and hardly change their color, even when other parts become entirely red. (3)

The vessels of the gray substance, both in the brain and ganglions, are more numerous and larger than those of the medullary substance. (§. 141.) Even where the latter is external, vessels pass through it to expand in the gray substance. Those which come to the latter proceed inward, dividing continually until they have attamed the white substance, w'hen they change their direction, follow that of the fibres, and do not give off any more branches.

The arteries and veins in the nervous system have not the same relations of situation as m most other parts. In fact, they do not accompany each other mutually ; so that then trunks come from entirely different parts of the skull and nerves. The arrangement of

(1) On this subject see Treviranus, Observations pour servir de complément ä l'Anatomie comparée et à la Physiologie de l'organe de la vue ; in the Aourn. compl, du Diet, des SC. méd. vol. xvi. p. 331.— F. T.

(2) Haller, De part. corp. hum. fiib. vol. viii. p. 230.

(3) Prochaska, Disg. organ, corp. hum. an.plujs. Vienna, 1812, p. 100-103.


1*74


GENERAL ANATOMY.


the veins is peculiar in this respect, that the branches uirite to the trunks in a direction opposite to that of the course of the blood. They have no valves. This arrangement, with that of the arteries, proves that the blood in the brain circulates slowly and uniformly.

The vessels of the cortical substance are also peculiar in this respect, that the veins are not more numerous than the arteries, as in other organs.(l) Ruysch asserts even that this substance has no veins, and that the passage from the arteries to the veins takes place on its outer surface, in the pia mater. (2)

The existence of absorbent vessels and lymphatic glands within the brain has not as yet been demonstrated. Pathological phenomena, particularly the formation of round tumors in the brains of scrophulous subjects, which have been considered as proving the existence of lymphatic glands, (3) prove nothing ; for these tumors may be wholly new formations, as they are in other parts of the body where similar formations are developed.

§ 176. The nervous system is surrounded with different envelopes, which are not alike every where. The most immediate and essential, and that which seems most intimately connected with the nervous substance, is a membranous layer of mucous tissue, in which the vessels expand before they pass into the nervous substance. This membrane is the pia mater, the neurilemma, the principal modifications of which have already been stated, since its transition from the brain and spinal marrow to the nerves is very evident. A thick layer of mucous tissue is found immediately above it. The structure of this tissue is not fibrous in the nerves ; but it is very strong, and has a silvery lustre. It not only entirely envelopes the nerves in all parts, but also sends prolongations internally, which surround their several cords. Serum and generally fat also are deposited within this cellular layer ; it becomes thinner externally, is continuous with the mucous tissue of the whole body, and unites the nerves with the parts adjacent. The nerves within the skull and vertebral canal are destitute of this external and solid envelope ; but the brain and spinal marrow are there surrounded with two membranes beside the neurilemma. The middle lining is the arachnoid membrane, {tunica aracimoidea,) a thin white membrane, which is destitute of vessels. This membrane, after lining the brain and spinal marrow, sends a hollow prolongation, which extends to the opening of the skull or of the vertebral canal, where it disappears.

The third envelope is the dura mater, which takes the place of the periosteum, at least in the skull ; for it is intimately connected to the internal face of its bones, while it does not adhere to the parietes of the vertebral canal. This membrane belongs to the class of fibrous organs. It generally stops at the opening through which the nerve emerges from the skull or vertebral column, and blends

(1) Vicq-d'Azyr, Mem. de Paris, 1783, p. 510.

(2) 7'hes. anat., vi. no. 73.

(3) Reil, Memor. din., vol. ii. pp. 1. 39.


OF THE NERVOUS SYSTEM IN THE NORMAL STATE.


175


with the periosteum and the external cellular membrane which covers it. The optic nerve alone is an exception to this rule ; since, after leaving the skull, until it is inserted into the globe of the eye, this nerve is surrounded by a thick and firm membrane, resembling the dura mater, and entirely different from the external envelope, which continues uninterruptedly with the fibrous membrane of the eye. The external or cellular tunic of the nerves has some analogy with the dura mater, and the two are united. Still the ancient anatomists were wrong in blending them, and in thence admitting that the nerves are enveloped by the dura mater, an opinion which Haller (1) and Zinn (2) have refuted.

The ganglions have the same envelopes as the nerves with which they are connected. All have an internal cellular capsule, analogous to the neurilemma or to the pia mater, in which their vessels are expanded, and an external envelop which arises in the compound ganglions from the cellular coat of the nerves, with wdrich it is blended ; in the ganglions of the spinal marrow, however, this is the same as the dura mater.

§ 177. The nervous substance possesses to a certain degree the power of extending and contracting. But this power does not exist in all parts of the system in the same degree. The changes of form and volume are every where slow and gradual.

The dropsy of the ventricles of the brain proves the extensibility of the nervous tissue. In this disease the thickness of the brain, which is usually several inches, diminishes to a few lines only, and the whole organ becomes an immense vesicle. Here we may mention the nerves over large tumors, which resemble broad flat bands.

The nervous substance is contractile ; for the nerves which are cut across retract, whether they be, or be not organically connected with the parts to which they go.

Elasticity is also a property of the nervous substance. If the brain be compressed, it rises when this compression ceases ; a nerve when drawn out, lengthens, and when released, returns to its original dimensions.

But the phenomena of extensibility, contractility, and elasticity, do not prove the irritability of the nerves, as Home asserts ;(3) for the contractions observed in experiments on nerves removed from the body or still attached to the organs, prove only the existence of the first three properties, and not that they possess the fourth.

All the parts of the nervous system are not alike in regard to sensibility. Its periphery, comprising the nerves properly so called, is highly sensible, and it is even in this that their function consists. This power undoubtedly resides in the nervous substance, since the neurilemma disappears at the extremities of the nerves, and pain is irot

(1) Prim. tin. xi. 270. Zte yttö., vol. viii. pp. 305, 306.

(2) De l'enveloppe des nerfs, in the Mémoires de Berlin, 1753, p. 130-144.

(3) On the irritability of the nerves, in the Phil. Transact, 1801.


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caused by merely exposing these organs, but they must be compressed or divided.

Opinions differ in regard to the sensibility of the cerebral substances. Some writers, particularly Lorry(l) and Lecat,(2) wholly deny it; others, on the contrary, as Haller, (3) admit it in regard to the deep portions of the encephalon, but refuse it to the cortical substance and even to the superficial layers of the medullary substance ; finally, many assert its non-existence in the deep parts, but admit it in the superficial portions. The last hypothesis seems most probable to us. It belongs to Boerhaave (4) and Caldani.(5)

§ 178. Although we have seen above that the masses of gray substance do not communicate, still the whole nervous system is every where connected, and all its parts communicate with each other in difterent modes. We must now point out the relations between these different parts, that is, we must determine, 1st, what are the relations between the two substances, and the functions performed by each ; 2d, what is the mutual relation of the different parts or the principal sections of the nervous system.

§ 179. The medullary and gray substances have undoubtedly important relations with each other, since they exist in all those animals which have a nervous system ; but it is difficult to determine what these relations are. It is generally thought that the medullary substance is connected with the intellectual faculties more intimately than the cortical substance, the function of which is to nourish the medullary substance, or to secrete a principle which acts in it ;(6) and this because it receives so many vessels. The gray substance is sup' posed to be the matrix of the medullary substance,

1st. Because it is generally diffused. It not only covers all the extremities of the nerves, and forms, for instance, most of the pituitary membrane, the retina, and the fluid in which the extremities of the auditory nerve and the rete mucosum of Malpighi are placed, but also accompanies the nerves in their whole course.

2d. Because we find it in masses wherever the medullary substance exists in greater quantity, and its functions are more important.

But these two circumstances are not sufficient to prove that these are the functions of the cortical substance. It is not proved that the gray sirbstance accompanies the nerves in every part, nor that it surrounds their extremities ; and if it abounds in the parts where the medullary substance is found in excess, it may be designed for an end very different from that assigned to it. The accomplishment of certain vital actions may possibly depend on the simultaneous presence, the union, and reaction, of these two substances. If the hypothesis above mentioned were correct, the cortical substance probably would not become more and more

(1) Mémoire sur les mouv. du cerveau, in Mém. prés., vol. ii. p. 354.

(2) Traité du mouv. musc., iterlin, 1765, p. 289.

(3) Mém. sur les part. sens, et irrit., sect. vi. no. 1, exp. 139-147.

(4) Jmpelumjac. die. Hipp. p- 257.

(5) Mém. sur les part. sens, etirrit., vol. iii. p. 82.

(6) Ludwig, De subslantiâcincrcâ, Leipsic, 1779

OF THE NERVOUS SYSTEBI IN THE NORBIAL STATE.


177


predominant as we descend the animal scale ; its relations with the medullary substance would be every where the same.

We need not explain the progressive increase of the nerves from their centers to then peripheries(l) by supposed additions to this substance, since the gray substance within them is demonstrated by no fact, and it is evident that the medullary substance can enlarge of itself.

The most probable hypothesis is that which considers the gray and white substance as two masses in antithesis with each other, while the difference in their structure and chemical composition is necessary to accomplish the functions of the nervous system.(2)

§ 180. Notwithstanding the undoubted importance of the gray substance, we have no right to think that is more noble than the medullary substance, or that the changes m the mind, corresponding to corporeal changes, take place in it, as Wenzel seems to think(3) when he says, “ Cinerea smgularum cerebri partium substantia videhir prÅ“cipue id esse, quo propriÅ“ cuivis istarum partium sensationes ejjicitmtur and tha tthe medullary substance is merely a simple conductor. Reil comes nearer the truth in stating that the principal organs of the soul are placed around the masses of gray substance within the the brain.(4) Haller had already advanced this theory before him. (-5) He says, “ JVbji ergo in cerebri cortice sensus sedes erit nut plena causa, muscularis motus origo ; eritque utraque in meckdla cerebri et cerebelli."

This opinion is favored by the excess of gray substance in the fetus and the inferior animals.

§ 181. What is the mutual relation of the different parts of the nervous system 'I Do they form so many separate systems merely connected iviih each other ? Or do they all emanate from a central part ? The last opinion has prevailed even in modern times. But the first begins to be geneial, although with several modifications.

It supposes either two opposite nervous systems, or many which co-exist and are independent.

§ 182. The first hypothesis which is defended by the most ingenious anatomists(6) and physiologists, opposes to the system formed by the brain, spinal marrow, and their nerves, that of the great sym (1) Sprengel, Inst, phys., vol. ii. p. 191.

(2) A hydrogen and oxygen antithesis, a gray and a white substance, appear to be essential parts of every nervous tissue. (Reil, Archiv für die Physiologie,

vol. ix. p. 485.)

(3) De penitiori cerebri struct., p. 69, ch.ip. vi.

(4) Archiv für die phys., vol. ix. p. 207.

(5) Elém. Phys. vol. iv. p. 392.

(6) Winslow, Expos, anat., vol. iii. p. 220. — Johnstone, An essay on the use of the ganglions of the nerves, 1771. — Pfeffinger, De structura nervorum, Strasburg, 1783. — Sœmmerring, Ueber das Organ der Seele, Königsberg, 1796, p. 9. — We consider the last (the sympathetic nerve,) as a separate pair of nerves independent of the brain and spinal marrow, wbich is, however, connected with them mediately, but not immediately. — Bichat, Traité de la vie et de la mort., ch. vi. § iv. p. 76. — Reil, Archiv, für die Physiologie, vol. vii. part ii. — Gall, Anatomie et Physiologie du sys^ tème nerveux, 7810 VOL. I.


23


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pathetic or intercostal nerve which expands in the neck and in the cavities of the chest and abdomen, and admits only simple connections between these two systems, which are otherwise independent.

As the first is distidbuted principally to the organs which preserve the relation of the mind with external objects, and are subject to the influence of the will, and the second is expanded in the organs wlrich are onl}^ materially connected \vith external objects, the fii'st is called the nei'vous system of animal life, and the other the net'vous system of organic, vegetative, or automatic life.

According to this theor}^, the ganglions, formed of medullary filaments and of a gray substance, ai'e so many small brains from whence the sympathetic nerve arises. Some of the ganglions which form the centres of this system are situated internally upon or beyond the median line of the body, and others on its edges. The nerves of the organs of circulation, of digestion, of the urinary secretion, and partly, also, those of generation, come from the first, as well as those filaments which unite these inner ganglions with those which are placed oir its edge. The latter extend in a row on each side along the vertebral column. They connect the internal ganglions and the filaments which come from them with the system of animal life, since they unite with the cerebral and spinal nerves by one or many filarnents.

The great sympathetic nerve, on the contrary, is generally considered either as a cerebral nerve, the trunk of which proceeds along both sides of the vertebral column, and unites vrrith the spinal nerves by ganglions, while its branches swell out from space to space to form other ganglions, or as a nerve formed by all the spinal nerves. Against this opiniorr and in favor of the preceding,(l) we may adduce the following arguments :

1st. What is termed the trunk of this nerve is often inten-upted without arry derangement in the organs to which it proceeds. We sometimes find a very distinct interval between two or more ganglions.

2d. Other ganglions, not belonging to the sphere of the sympathetic nerves, are always distinct, and communicate by their branches with the cerebral nerves only.(2)

3d. Its trunk is often divided lengthwise, which never happens in the other nerves.

4th. This nervous trunk becomes evidently thicker in its passage downwards, so that it cannot come from the fifth and sixth pairs of cerebral nerves. Nor have we reason to think that it aiises from any of the spinal nerves, since the branches which spring from the ganglions are larger than those which come from the spinal nerves.

(1) Bichat's General Anatomy, vol. i. p. 250.

(2) Bichat also pounds his opinion on the fact, that in birds the upper cervicéJ gangrlion is constantly distinct, and never communicates with the lower. But Cuvier has demonstrated that this assertion is erroneous. Tiedemann {Zoologie, vol. ii. p. 45-46.) and Emmert (Reil, Archiv, p. 337.) have demonstrated this communication still more circumstantially. 4Ve need not observe that by an impartial comparison of the different passages cited, we may easily judge correctly in respect to the claims of discovery after Cuvier.


OF THE NERVOUS SYSTEM IN THE NORMAL STATE. 179

5th. Its texture is different. It is softer and grayer than the other nerves.

6th. Its external form does not resemble that of the nerves of the system of animal life, being neither constant nor symmetrical.

These arguments prov'e only that the great sympathetic nerve does not arise from the brain or spinal marrow by a single point, and that it is distinguished from the nerves by several peculiarities ; but it does not follow that it forms a system independent of the brain and spinal marrow. Far from it ; recent experiments would lead us to think that if it forms a separate system, of which the ganglions are the centres, while its extremities communicate with the nervous system of animal life, this communication is absolutely essential to the integrity of its functions, since the' motions of the heart, which derives its nerves principally from it, are always arrested when the spinal marrow is destroyed, while only a small portion of this organ is necessary for their continuance.(l)

The manner in which the ganghons placed on the borders of this nerve unite with the spinal nerves, also appears to favor this opinion. The filaments of communication arise principally from the anterior cords of the spinal nerves, which are immediately connected with the spinal marrow, instead of coming from the posterior cords, along which ganghonic enlargements are found. (2)

The opinion with regard to the great sympathetic nerve, when thus modified, is admissible, and thus the ingenious Johnstone has stated it.(3)

§ 183. Gall, (4) instead of admitting this general opposition between the nervous systems of organic and animal life, considers the system of organic life, the nerves of voluntary motion, of the senses, of the proper organs of the intellectual functions at least in perfect animals, as so many distinct and independent systems, which are closely united and connected in their action, but which do not come from each other. The nervous system of the senses and of voluntary motion is, however, composed of the spinal marrow, the medulla oblongata, and the nerves which come from them : they may, and even should, be considered then as one system ; since, with a few exceptions, each nerve is at the same time a nerve of sensation and a nerve of motion. Besides, even when we examine the nervous system of organic life, we do not consider the ganglions and filaments separately, nor can we separate the study of the nerves of perception and of motion from that of the brain. The preceding hypothesis is then more probable than that of Gall.

§ 184. But although it is true that the animal and organic nervous systems differ, the second being subordinate to the first, although the different parts of the nervous system considered as a whole, are united

(1) Legallois, Exp. sur le principe de la vie, Paris, 1812.

(2) Scarpa, Annot. acad, 1. i. § xi. xii.

(3) Loc.cit.p. 80.

(4) Gall, p. 467.


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in many different ways, so that, they arc always in a state of reaction and mutual dependence, we cannot deny but that each part is to a certain extent independent of the rest. Each part of the nervous system preserves itself in virtue of a peculiar activity, and reproduces itself constantly from the blood which flows to it. Hence when a nerve is divided it remains as large below as above the cut.

We sometimes find nerves when there is no trace of a brain or spinal marrow, and the spinal marrow is often perfect, although there is not the least appearance of a brain.(l) Even when the development is jierfect, we have instances where considerable injuries of the brain and spinal marrow do not diminish sensation or the power of motion, especially when they are not. sudden, but slow and gradual. The limbs, when detached from the body, are agitated if their nerves be irritated.

§ 185. Hence some late writers have opposed the opinion of the ancients, that the nerves and even the spinal marrow come from the brain, and it is admitted that these parts do not arise from the encephalon, but are merely connected with it. It is even pretended that the nervous system of organic life is formed before that of the nervous system of animal life. (2)

They appear however to have gone too far on this side ; for, 1st. The history of the development of the nervous system in the animal series, and in the fetuses of the superior mammalia, proves that the central part of the nervous system of animal life in fact exists before its radiations, and before the nervous system of organic life. In several worms we find in the place of a spinal marrow, only a simple cord destitute of filaments. (3) The spinal marrow is the first part which appears in the chicken, so that this organ in some measure appears to be the origin of the whole nervous system. In fact we find the spinal marrow without the brain, (4) but never find the brain without the spinal marrow, neither in animals nor in human monsters. When the nerves are seen without the brain and spinal marrow, these two organs existed previously, or the defect is but partial. Hence why the whole brain may be extirpated. A small portion of the spinal marrow is sufficient to sustain life in that part of the trunk with which it communicates ; but if the whole spinal marrow be destroyed, the phenomena of fife cease. (5)

2d. The ordinary results, even of those experiments which are alledged to prove that the different parts of the nervous system are independent of each other, demonstrate that the nervous activity emanates, at least partially and perhaps entirely, from central parts. A limb, if its nerve be divided, becomes feeble and often wastes. The functions of all these parts cease when the continuity of their nerves

(1) Monroe, On Ihc nervous system, p. 20, 21.

(2) Ackermann, De system, nerveis primordiis, Heidelburg', 1813,.

(3) Cuvier, Anatomie comp. vol. ii. p. 330.

(4) Cuvier, Anatomic comparée, vol. ii. § 339.

(5) Malpighi, loc. cil.

(6) Legallois, loc. cit. p. 32-3-4-131.


OF THE NERVOUS SYSTEM IN THE NORMAL STATE.


181


is interrupted, even when these nerves are connected with them in all their extent. Hence, in order that the nerve should perform its functions, it must communicate with the brain and spinal marrow — a fact from which we deduce at the same time a powerful argument against the opinion that the nerves possess gray substance in every part.

The nerve has then the power of vegetating or of nourishing itself independent of the central part ; but it proceeds from this center, and must communicate with it, to animate the oi'gans to which it goes.

§ 186 . -What is the fnnction(l) of the nervous system? Wliat is the relation between its whole structure, and that of its parts, and this function ?

The function of the nervous system is to produce the actions corresponding to the activity of mind, the phenomena of seiisibility or of intelligence. Consequently, it is the system of sensibility. Hence

(1) See on this subject, Lobstein, Discours sur la prééminence du système nerveux dans l'économie animale et l'importance d'une étude approfondie de ce système, Strasburg, 1821. — Charles Bell, On the nerves — Memoir on the respiratory nerves . — Shaw, Experiments on the nervous system, in the London med. and phys. journal, December, 1822, June, 1823. — See also. Journal de phys. exp., vol. ii. p. 77 ; Archiv, gén. de méd., August, 1823, p. 511. — Desmoulins, Recherches anatomiques et physiologiques sur le système nerveux des poissons ; in the Journ. de phys. exp. vol. ii. p. 348 ; Id. Exposition succincte du développement et des fonctions du système cérébro-spinal, in the Archiv, gén. de méd., June, 1823, p. 223; Id. Exposition succincte du développement et des fonctions des systèmes nerveux latéraux des organes des sens et de ceux des mouvemens dans les animaux vertébrés, same journal, December, 1823, p. 571. — Magendie, Expériences sur les fonctions des racines des nerfs qui naissent de la moelle épinière ; in the Journ. de phys. c.vp., vol. ii. p. -276-366. — Rolando, Exp. sur les fond, du syst. nerv., same journal, vol. iii. p. 95. — Coster, Expériences sur le syst. nerv., publiées en Italie en 1819, et répétées en France eh 1823 ; in the Archiv, gén. de méd., March, 1823, p. 359. — Fodera, Recherches expérim. sur le syst. nerv. ; in the Journ. de phys. exp., vol. iii. p. 191, and in the Journ. compl. du Diet, des sc. méd., vol. xvi. p. 290, vol. xvii. p. 97.. — Tréviranus, Essai d'une détermination du rapport des diff. or g. cérébraux aux. div. manifestations delà vie intellectuelle, same journal, vol. xvii. p. 13. — Id. Sur les organes cérébraux, les nerfs de la vie végétative et sensitive, et leurs connexions naturelles, same journal, vol. xvi. p. 113. — Id. Sur les différences qui existent, relativement à la forme et à la situation du cerveau dans les différentes classes du règne animal, same journal, vol. xvii. p. 216, vol. xviii. p. 235. — Desmoulins, Mémoire sur le défaut d'unité de composition du système nerveux, et sur la concordance de ce défaut avec l'irrégularité des facultés des animaux, same journal, vol. xviii. p. 79. — Wilson Philip, On the influence of galvanism on digestion and respiration, cpc., London — Humboldt, Résultats à expér. faites sur les actions galvaniques, et sur les effets de la section longitudinale et de la ligature des nerfs, in the Archiv, gén. de méd., October, 1823, p. 292. — Breschet, M. Edwards, and Vavasseur, De l'influence du syst. nerv. sur la digestion stomacale, same journal, August, 1823, p. 179. The last three memoirs establish the identity between the eflects of galvanism and certain phenomena dependent on the action of the nervous system. Wilson Philip was the first who attempted to re-establish the action of the stomach suspended by the division of the parvagum nerve, by passing a continual current of galvanism across this organ, which was transmitted by the lower extremity of the divided nerve. Charles Bell's observations on the simple and compound nerves, and those of Magendie on the different functions of the two roots of the spinal nerves, are, with those of W. Philip, the most important additions to the science of Physiology, since the commencement of this century. We must, however, admit that C. Bell's theory was indicated, and oven developed, to a certain extent, in- the different works of Lamarck ; among others, in his Philosophie zoologique. — See also Vavasseur, De l'influence du système nerveux sur la digestion stomacale, Paris, 1823. — Foville and Pinel Grandchamp, Recherches sur le siège spécial des différentes fonctions du système nerveux, Paris, 1823. — Flourens, Recherches e.vpérîmentales sur les fonctioriX et les propriétés du système nerveux dans les animaux vertébrés, Paris, 1824. F. T.


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why a perfectly normal state of this system is indispensable to produce these phenomena normally.

But its different parts have different functions, The function of the nerves is to convey the impressions to their opposite extremities, and thus produce changes in those organs which receive these impressions. These changes depend on the nature of the organs. They are sensations in the central part, and changes of volum e or motions, and modifications of the form in the organs different from the nervous system.

§ 187. The nerves are conductors. This is proved by the following facts;

1st. The propagation of the external or internal impressions ceases, when their continuity or connections with the central part and the organs in general are interrupted. Hence the loss of motion, secretion, and sensation, when the nerve of an organ is cut, or compressed by a ligaor tumor in its course, at its origin, or at its entrance into an organ. Hence the loss of smell when a schirrhous tumor compresses the olfactory nerve ;(1) and deafness in another case, where the auditory nerve was compressed in the same manner ;(2) and squinting in a subject, where the origin of the nerve of the sixth cerebral pair(3) was also compressed by a tumor, blindness in a case of compression of the optic nerve by an aneurism of the carotid artery within the skull ;(4) complete paralysis of the arm by the swelling of the lymphatic ganglions in the axilla, thus forcibly pressing upon the brachial plexus. (5) Hence the derangement and even the complete suspension of digestion, and the loss of voice from tying or dividing the par vagum nerve, which goes to the organs of these functions. (6)

Hence, too, excruciating pain is often cured by dividing the nerves of the diseased part ; and sometimes it ceases for a time, even when those nerves are compressed. Hence, finally, the happy use made of this resource against tic douleureux and similar fixed pains in other parts of the body.

The number of parts, then, which lose their sensibility and motivity,is always much greater in proportion as the nerve is tied or divided near its origin. When the loss of these two powers depends on a ligature or on compression, they reappear when these cease to act.

2d. The propagation of the external or internal impressions continues to take place on one side between the point compressed and the central part, on the other between this same part and the organ to which the nerve goes. When we touch the parts of a limb above the place where its nerve has been cut or tied, a sensation is excited, the intensity of which depends on the manner in which the contact is made, and the degree of force given to it. Motion takes place even in

(1) Loder, De tumore scirrhoso el organo olfactus, Jéna, 1779.

(2) Sandifort, Obs. anat.pathol. lib. i. c. ix. p. 117.

(3) Yelloly, in the Med. chirurg. Irans., vol. i. xvi.

(4) Blane, in the Drans. of a soc.for impr. of med. and chir. knowL, vol. ii. p. 193.

(5) Van-Swieten, Comm, in Boerhaav. Aphor. vol. i. p. 222.

(6) Legallois lias collected all the ancient and modern references to experiments on this subject, (he. cit. p. 1 64.)


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a limb detached from the body, when the nerve is irritated ; although the irritation of the parts of the nerve above this division, of the brain, or the changes which supervene in the encephalon, have no effect on the motion of a hmb, the nerve of which is only tied.

3d. Other things being equal, the degree of sensibility and of motivity of an organ depends on the size of its nerves. Hence the large size of the nerves of the organs of the senses, which probably contributes to render them more susceptible of being affected by certain qualities of bodies, although the stmcture of the organs to which they go, their mode of distribution, and the differences in the internal structure of the nerves themselves, are the principal somces of this faculty. Hence why those muscles of the eye which move continually receive the most and largest nerves. The nerves of the heart are neither so large nor so numerous as those of the other muscles, but they come from ganghons which communicate directly with the spinal marrow, and they have more medullary substance in proportion to the neurilemma, than the other nerves.

4th. The central part of the nervous system experiences no change from internal impressions made on the organs which do not receive nerves. These organs are insensible (p. 79).

§ 188. The external and internal impressions are generally conducted always in the same direction. It rarely or never happens that when we touch a nerve, we produce motions in those muscles, which are suppHed with nervous filaments from the trunk, between the point of contact and the central part. Thus the nervous influence which is to act on the external organs goes directly to the periphery.

§ 189. As the phenomena which result fi'om the conducting power of the nerves are finally reduced to sensation and motion, the nerves have been divided into nerves of motion, nerves of sensation, and mixt nerves. But this classification is valueless ; for although there are some nerves intended exclusively for sensation, (as the olfactory, optic, and auditory nerves,) there are none which are designed simply for motion. Those which go to the muscles have in fact only the power of propagating impressions from thefr periphery inward.

§ 190. The same nerves convey external and internal impressions, since the section of one of these cords destroys both sensation and motion. The divisions of these organs into nerves of sensation and nerves of motion, is then incorrect in this second respect.

On the contrary, the phenomena above mentioned (§ 188) lead us to conjecture, with some probability, that there are in the same nerve, different fibres, some designed to convey impressions inward, and others to carry them externally : at least these phenomena are explained very satisfactory by this hypothesis. In fact, the fibres do not apparently differ in arrangement, but the variation may, however, be so slight as to escape us ; hence we draw no conclusions.

This hypothesis is, besides, more probable than that which supposes that the transmission of impressions internally differs from that of conveying them externally, and that it requires less energy to con

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duct external than internal impressions. The partisans of the last theory found it on the circumstance, that the loss of motivity is observed oftener than that of sensibility. Still the contrary case is not rare ; some physiologists believe, even, that it requires more energy to propagate external impressions. And again, the sensibility almost entirely disappears in raphania, although motivity is but slightly diminished.

Finally, the loss of one of the two faculties, with the continuance of the other, demonstrates neither the existence of nervous fibres differing in their conducting power, nor the necessity of greater energy to propagate either internal or external impressions, since the cause of the loss of sensation and motion unquestionably depends on the abnormal state, not of the conducting nerve, but of the centre to which it extends, or of the organ in which its periphery is expanded.

Still less can we admit, that the conducting power of external and internal impressions resides in different substances, viz. that of internal impressioirs in the medullary substance, and of the former in the neurilemma. All the arguments adduced in support of this improbable hypothesis are easily refuted.(l)

Considering all things, it is probable, 1st, that the conducting power resides in the medullary substance alone, and not in the neurilemma.

2d. That all the fasciculi and all the fibres of the nerves equally fulfill the function of transmitting the external and internal impressions, even as the same muscular fibres contract sometimes in one direction, and sometimes in the opposite.

§ 191. The following facts demonstrate that the nerves possess only the conducting power ; that is, they are only the necessary means of producing intellectual phenomena, in accordance with the impressions transmitted by them to the centre of the nervous system, and that, in man at least, the brain is the only organ in which changes corresponding with the phenomena of intelligence occur.

1st. The only portion of the nerves which is not sensitive, and which loses the power of exciting voluntary motion, is that which is separated from the rest of the nervous system by compression or division.

2d. The intellectual acts remain entire when the communication between the brain and the rest of the nervous system is interrupted, and there is paralysis of all those parts of the body which are situated below the parts injured, as, for instance, in dislocations, or fractures of the cervical vertebræ accompanied by compression of the spinal marrow. (2)


(1) Trev'iranus, On ihe nervous influence andils effects, in Phys. Fragmenta, vol. i. Hanover, 1797, vol. ii. 1799.

(2) Vicq d'Azyr lias seen the paralysis of the extremities and of thesphincters of the anus and bladder, with an insensibility of the whole body, except the head, from an injury of the cervical portion of the spinal marrow. (Kncyc. method. IHéd. Anat. pathoL, p. 2(34.) Ludwig has known loss of motion and sensation in the whole body after a fracture of the fourtli and lifth cervical vertebræ ; the patient continued perfectly sensible lor sixteen days. (Advers. med. prop. vol. iii, p. 507.)


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3d. The intellectual functions are more or less injured by the compression, irritation, destruction, violent concussion of the brain, and by changes in its physical quahties ; by the too great or too little flow of blood to this organ ; in a word, by all anomalies which can exist in it, although the structure of the other parts of the nervous system is perfectlyiiormal.

4th. These lesions disappear when the cause which acts on the brain is removed or when the action of this organ returns to its normal rythm.

5th. The development of the intellectual faculties is parallel with that of the brain, in regard to its mass, form, chemical composition, and distinction of its two substances, both in the fetus and in animals. But we should not forget that the increase of the encephalon in size is not exactly ascertained by comparing the brain and nerves together. The large animals have, 1st, a brain positively larger than the small animals, and sometimes larger than that of man ; 2dly, in many, also, it is larger, in proportion to the body, than in others, without a corresponding development of intellect. On the contrary, there is constantly a direct relation between the development of intelligence and the increase of the brain, when compared to that of the nerves. This relation is no where more favorable than in man.

6th. Even from the sense of effort and fatigue in thinking, which very evidently has its seat in the head,at least in preference to other parts.

7th. The brain, although united to the rest of the nervous system, forms a separate and perfectly distinct organ, which fulfills special functions.

8th. After a painful limb has been amputated, the patient thinks he still feels pains at the stump.

§ 192. Most of these facts, especially the 2d, 3d, 4th, 5th, 6th, and 7th, prove at the same time that, at least in man and the superior animals, the brain is the only central part of the nervous system which cooperates with the phenomena of intelligence, and that the spinal marrow takes no direct part in them.

§ 193. Does the whole brain take part in all acts of mtelhgence, or do certain intellectual phenomena occur in some particular parts ? In one or the other case, is there, or not, some more or less extensive part of the encephalon where the primitive source of all spiritual or corporeal hfe resides, in this respect, that the local or general changes which take place in the brain are reflected in it, and that it is the point of departure of all cerebral influence to the nerves ?

Observation and experiment can alone assist in resolving these questions.

The arguments in favor of the first opinion, are, 1st, that most of the brain may be destroyed without a sensible diminution of the intellectual faculties ; 2d, that the destruction of the same part of the brain does not always necessarily involve that of the same intellectual faculty ; 3d, that the complication of the brain remains the same, while its mass and volume increase in proportion to the development of intelligence.

W e may conclude from this, that the whole cerebral mass acts in all intellectual operations, and that a part of this organ, by increasing its activity, can well replace those which may be destroyed.

VoL. I. 24


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The following are the facts in favor of the second hypothesis :

1st. The difference of the intellectual operations, and of the moral qualities which appear to correspond to the complicated and constant structure of the brain.

2d. The development of certain parts of the brain corresponding with that of certain intellectual faculties, and reciprocally.

The arguments favorable to the first hypothesis may be adduced against the second. But we must remark,

1st. That it is very difficult for two injuries of one and the .same part to be perfectly similar.

2d. That from the symmetry and doubleness of the cerebral parts of the brain, the lesion of one of its two portions may be unattended with inconvenience.

3d. That those parts even which do not exactly correspond may supply them, since we see organs formed very differently, as the skin, the kidneys, the lungs, the intestinal canal, the mammæ, the peritoneum, &c., replace each other.

It is, then, not improbable that the different faculties of the soul have different organs m the brain, even as the different corporeal functions, anl the different acts of one and the same function, are performed in the body by different organs, but it is difficult to assign the seat of these faculties ; we can only say that those of a secondary order reside in the lower and posterior parts of the brain, while the most noble faculties exist in the upper and anterior. In fact,

1st. The inferior parts are found in all vertebrated animals commencing with the lowest in the scale.

2d. They do not differ much in different animals.

3d. As the intellectual faculties perfect themselves in the animal series, and in different individuals of the same species, the cerebral mass increases upward, foiuvard, and on the sides ; the hemispheres enlarge in respect to the inferior parts of the brain, which have a definite outward form, and appear as distinct organs ; and the cerebrum is larger in proportion to the cerebellum.

§ 194. The nervous system is not only the organ of the mind ; it animates also all the other organs, because it probably exists before them, and because the vital energy of these organs is proportional to the size and number of the nerves they receive, and the destruction of their nerves deranges more or less the fulfillment of all their functions. Is there a common source of this vivifying and preservative power of the nervous system, or is it diffused through the whole of it ?

That the periphery of the nervous system takes no part in the preservative influence exerted upon the whole organism, is proved by tlje fact that all the fimbs may be amputated without destroying life. The source of this faculty undoubtedly resides in the central part. But is it diffused through all the central mass, or confined to a particular part 1 The former is not true ; of this we may be convinced by comparing the degree of tenacity of life in those anim'als in which the brain is considerable, and those in which it is small. The difference in this respect must undoubtedly be ascribed to this, that the two conditions


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are directly opposed to each other. Experiments seem to demonstrate that the source of the preservative power, which exerts an influence on the whole organism, resides in the medulla oblongata ; since if this part be injured, life is destroyed sooner than from wounds of any otherpart of the brain or spinal marrow ; and farther, the latter have been found changed, and the vital functions have not been atfected. This part is principally important because the par vagum nerve arises here and goes to the organs of respiration ; for when that is injured, the second condition, which is essential to mamtain life, the chairge of venous into arterial blood in the lungs, no longer takes place, and the vital energies cairnot be produced. Thus, after destroying the medulla oblongata, and even separating the head from the body, if artificial respiration is carried on, the trunk continues to live during a certain period, if the spinal marrow be uninjured, and the vessels are carefully tied to prevent the loss of arterial blood ; but if the spinal marrow be destroyed, all the vital phenomena cease, although respiration is continued. If a portion of it only be destroyed, life ceases only in those organs which receive their nerves from this part. The medulla oblongata is â– then not so important to all the organism, except as a medium. The true source of the preservative power of the nervous system resides in the posterior and inferior part of the encephalon and in the spinal marrow, and the integrity of all these parts is absolutely necessary to maintain life. This is farther proved by the fact, that although when part of the spinal marrow is destroyed, the vital phenomena cease instantaneously only in those organs to which it sends nerves, yet the other organs also soon perish, and at the same time as when the heart is removed and the spinal marrow uninjured. The destruction of the nervous system appears then to cause death by checking the circulation of the blood. Hence why the motions of the heart become much weaker when a part of the spinal marrow is destroyed ; and the reason too that when a considerable part of this cord is destroyed, life remains so much longer if the circulation be carefully restricted to a few organs, and the relation between the extent of the circulation and the force which remains in the heart after the lesion of the spinal marrow, be more favorable.

§ 195. The nervous system is also the medium bertveen all the organs. It unites them all, and changes in one are felt not only in the central mass, but also produce changes in the other parts of the body. It is then the organ of sympathies.

§ 196. The texture of the nervous system and the numberless communications of its different parts, greatly favor the development of sympathies. The plexuses of the nerves seem to be the medium of these sympathies, since they unite the filaments of the different nerves ; so that the branches given off by them, are always composed of filaments from two or more of these different nerves.

The nervous filaments separate and unite in the ganglions also. Hence they have been regarded in the same light as the plexuses, and their uses have been considered —


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1st. To increase the ramifications of the nerves, and to render them more minute, since on entering them, the nerves abandon their neurilemma, and are reduced to their constituent filaments, which receive a thinner and softer envelop when they emerge.

2d. To facilitate the passage of the branches of the same nerve to different organs, and to guard them against the dangers which might attend them in a long course.

3d. To unite in a single trunk several filaments of one, or of different nerves, or the different roots of the same nerve.(l)

But, then, we cannot conceive why the ganglions differ so much from the plexuses, or even why they exist ; it seems, then, more natural to think, that these organs increase in some manner the action of the nerves, an opinion which many ancient and modern physiologists have sustained with different modifications.

§ 197. The ancient anatomists were more strenuous to prove the existence of these ganglions than to determine their uses ; still, Galen's opinion seems to have been, that they increased the action of the nerves. He says, “ Ubi enim aid longo itinere nervum est {natura) ducturum, exiguum aut motui musculi vehenienti ministraturum, ibi substantiam ejus corpore crassiori quidem, cÅ“tera autem simili, intercipit.”{2) Wilbs,(3) and Vieussens,(4) that they prepared, perfected, or modified in some manner the active principle of the nerves. We may consider as modifications of this theory the opinion of Lancisi,(5) that they possessed muscular fibres to quicken the course of the active principle of the nerves, to render this principle more prompt in obeying the impulse of the will, and that of Gorter,(6) who believed them designed to concentrate the blood vessels, which, bytheir action,favor the passage of the nervous fluid. Lancisi, Winslow, Lecat, Winterl,Johnstone,Pfeffinger, Monro, Bichat, Gall, and Reil, have considered them as small brains, secondary brains, sources to increase the nervous power, because they are, like the brain, composed of a white and a gray substance, and because the latter is as vascular as in the encephalon; and farther, in the fetuses destitute of a brain by primitive formation, or where the brain has been accidentally compressed, the substance which replaces it very much resembles, in color and consistence, the nervous ganglions ; and finally, because the nerves given off by the ganglions are larger and more numerous than those they receive. Even the analogy between the structure of the nervous ganglions, and that of the lymphatic glands has


(1) Meckel, Obs. anat.sur unnÅ“udougangliondusecondrameaudelacinquième paire des nerfs du cerveau, nouvellement découvert, avec l'examen physiologique du véritable usage des ganglions des nerfs, in Mém. de V Ac. de Berlin, 1749, p. 85-102. Zinn, ibid. p. 753 ; De l'enveloppe des nerfs, p. 144. — Scarpa, Ann. Acad. MutinÅ“, 1799, B. i. — Haase, De gangl. struct, p. 32-35.

(2) De usu part. carp. hum. B. xvi. c. v. The nervous ganglions were discovered by Galen. F. T.

(3) Descript, nerv., in Opp. omn., Geneva, 1695, p. 120.

(4) Neurogr. p. 193.

(5) Diss. de structura usuque gangliorum annex. Morgagni, advers. an. V.

(6) Chirurgia repurgata, Leyden, 1742, p. 184.


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been adduced in support of this hypothesis, because it has been concluded that their functions ought also to be analogous.

This opinion is far from being contradicted by asserting, that the existence of the animal spirits is not demonstrated, which, according to the ancient physiologists, were produced, elaborated, kept in reserve, and rapidly propelled by the ganglions,(l) or that the structure of the organs which secrete them ought to be much more delicate, and that the mass of nervous substance does not increase in the ganglions, but that in them the filaments of the nerves are only divided into smaller filaments ;(2) and finally, that the structure of these ganglions is not similar to that of the brain.(^3) The imponderable principle which acts in the nerves is not what the ancients termed vital or animal spirits, and although we are now better acquainted with its laws, although we suspect it extends throughout ail nature, this knowledge does not atfect the state of the question in the least. We know of no other organ which can secrete it, except the gray and white substance, and both of these exist in the ganglions. But the ganglions are similar even in this respect to the brains, and although the anatomy of the superior animals does not prove this identity, we carmot doubt it, when we compare the ganglions and the brain of the inferior animals ; in fact, it often happens in these animals, that the different ganglions have the same inner and outer structure, and the same volume, as the brain.

We may, then, consider this opinion as demonstrated generally, although its different modifications are somewhat erroneous. Thus, for instance, Lancisi's assertion is untrue, that the function of the ganglions is to determine the flow of the vital spirits into the voluntary muscles ; for the organs which receive their nerves from these enlargements are in fact the involuntary, such as the heart, viscera, &c., although he maintains the contrary. It is, then, much more correct to say with Johnstone, that the ganglions interrupt the influence of the cerebral action on the organs, and to admit, with Haller and Metzger, that they blunt the sensations, in short, that the organs to which they send their nerves are more insulated than the others from the rest of the nervous system. In fact, the nerves of several of the voluntary muscles also have ganglions ; but they are formed from their posterior roots alone, and these do not unite to the anterior, till after the ganglions are produced. ' Finally, from what has been stated above(§ 182), it is wrong to say that the ganglions are situated in the course of the nerves to interrupt the cerebral influence ; the nerves emerge from the ganglions and are connected with the rest of the nervous system only by intermediate filaments ; the ganglions are centres, and hence the organs which they animate are insulated.

It follows, then, that several functions which have been considered as so many principal functions of the ganglions, are merely subordinate

(1) SÅ“tnmerringr, Nervenlehre, p. 130.

(2) Haase, loc. cit. p. 19, 20.

(3) Haase, loc. cit. p. 25.


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/

4

and infeiior, or rest only on false suppositions. Thus, according to Zinn, the ganglions are designed , to give a cellular envelop to the nerves which come from them. But the relation of the cellular tunic of the nerves with the ganglions, does not differ from that of the neurilemma with the pia mater of the brain or spinal marrow. It appears wherever a nerve is formed. Nor is the use of the ganglions to unite the different filaments of the nerves in a single trunk, as Meckel has pretended. This anatomist rested his opinion principally on the fact of the ganglions of the spinal marrow ; but Haase has demonstrated the incorrectness of the pretended fact. It is true that the nervous filaments ramify and interlace in a thousand ways in the compound ganglions ; but the same is the case in the brain and spinal marrow. We then have more reason to say, that the ganglions establish a contrast between the nerves which they give off and those which they receive; since the former are reddish and soft, and they are easily distinguished by their color and degree of solidity from those with which they anastomose.

§ 198. The nervous system differs considerably during life, both in itself and in its relations with other organs.(l)

The following are the most remarkable peculiarities in this respect : We have already observed (p. 45) that the nervous system is one of the first, if not the very first, which appears. Are all its parts seen at once, or successively 1 If they arise in succession, in what order do they appear ? This is, perhaps, no place to decide whether the nerves appear in those regions of the body which are formed after the others, later than in those parts which show themselves the first ; if, consequently, they develop themselves first or last irr the extremities. The problem reduces itself to determine if the central and peripheral parts do or do not arise at the same time, aird if the latter be true, which appears first. As the rrervous and vascular systems, and the intestinal carrai, are formed errtrrely or almost entirely together, the smallness of the objects reirders it almost impossible to determirre if the parts which are first seen, be the cerrtral parts of the rrervous system, or if they belong to the vessels, or to the intestines. Analogy favors the first hypothesis ; for in many worms we firrd only a single cord extending the whole length of the body, which does not give off atry nerves ;(2) arrd also different orgarrs, particularly the heart, the intestinal canal in the animal series, and even the whole body of the fetus, form in this manner, that is, we see the trunk first, and then the branches wlrich proceed from it.

(1) J. and C. Wenzel, loc. cit. chap. 27, 28, 29, 31, 34. — DœlHng'errs, Beitrœge zur Entwicklungsgeschichte des menscMichon Gehirns, Fvant, 1814. — Ackerman, /tesystematis ncrrciprimordiis, Heidelberg-, 1813. — Carus, loc. cit. p. 262-265 and 277-297. Meckel, in the Deutches Archiv Jür die Physiologie, 1815, vol. i. chap. 1 and 3.

(2) Cuvier, Anatomie comparée, vol. ii.


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But which of the central parts appears first ? There are two central masses, formed one by the encephalon and the spinal marrow, the other by the ganglions of the grand sympathetic nerve (p. 177). Does the former appear before the latter ; and are certain parts of these two masses formed before the others ?

The mmst probable opinion is that which attributes priority of origin to the encephalon and spinal marrow. This is supported,

1. By observations on the fetus ;(l) and,

2. By the analogy of the development of the nervous system in the animal series ; for that part of the system found in imperfect animals corresponds to this portion.

The same reasons should apparently lead us to think that the spinal marrow is formed before the brain. We may add to these the following ;

a. The size of the brain in proportion to that of the spinal marrow always diminishes as we descend the animal scale, h. The spinal marrow is perfected long before the brain, c. We sometimes see deformed fetuses in which the upper part of the body, and consequently the brain, is deficient, but never those in which the brain and upper part of the body are alone formed.

Other arguments have also been adduced to favor the priority of the spinal marrow. Some have thought to d*emonstrate that it was indispensable, by saying that “ the central organ of sensitive life ought necessary to develop itself at the same time with the heart, the central organ of vegetative life.”(2) But, as the spinal marrow appears before the heart, as in the fetus ; and, as in some animals, (insects,) we find nerves and even a spinal marrow, but no real heart ; and, as in the invertebral animals, the position of the heart is not constant, although that of the central part of the nervous system never varies, this explanation, imagined to establish that the spinal marrow necessarily precedes the brain, is as little plausible as most explanations of the same kind.

Ackermann has advanced another opinion, to which it may be objected that it does not rest on observation. He thinks that the sympathetic nerve is formed first, and thai its priority is equally necessary, because the heart, the organ possessing the highest degree of vital energy, is the centre of vegetative life. According to Ackermann, in fact, the globules of the blood pass through the substance of the heart, and arrange themselves in a series, to produce the fibres of the nerves, the softness and transparency of which he considers as another proof of this priority. He admits that the nervous system reaches the skull along the large vessels which arise from the heart, and that its mass gradually increases, to form the encephalon and spinal marrow ; that the latter is formed liy the brain, and is a prolongation of the cerebrum and cerebellum. Against this

(1) Malpighi, De ovo încubato, Op. anaf:, London, 1686, p. 4. Post diem inte f ru m — i res ampliores vesiculce, cum producta spinali medulla ; and in the Appendix : Uabcnte die — spinali medullce — cui vesiculce cerebri appendebantur.

(2) Cams, loc. cit., p. 78.


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hypothesis may be adduced most of the objections to that of the nervous system necessarily appearing at the same time as the heart, to contrast with it, and also the arguments which demonstrate the .priority of the spinal marrow.(l) In truth, Ackermann admits this priority of the spinal marrow, which he construes favorably to his hypothesis, saying that the nervous system of the invertebral animals correspoirds to the great sympathetic nerve of the superior arrimais, but not to their encephalon nor to their spinal marrow ; but this comparison is not correct. (2) In fact, the arrangement of these systems in the invertebral animals proves that it may be compared to the cerebro-spinal system, since, 1st, the nerves come from its cerrtre, and they are seen to arise from the same place in the superior anirrrals ; 2d, some parts of this nervous system are developed in the upper classes of the invertebral animals, as the cephalopodous mollusca, so as to resemble the brain ; finally, in these same animals we see a second nervous system, which corresponds to the sympathetic nerve, and which communicates with the other, in the same manner as in the superior animals. Let us also add, that if Ackermann's hypothesis be correct, there should be a period of life when the sympat.hetic nerve is much greater than the brain and spinal marrow, or at least should be largely developed in proportion to them ; but this is not the case. Besides, the experiments of Le Gallois have proved that the life of the sympathetic nerve and of the organs animated by it depends on the spinal marrow,(3) which could not be true if this nerve were formed before all the other parts of the brain, and if the spinal marrow were only an expansion from it.

According to Ackermann's hypothesis, the spinal marrow is not formed before the brain. This physiologist thought to reverse the argument drawn from acephalous monsters, by saying that in this monstrosity the brain is never primitively deficient, but that it has been destroyed by disease ; but this etiology of acephalia is admissible only when it is applied to monsters which have the body perfectly developed, but not the skull. There, in fact, every circumstance induces us to think that the brain, developed more or less irregularly according to the primitive type of the fetus, has been destroyed by an accumulation of serum. But we must distinguish these cases from .the true acephalia, where most of the upper half of the body is deficient, and there is no trace of its having been destroyed. Besides, even when this argument in favor of the priority of the spinal marrow is refuted, all the others retain their weight.

§ 199. It is then almost demonstrated, that the spinal marrow is that part of the nervous system which is first seen. But the brain soon appears at its upper extremity. This conjecture seems very probable

(1) Carus (loc. cit., p. 79) has made g'ood use of these reasons ; but, unless we are much mistaken, he has collected them against himself.

(2) At least Ackermann's reason is incorrect, that the sympathetic nerve, as an inferior nervous .system, must develop itself in the class of animals lower than where the more exalted brain and spinal marrow arc found.

(3) Le Gallois, Exp. sur le principe de la vie, Paris, 1812, p. 151.


OF THE NERVOUS SYSTEM IN THE NORMAL STATE. 193

from the progressive development of this organ in the fetus and in the animal series, since those parts which are situated the farthest forward, and are consequently the most distant from the primitive source of the spinal marrow, are developed the slowest, that is, they appear and enlarge the last. So too the great sympathetic nerve develops itself in front of the spinal marrow, in the form of a series of ganglions, which communicate with it and with each other by medullary cords. The brain and sympathetic nerve retain the distinctive characters of secondary formations longer than the spinal marrow. They preserve them even through life, since the different masses of ganglions which form them do not unite in one, but represent a series of organs more or less similar, as in the nervous system of the invertebral animals. On the contrary, the spinal marrow forms a single mass, in which we distinguish only two lateral parts, and which, examined from one extremity to the other, no where resembles a series of ganghons. The great sympathetic nerve, which is only an imperfect repetition of this organ, appears later even than the brain, if we may judge from its imperfect appearance ; for its component masses are still more distinct and separate than those of the encephalon.

§ 200. The nervous system, proportionally speaking, is much larger, softer, and moister in the early than in the subsequent periods of life. The reason that, the proportion of the liquids exceeds that of the solids is that the parietes of the permanent cavities are much thinner when the organism is younger, and because some of its cavities, as that of the spinal marrow, are soon obliterated.

The texture of the nervous system differs remarkably at different periods of life in this respect, that at first there is no distinction between the gray and the white substance, and that all the nervous mass has at first a grayer tint.

It whitens in the nerves and in the spinal marrow sooner than in the encephalon, within which the medullary substance is darker than the gray substance, even sometimes after birth ; this arises from its great number of vessels.

The lower parts of the brain assume their medullary appearance before the upper portions. ^

The nervous system differs also in other respects at different periods of life. At first, its surface is perfectly smooth, and its proportional size and the forms of its different parts do not remain the same. Thus, at first the spinal marrow fills the whole length of the vertebral canal, the cerebellum is smaller than the tubercula quadrigemina, and these are as large as the cerebrum.

§ 201. As the sexual differ'ences, we shall mention that the volume of the brain is larger in proportion to the nerves and the rest of the body in females, than in males ; and for the differences of races, that the nerves are proportionally larger in the negro.


VoL, I.


25


194


general anatomy.


ARTICLE SECOND.

OF THE NERVOUS SYSTEM IN THE ABNORMAL STATE.

§ 202. We shall commence t he history of the anomalies of the nervous system by that of the accidental injuries with which its form may be affected, as this will naturally lead us to speak of its power of regeneration.

The changes in the structure of the nerves, caused by the wounds of these organs, differ much from those seen in other parts of the body in similar cii'cumstances.

When a nerve is divided, its extremities always swell into a larger or smaller tubercle.(l) The color of this tubercle is grayish, and it is often so hard and solid that the scalpel glides off when cutting it, and the sound resembles that from cutting cartilage. The size of this tubercle is in direct ratio with the abundance of cellular tissue, and to the time which has elapsed since the wound. It not only enlarges in time, but also becomes harder.

The tubercle of the upper extremity is smaller, but as hard as that of the lower. That portion of the nerve below the section, withers and loses its distinctive color.

In amputations, this tubercle seems not to develop itself exactly at the extremity of the divided nerve ; at least, .Van Horn(2) has found that an inch above the wound, the nerves were blended with the granulations of the muscles, and could not be distinguished from the mass. One month after the operation, they were reddish internally and externally, and the tubercle distinguished from the end of the nerve by its whiteness, was then situated still higher. The lower end of the nerve is wasted more or less, like tjjat of all other organs. Finally, the tubercles are seen both in the small and the large branches of the nerves, and they remain apparently during life.

§ 203. If the lower part of the nerve has' not been removed, it unites with the upper portion. But observers are not agreed on the nature of the uniting substance. Some think it real nervous substance, while others consider it simply as a cellular tissue, or coagulated lymph, which can never acquire the peculiar structure of the nerves. Hence the dispute in regard to the regeneration of these organs.

There are two ways of ascertaining if an organ be renewed ; these are, to study its functions, and to investigate the nature of the substance formed in place of the portion removed. The first method is very uncertain, since the mechanical arrangement of the nervous system is such, that the nerve which is divided may be replaced by the anastomosing filaments, and a substance imperfectly analogous to that which

(1) Arnemann, Ucber die Reproduction der Nerven, Gottingen, 1786, "p. 48. — Id. Verseuche über die Regeneration der Nerven, Gottingen, 1787.

(2) De iis quae in partibus membri, prœsertim osseis, amputatione vulneralis notan da sunt, Leyden, 1803, p. 33-35.


OP THE NERVOUS SYSTEM IN THE ABNORMAL STATE. 195


normally exists, is sufficient to unite the two extremities so perfectly, that the functions may be performed -with perfect regularity. The second method is more certain, but is also liable to deceive.

Cruikshank,(l) Haighton,(2) Fontana,(3) Momro, Michaelis,(4) and Mayer, (5) reasoning from different researches, have admitted that the nerves have the power of perfect regeneration. Arnemann, on the contrary, thinks himself authorized, by numerous observations, to deny it. He states(6) that the extremities of the nerves are always united by cellular tissue, condensed by inflammation, which sometimes acquires the hardness of cartilage, and fills up the space more or less perfectly, accordingly as the nerve was more or less surrounded with cellular tissue, and that it gradually and slowly becomes consolidated with the two extremities of the nerve. Munro(7) has also found that the newly formed substance has always a deeper color.

Fontana believed that true nervous substance was reproduced in some cases where he had removed from the intercostal nerve, a portion six lines in length, because that the nervous filaments passed tminterruptedly through this substance, in going from one end of the nerve to the other.

Michaelis removed portions of nerves, nine or ten lines long, and found, after eight weeks, that the extremities of these nerves were united, by a substance perfectly similar or nearly so, to the. nervous substance. The transition from the old to the new nerve was but slightly perceptible by the microscope.

Mayer, having removed portions one or two lines long, found the extremities of the nerves reunited by filaments more or less fine, which, Kke the true nervous substance, did not dissolve in nitric acid ; but, on the contrary, became harder, and consequently possessed one of the most essential qualities of tliis substance.

Haighton divided in a dog the pneumogastric nerve on one side, and six weeks after, that of the opposite side ; in six months the animal had entirely recovered. But all dogs in which the two par vagum nerves were cut simultaneously or shortly after each other, died. Hence he concluded, that death did not occur in the first case, because the wound of the nerve was cicatrized perfectly in six weeks. Still the function might have been performed by the other nerves, which, perhaps, had enlarged. If this was the case, the animal would continue to live when the two pneumogastric nerves were divided simultaneously. Haighton repeated this experiment, but the animal died : proving that the functions were re-established, because the substance of the nertms was reproduced.

(1) Hxperiments on the nerves, <^c. in Rcil, Archiv, vol. ii. p. 57-81.

(2) Experiments on the reproduction of the nerves, ibid. p. 79.

(3) Versuche über das Viperngift, part ii.

(4) Véber die Regeneration der Nerven, Cassel, 1785.

(5) Reil, Archiv Jur die Physiol, vol. ii. p. 449.

(6i Loc. cit. p. 47.

if) Weber das Nervensystem, p. 94.


196


GENERAL ANATOMY.


Arnemann has rejected all those experiments in favor of the reproduction of the nerves, in which they were merely divided and no portion of them was removed, saying, that in these cases there was no reproduction. But the difference in the cicatrization of wounds, with or without loss of substance, is only in degree , since the simple wounds do not unite immediately, and the lymph which transudes gives rise to a new substance which joins their two extremities. The above mentioned experiments seem to authorize the belief, that the new substance, which is homogeneous in the wounds of all organs, may gradually become real nervous tissue. Farther, we cannot conclude that this new substance is not nervous, because its characters differ from the old nervous substance ; for the bones, when newly formed, also vary in form and structure from those which are old.*

Wounds of the encephalon, when attended with loss of substance, also cicatrize by a new substance there developed, which is unlike the normal substance of the organ. It is more yellowish, and more easily distinguished from the gray and the medullary substance. The yellow substance of the brain resembles it the most. Its tissue is loose and soft, and sometimes entirely mucilaginous. However, the circumvolutions of the brain are sometimes formed from it. It generally closes the wound entirely, its edges approaching the centre. Another circumstance very favorable to the cicatrization of wounds of the brain, is the enlargement of the ventricle on the diseased side, while neither life nor health are affected. We sometimes find a viscous or coriaceous matter within the new cerebral substance, which Amemann thinks is formed by the coagulable lymph, thrown out from the wound of the temporal muscle. It is firmer and redder than the new cerebral substance, and is usually filled with new vessels. (1)

§ 204. The principal anomalies in the form of the nervous system are :

1st. Its absence, totally or partially. A deficiency of the whole system is rare, (2) and is usually attended with an imperfect development of the whole organism, which is undoubtedly caused by it.

A partial deficiency is more common. Usually a greater or less portion of the brain is absent, and it sometimes happens that the spinal marrow does not exist, or that a part of it is wanting. Sometimes the whole brain is deficient, while the spinal marrow is perfectly developed. This state, attended or not with the imperfect formation of the adjacent parts of the body, is called acephalia, or more strictly anencephalia. We shall mention its principal characters when we


♦ M. Flourens, in a Memoir in the Ann. des Sc. Naturelles, Peb. 1828, states that, having repeated the experiments of Fontana, Montana, Cruikshank, and others, on the reunion of the divided extremities of the same nerve, he sought to determine the effects resulting from uniting the ends of different nerves ; he therefore kept them in contact- — Union took place in every instance. In some of the cases, the return of the function was complete ; in others, it failed. In all, the transmission of irritations by the united nerves was perfect. — Am. Med. Journ. no. vii.. May, 1829.

(1) Arnemann, Versuche über das Gehirn, und Rückenmark, Gottingen, p. 187.

(2) The only case we know is that mentioned by Clarke, Phil. Transact. 1793, p. 15U164.


OP THE NERVOUS SYSTEM IN THE ABNORMAL STATE. 197

have described the brain.(l) We shall only say here, that the absence of the spinal marrow (at least such as might be considered original) has never been observed in a fetus where the brain was perfectly developed, and that anencephalia is more frequent in the female than in the male.

In regard to the nerves, they are rarely wanting. The first degree of this anomaly is the partial interruption of a nervous trunk ;(2) of this the nervous system of organic life (§ 182) sometimes furnishes examples.

The nervous system is never doubled, nor multiplied, at least when the body is not.

2d. An excess or deficiency of volume.

An excess in size is rare when the structure of the nervous system is otherwise normal. (3) As to the contrary state, an abnormal smallness, although the nerves never are deficient, this is not more common than original delations of formation. Atrophy or wasting of the nervous system is seen more frequently ; it may be primitive, as in tabes dorsahs, or consecutive, and accompanied by the loss of the function of the organ. Thus, when the eye is destroyed, the optic nerve wastes. The nerve, however, then becomes not only thinner and finer, but its texture changes, it hardens, is grayer, and more transparent.

We may here mention the dropsy of the nervous system, where the solids have not the same relation to the fiuids, which often accumulate in enormous quantities. This state is congenital more frequently than it is developed after birth. In the first case, the whole nervous system is generally affected ; in the second, it is confined to some of its parts, principally to the encephalon ; its more intimate relations must be mentioned in the description of the brain and nervous system.

3d. Anomalies of situation and form, particularly if congenital, are very rare. These also belong to descriptive anatomy. Among the accidental, we should distinguish lacerations, to which the brain is exposed, from an effusion of blood within it. The changes which occur in this organ belong to special anatomy.

§ 205. Among the alterations of texture of the nervous system, we mention:

1st. Anomalies in the color. This is rarely seen, unless accompanied by other alterations of texture. The whole or a part of the nervous system, however, is more or less tmged with yellow in jaundice.

2d. The abnormal softness and hardness exist alone or together ; so that one portion of the nervous system is much harder and another much softer than usual.

Weinhold asserts that the nerves are unusually soft or fluid in persons affected with typhus. (4) The brain is sometimes softer and sometimes harder than usual in maniacs. Frequently, too, it is harder in some

(1) See our Path. Anat. vol. i. p. 195.

(2) See our Path. Anat. vol. i. p. 392.

(3) See our Path. Anat. vol. i. p. 392.

(4) Hufeland, Prakt. Bibliothek, vol. xxxi. p. 501.


198


GENERAL ANATOMY.


points, and softer in others, in people disposed to epilepsy. In hydrocephalus, its parietes are generally tlrinner and softer.

§ 206. JVew formations in the nervous system are not rare. Repetitions of the normal tissue are extremely uncommon. Bones and fat are the only parts, to our knowledge, which appear, sometimes in the substance of the brain, rhore rarely in the nerves around them. But it is by no means uncommon to find accidental osseous tissue in the dura mater.

On the contrary, abnormal formations of different kinds are not rarely developed either in the substance or on the surface of this system, especially on that of the brain.

Encysted tumors connect these repetitions of the normal tissues with the new formations. They contain various liquids, and are more rare in the nerves than in the encephalon, particularly m the ventricles and choroid plexuses.

Very hard rounded tumors, of a yellowish white color, perhaps like the fibro-cartilages, as they have a fibrous structure, are sometimes found in the nerves,(l) and also in the bram. When developed in the nerves they occupy the intervals between their fibres.

The brain is also frequently the seat of white, hard, round tumors, very analogous to scrofulous tumors, which would doubtless be found also m other portions of the nervous system, if they were carefully examined. They are almost always united to the cerebral substance. Some other tumors, resembling fungous tumors, and which perhaps are a repetition of the mucous tissue, are more rarely found, but only in the brain. They are red, very vascular, soft, and adhere but shghtly to the substance of the brain.

Finally, loose hydatids develop themselves both in the ventricles of the brain, especially in the lateral ventricles, and even in its substance. In treating of the special anatomy of the nervous system, we shall examhie these anomahes more in detail.


OF THE SPECIAL ORGANIC SYSTEMS.

§ 207. After the description of the general organic systems follows that of the special (§ 16).

Among these we consider, 1st, The osseous system, inasmuch as several circumstances in the history of the other systems are to be fully understood only by an acquaintance with it, especially with its external form.


(1) Cheselden, Anatomy of the human body, p. 256, tab. 28. — Home, An account of an uncommon tumor found in one of the axillary nerves, in the Trans, for the improv. of med. and surg. knowledge, vol. ii. no. xi. — Spanffenberg', Sur les gonflemens des nerfs, in Horn, Archiv, für med. Erfahrung, vol. v. p. 306. — Alexander, De tumoribus nervorum, Leyden, 1800. — Wood, On painful subcutaneous tubercle, in the Edinb. med. and surg. journal, vol. viii. no 31 and 32.