Paper - The development of the cerebral ventricles in the pig (1913)

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Heuser CH. The development of the cerebral ventricles in the pig. (1913) Amer. J Anat. 15(2): 215-.

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This historic 1913 paper by Heuser describes respiratory development prenatal and neonatal period


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The Development of the Cerebral Ventricles in the Pig=

Chester Heuser

Chester H. Heuser

Harvard Medical School, Boston, Massachusetts

Twenty-Six Figures

Introduction

In this study of the cerebral ventricles of pig embryos three methods have been employed — wax reconstruction, dissection, and the making of minute casts. Wax reconstructions of the ventricles have the advantage of large size. The volume of the various cavities of the brain can best be estimated by immersing portions of such reconstructions in water, and observing the displacement. From these observations the actual size of the ventricles can be readily calculated. But dissections and casts are more accurate for showing details, as, for example, the neuromeral grooves; and most of the drawings have been made from such preparations.


Brains of pig embryos measuring from 12 to 45 mm. were dissected under the binocular microscope, with finely ground instruments. Some of the dissections were designed to give a median sagittal view of the right half of the entire brain. The embryo, fixed preferably in Zenker's fluid, was held in a mass of cotton wet with alcohol, between the thumb and index finger of the left hand; and under a small stream of alcohol, a longitudinal cut was made with a sharp safety razor blade. Very perfect cuts can thus be prepared, such as will pass between the hemispheres and thence backwards, sectioning the infundibulum, corpus mamillare and other divisions of the brain almost exactly in the median plane. Mesenchyma which covers the hemisphere, olfactory lobe, or other portions which it is desired to expose, can be easily removed with delicate needles and forceps.


Casts of the ventricles, in embryos measuring from 12 to 22 mm., were made after the following method. Longitudinal sections of the entire embryo, made slightly to the right side of the median plane, were prepared as above described. Then, under the binocular microscope, obstructing portions of the brain walls were dissected off, and the ventricles were cleaned of all precipitation with a small brush and syringe. Next the embryo was taken from the alcohol and pinned down to a piece of cork and with narrow pointed strips of filter paper all the alcohol was removed from the cavities of the brain. In a large measure the success of the cast depends upon the completeness of the removal of the alcohol. The cast was made by filling the cavities with black wax with the aid of a fine electrically heated needle. A small piece of wax was carried with a cold needle to the proper place and then melted with the electric needle. This process was repeated until the ventricles had been filled. Then if desired, white wax was melted over the upper surface of the dissection for holding the parts more closely together. Moreover, the white background thus provided contrasts sharply with the black cast. Lastly the preparation was turned upside down and the brain wall was carefully dissected away from the wax. For making a permanent preparation of the cast, it is best to mount it in a dry cell on a microscopic slide. Casts thus made show a little more than one-half the ventricles. They can be studied with the binocular microscope, and drawings can be made quite as satisfactorily as from larger models. After embryos exceed 20 mm. in length the interventricular foramen is so small that it is difficult to get the lateral ventricles completely filled, and after 24 mm. the lateral recesses can hardly be cast.


For the electric needle a piece of no. 18 copper wire is coated, except for about 15 mm. at one end, with a thin layer of some insulating paste which will harden and be resistant to heat. The commercial 'caementium' is very satisfactory. The bare end is ground down to a fine point which is the working part of the instrument. Behind this, covering a length of about 20 mm., a piece of no. 32 German silver wire, about 20 cm. long, is wrapped around the insulated copper wire, the coils being well insulated from each other and covered with caementium. Attached to the ends of the German silver wire are small copper wires which run to a lamp board. The lamp board, with the sockets connected in parallel, serves as a rheostat, and any desired temperature can be obtained by turning on the proper lights. One 50 e.p. globe allows about the desired amount of current to flow. A larger electrically heated smoother for wax models and an electrically heated knife for cutting wax plates, which were used in making the models, will be described at a future date.

Those who study the nervous system from the standpoint of comparative physiology regard the "functional system of neurones" as the real unit of the nervous system. Thus Herrick ('08), tin discussing the morphological subdivisions of the brain, refers to the influence of metamerism as primitive, dominating the subdivision of the nervous system of lower vertebrates. He further states that transverse divisions, such as the diencephalon and mesencephalon, are not ' natural regions' because the primary metamerism has ceased to be an important factor. But the anatomical subdivisions exist no less than the physiological, and although their significance may not be profound, they form a convenient basis for description. In the following account the primary divisions of the brain will be considered in this order — fore-brain, mid-brain, hind-brain. Reference will be made especially to the casts and models of the ventricles, but the wall of the brain must also be studied as the changing structure which modifies the cavities within.

Fore-Brain

A model of the cerebral ventricles of a 5.1-mm. embryo, the youngest one studied, shows that the three divisions of the brain are distinctly marked off from each other, and that the fore-brain is aheady subdivided into telencephalon and diencephalon. Johnston ('09) states that the boundary between the telencephalon and the diencephalon is determined in mammals, as well as in lower vertebrates, by the velum transversum above and the primitive optic groove or postoptic recess below. This subdivision is distinct in the young pig studied as seen in figure 4. In the model very slight lateral swellings from the telencephalon indicate the cavities of the rudimentary * cerebral hemispheres. The diencephalon shows a division into two parts or neuromeres, the first or parencephalon, and the second or synencephalon of Kupffer ('03). The relatively large cavities of the optic vesicles extend out from the antero-ventral part of the diencephalon. Almost one-fourth of the length of each vesicle, representing the optic stalk, extends nearly straight out laterally, and the remainder bends sharply toward the mid-brain.

In an embryo of 12 mm. the lateral ventricles have expanded considerably and they now slope outward forward and slightly upward from the interventricular foramen. The foramen is almost circular in outline and has an area of about 0.428 sq. mm. In the cast (fig. 5) the rounded mass of wax filling the lateral ventricle shows a slight concavity below, which has been produced by the developing corpus striatum. This body arises as a thickening of the ventro-lateral wall of the hemisphere, as seen in the dissection, figure 6. This figure, it may be noted, bears a very striking resemblance to the reconstruction of the brain of Anguis fragilis (40-50 somites), published by Kupffer ('03, p. 220, fig. 224). In both, the parencephalon and synencephalon are sharply marked off from each other. Two swellings, which correspond with these subdivisions, are seen in the cast (fig. 5). The parencephalon is larger than the synencephalon, and its cavity produces a more extensive swelling, which however, is quite low.

The mamillary recess and the infundibulum below it, neither of which had appeared in the 5.1-mm. embryo, are now very distinct. The velum transversum, a portion of which is shown in figure 7, is well developed, producing a deep inward bend of the anterior wall of the fore-brain above the hemisphere.

The brain of a 17-mm. pig embryo, as seen in median section (fig. 8), shows a prominent corpus striatum, above which is the interventricular foramen. The foramen is now crescentric, since it has been invaded from below by the corpus striatum, but notwithstanding the growth of the entire embryo, its area has become actually reduced. It measures about 0.315 sq. mm. As seen in the dissection, the lower portion of the corpus striatum is bounded behind by a deep groove which is continuous with the optic recess. This groove appears as a ridge upon the cast (fig. 9), and in front of it the position of the corpus striatum is indicated by an excavation. Above this hollow is seen the inferior horn of the lateral \'entricle. The outline of the ventricle is no longer round, as in the 12-mm. embryo. It is prolonged anteriorly or downward to form the first indication of the olfactory lobe, and posteriorly or above, it is somewhat flattened. This upper portion terminates in the inferior or descending horn. Fraser ('94) has referred to this horn in an abnormal human adult brain as in ' ' reality ascending" and Thompson ('08) similarly states that "from the developmental point of view, this descending horn is in reality an ascending horn." In pig embryos, however, as seen in figures 5 and 9, its primary direction is apparently ventral to the cerebral axis so that the inferior horn may be said to descend, even in early stages. The cavity of the lateral ventricle is seen laid open in figure 10. It differs from that of the 12-mm. pig embryo (fig. 6) since it has been invaded by a prominent chorioid fold. This fold is a lateral extension of the velum transversum, and it consists of vascular mesenchyma covered by the thin wall of the brain. At this stage its ventricular surface is perfectly smooth, but in a 22mm. embryo the chorioid fold has developed a vascular fringe which appears as a plaited frill. This is shown in figure 13.

The walls of the diencephalon in the 17-mm. embryo have thickened considerably so that the external depression between the parencephalon and the synencephalon has become almost imperceptible. Their cavities however, can be distinctly seen when the dissection of the brain is studied (figs. 8 and 9). The mamillary recess now projects out some distance from the third ventricle. Midway between this recess and the infundibulum the floor of the brain has thickened to form the tuber cinereum. The optic thalami, represented by the thickenings of the lateral walls of the diencephalon, have developed to such an extent that they have already partially fused with the corpus striatum. The place of fusion appears as an interruption of the groove between the interventricular foramen and the optic recess.

The median section of a brain of a 22-mm. embryo (fig. 11), as compared with that of the 17-mm. specimen, shows several new features. Along the cut edge dorsally, the pineal body has appeared as a slight elevation. Within the third ventricle, the thalamus has enlarged, and the corpus striatum appears as if pushed forward before it. Between the corpus striatum and the upper part of the thalamus, the interventricular foramen is seen as a slit, which arches up over the corpus striatum, being widest immediately under the velum transversum. The area of the aperture has become further reduced. Between the corpus striatum and hypothalamus, the optic recess appears as in the 17-mm. specimen. Somewhat further back, and parallel with it, is the recessus infundibuli, and between the two grooves made by these recesses, is the pars optica hypothalami. This is convex toward the ventricle. Between the hypothalamus below and the thalamus above is the sulcus hypothalamicus (B.N.A.) or sulcus limitans (His '93) — a groove which continues from the mid-brain downward and forward becoming somewhat indistinct above the pars optica hypothalami. Reichert ('61) described this groove in the brain of a pig embryo (also in cat and human embryos) as extending from the foramen of Monro to the entrance of the aqueduct of Sylvius, and he named it the sulcus of Monro. In fig. 12 an extension may be traced from the sulcus to the lower end of the interventricular foramen; another extension proceeds toward the recessus postopticus. But the main continuation is probably that which ends in the optic recess. This accords with the opinion of His ('93, p. 177), and also of Johnston ('09, p. 517). The sulcus limitans is indicated in the embryo of 17 mm. and in younger specimens, but it is more distinct at 22 mm.

The median section of the 22-mm. embryo shows the uncut median surface of the right hemisphere, ending below in a rounded olfactory lobe. Extending from the lower border of this lobe toward the notch below the velum transversum, is a groove, which, with the lamina terminalis, bounds a triangular portion of the hemisphere. Smith ('03) named this triangular thickening the ' paraterminal body'. Herrick ('10) proposes to divide this body into a ventral component, the 'corpus precommissural,' and a dorsal component, the 'primordium hippocampi,' but these subdivisions do not appear externally in the 22-mm. embryo.

In the dissection of a 45-mm. embryo (fig. 14) most of the paraterminal body together with the adjacent medial wall of the right hemisphere have been cut off, thus displaying the structures within the ventricle. The corpus striatum is seen to be divided by a vertical groove into two portions. The groove is deep below but fades out above. Thompson ('09) has described a similar groove in a cat embryo 20 mm. in length, and he refers to the larger lateral and the smaller median subdivisions which are set apart by the groove as 'roots' of the corpus striatum. His ('89) described the corpus striatum as being composed of three limbs. In the 45-mm. pig there are also three limbs, but only two are seen in figure 14. The small median limb, which is not shown, fuses with the lamina terminalis just below the interventricular foramen. The groove is shown at x in figure 18, which is a frontal section through the head of a 45-mm. pig. The plane of this section is indicated in figure 14. The groove is best seen in the right side of the section, where the median subdivision may be observed to pass down toward the paraterminal body. In a section further back (fig. 19) the groove is quite shallow. Above the corpus striatum (figs. 14 and 19) the chorioid plexus is seen projecting into the lateral ventricle. The fold, surmounted by a frill, which was seen in the 22-mm. embryo, has given place to a very thin layer with many reduplications and subdivisions. Villi are nowhere present, but in thin sections the smaller processes extending out from the main folds may simulate them. Under the binocular microscope it is clearly seen that this plexus consists only of folds with secondary subdivisions. The plexus is attached along a fissure measuring 2.1 mm. in length, which extends backward from the interventricular foramen.

The caudal portion of the plexus — about one-fourth of the entire length — is very much attenuated. It forms a short free projection extending 0.18 mm. beyond the end of the fissure, and the free portion shows no secondary folds (fig. 21). The anterior portion of the plexus forms a larger free projection which extends 0.72 mm. past the front end of the fissure.

In the 22. mm. embryo (fig. 13) a slight invagination of the medial wall of the hemisphere, above the chorioid plexus and parallel with it, extends from the interventricular foramen backward into the inferior horn. This represents the hippocampus, which is better developed in the 45-mm. embryo. It is seen in figures 19, 20, and 21 (marked +).

Considered as a whole, the lateral ventricle has expanded greatly and may readily be divided into three parts — the anterior horn, which is in front of the corpus striatum; the body, which is above it; and the inferior horn, descending behind it. A cast of the left lateral ventricle is shown in side view in figure 16, and in ventral view in figure 17. The latter shows the large excavation made by the corpus striatum. Toward the olfactory lobe this concavity is bisected by a ridge, which lies between the large roots of the corpus striatum, as described in connection with figure 14. Below the concavity, in figure 17, there is a ridge which is fissured, posterior to the interventricular foramen, to receive the chorioid plexus. This ridge separates the hollow for the corpus striatum above, from that for the hippocampus below.

The lateral ventricle communicates with the third ventricle by an interventricular foramen which is smaller than in the preceding stages. The third ventricle has become reduced to a slitlike space, owing to the great thickening of the walls of the diencephalon. A portion of it has become practically obliterated. This is where the thalami have grown against each other (figure 21). They have not yet fused, however, to form the massa intermedia; that is the ependymal layer over each thalamus is still uninterrupted. Along the dorsal margin of the cleft, which represents the ventricle, there is a thin lateral expansion on either side (fig. 15). The expansion begins at the interventricular foramen, where it is broadest, and it diminishes backward, ending a short distance in front of the pineal recess. Thus the expansion is wedge-shaped when seen from above. The brain-wall which overlies this expansion is the tela chorioidea, which has a corrugated surface in relation with the vascular mesench^ma. Below and behind the thalamus is a deep groove — the sulcus limitans — which, as already described, sends prolongations to the interventricular foramen, recesses postopticus and recessus opticus. The sulcus is seen in section in figure 20, with the thalamus above and the pars optica hypothalami below.


The oldest embryo studied measured 260 mm. Its brain was dissected out, embedded in celloidin, and cut into sections 0.2 mm. thick. From these sections a wax model of the ventricles was constructed, as shown in figures 25 and 26. The three subdivisions of the lateral ventricle have become highly developed. The anterior horn, which in the 45-mm. embryo ended in a short and slightly pedunculated olfactory bulb, now extends through the olfactory stalk and terminates in the expanded ventricle of the olfactory bulb. The body of the lateral ventricle is corrugated above, w^here it is in relation with bundles of fibers in the corpus callosum. The inferior horn not only descends, but extends forward as a slender prolongation, which ends blindly in the temporal lobe of the brain. As seen from below, the cast of the lateral ventricle shows the concavities for the corpus striatum and the hippocampus respectively, separated by a ridge into which the chorioid plexus is invaginated. The ridges bounding the corpus striatum correspond with those seen in the 45-mm. embryo.

In the 260-mm. specimen, the interventricular foramen has expanded considerably, and its area was found to be 6.92 sq. mm. Extending backward from the foramen, between the region occupied by the thalamus below and the tela chorioidea above, there is a tubular expansion of the third ventricle, somewhat flattened dorso-ventrally. This corresponds with the much smaller expansion, T-shaped in section, which was described in the 45-inm. embryo. In the 260-mm. embryo there is a long caudal extension of the dorsal part of the third ventricle which curves slightly upward and forms the suprapineal recess. It measures about 5.6 mm. in length and extends backward with quite a uniform diameter of 1.4 mm. This conspicuous feature is not represented in the 45-mm. specimen. The cast of the cavity (fig. 25) is deeply corrugated on all sides by longitudinal folds. These accomodate branches of the medial cerebral vein. A large branch of the vein on either side produces a deep groove along the dorsal expansion of the third ventricle. Between the suprapineal recess above and the pineal recess below there is a well marked lateral compression of the ventricle, produced by the habenular ganglion. The conspicuous ridge at the lower margin, of this habenular concavity continues caudally into the pineal recess. Between the pineal recess and the groove for the posterior commissure there are two slight projections of the third ventricle (infrapineal recesses). The very extensive fusion of the thalami, forming the massa intermedia, has produced a hole in the model of the third ventricle. It is oval in outline, measuring about 4.6 mm. by 3 mm.

Mid-Brain

It is well known that in young embryos the cavity of the midbrain is very large, forming the middle cerebral vesicle. In the adult it is generally described as '^ reduced to a narrow slit— the aqueduct of Sylvius." Cunningham states that the mid-brain "is tunnelled by a narrow passage, the aqueduct of Sylvius, which extends between the fourth and third ventricles, "and Bensley ('10) writes: The mesencephalon is noteworthy in a mammal as lacking a ventricle. Its cavity is a narrow canal, the aqueduct of Sylvius . . . . " But Retzius ('00) described a spindle-shaped expansion in the middle portion of the cavity of the adult human mid-brain, and named it 'ventriculus mesencephali.' It will be shown that a distinct cavity exists in the mid-brain of the adult pig, comparable with that found by Retzius in the human brain.

In the 5.1-mm. pig (fig. 4) a slight constriction separates the caudal part of the diencephalon from the cavity of the mid-brain. Another slight constriction marks the position of the isthmus between the mid-brain and the hind-brain. The angle formed by a line passing through the axis of the diencephalon with another through the isthmus and cavity of the medulla, is very acute (30°) in this stage. In the adult it is very wide.

The cavity of the mid-brain continues to expand and becomes sharply marked off from that of the hind-brain at the isthmus, as shown in the 12-mm. embryo (fig. 5). Between the mid-brain and fore-brain, however, the cavity shows only a slight constriction, which is limited to the lateral surface. As seen in the cast neither the mid-dorsal nor the mid-ventral line is indented at this point.

Figure 9, of a 17-mm. embryo, shows that the dorsal surface of the mid-brain has become flatter than before and its caudal end projects further toward the hind-brain. This projection, on either side, marks the position of the future inferior colliculus. The ventricle of the mid-brain is somewhat quadrilateral in cross section, and in the cast it shows a prominent longitudinal ridge corresponding with the line of maximum width. The groove in the wall of the brain corresponding with the ridge may be referred to as the lateral sulcus (sulcus lateralis internus). It must not be confounded with the sulcus limitans which, in the cast, is a much less conspicuous ridge, more ventrally placed. The sulcus limitans is more evident in the dissection, figure 8. It separates a small thick-walled ventral zone from an extensive thin-walled dorsal zone. The ventral zones, on either side of the mid-ventral sulcus, form low rounded eminences projecting into the cavity of the ventricle which constitutes the tegmental fold of His. The lateral sulcus passes longitudinally through the dorsal zones, terminating on either side, in the projection which forms the inferior colliculus.

In a slightly older embryo (22 mm.) the dorsal wall of the mid-brain has become relatively thinner, and its ventricle has expanded greatly. At this stage it forms a very conspicuous portion of the whole ventricular system. Its volume is estimated at 4.1 cu. mm. Separate recesses for the inferior colliculi can now be recognized. In earlier stages the posterior overhanging portion of the mid-brain ended abruptly in a straight transverse line. In the 45-mm. embryo this border shows a deep median cleft, and each arm of the bifurcation thus formed represents the cavity of an inferior colliculus. In the 22-mm. specimen the cavities projecting backward from the dorso-lateral corners of the midbrain ventricle have just begun to develop.

In the 45-mm. embryo the third ventricle is connected with the cavity of the mid-brain by a more elongated constricted portion than in previous stages. At the anterior end of the midbrain ventricle there is a median dorsal extension 1.2 mm. caudad to the pineal recess. This outgrowth (figs. 14 and 15) which Ues just behind the posterior commissure is the incisura postcommissurahs. It is not present in the 20-mm. pig but is very distinct in the 45-mm. embryo. The ependymal and mantle layers but not the ectoglial layer of the brain-wall make a distinct outward bend above it. Caudad to the incisure, the dorsal surface of the mid-brain cavity slopes gradually upward to a height of 0.6 mm. and then extends nearly straight backward over the body of the cavity. The inferior collicular recesses are very much more distinct than in younger pigs.

The length of the mid-brain, including its collicular recesses is 5.0 mm. and- the width, in the widest part is 2.6 mm. The volume of the cavity is very much greater than in preceding stages and is now about 6.9 cu. mm.

A cast of the cavities of the mid-brain in an embryo measuring 110 mm. is of an irregular prismatic form as shown in figure 24. It presents a median dorsal ridge which extends from the incisura postcommissuralis posteriorly, ending in a median depression between the eminences representing respectively^ the cavities of the right and left inferior colliculi. The outer margin of the cavity of each inferior colliculus is continued forward as a prominent ridge, corresponding with the sulcus lateralis. This ridge flattens out rather sharply and completely a short distance behind the posterior commissure. At the base of the cavity of the inferior colliculus, a prominent ridge ascends from the isthmus, but it can be followed only a short distance behind the posterior commissure into the territory of the mid-brain, where it terminates. This ridge represents the sulcus limitans of the isthmus. Ventrally there is another ridge which may be regarded as the sulcus limitans of the mid-brain, although it is not continuous with the structure just described as the sulcus limitans of the isthmus. It arises beneath the latter in or near the median ventral sulcus. It then passes laterallj', diverging from its fellow on the opposite side. The point of widest separation is soon reached, after which the two sulci gradually converge, coming together in the mid-ventral line beneath the incisura postcommissuralis. The surfaces between the ridges on the cast are all concave, and in the central part of the mid-brain there are five surfaces — two dorso-lateral, bounded by the median dorsal ridge and the lateral ridges; two ventro-lateral, extending downward to the sulci liniitantes; and a ventral surface between these sulci.

The form of the mid-brain ventricle in the embryo measuring 110 mm. has been described at length, since subsequently it undergoes only slight modifications. This was determined by modelling the ventricles in the 260-mm. pig (figs. 25 and 26) and by making dissections of the adult. The ventricle of the mid-brain continues to increase in size but it does not keep pace with the growth of the adjoining cavities. The grooves remain as described, and the ventral surfaces, between the sulci liniitantes, are always subdi^dded posteriorly by a forward extension of the median ventral sulcus.

Hind-Brain

In the 5.1-mm. embryo the cavity of the hind-brain or third cerebral vesicle is elongated and quite straight. Behind the ventricle of the mid-brain (fig. 4) a well marked constriction indicates the future isthmus. Caudad to this, the cavity, or fourth ventricle, widens somewhat, and then slopes gradually through the medulla to the spinal cord. The low ridge which follows the line of greatest width corresponds at this stage with the line of attachment of the thin roof-plate, and not with the sulcus limitans. Along the ventral surface of the cast there is a sharp median ridge which represents the sulcus medianus of the rhomboid fossa.

Seven neuromeral grooves can be identified. The first produces a low but broad ridge on the cast anterior to the widest part of the rhombencephalon. Dorsally it flattens out before reaching the line of maximum width and ventrally it does not extend quite to the median sulcus. The second neuromeral groove is situated opposite the widest portion of the fourth ventricle. The next four are about equalh' spaced. They are very prominent in the ^-entral zone and some of them appear to reach upward a short distance into the dorsal zone. The last one is represented on the cast by a prominent mound, but the elevation does not extend as far dorsally or ventrally as do those immediately preceding it. Caudally it blends with the sulcus limitans. Bradley ('04 and '05) described seven neuromeres in a nineteen-day embryo. ^

The pontine flexure soon becomes definitely established as shown in figure 5, which is a cast from a 12-mm. embryo. In this embryo the median ventral edge of the cast is very sharp around the flexure and backward toward the spinal cord. At the pontine flexure there are six neuromeral grooves. The relation of the grooves to the median sulcus is clearly shown in the dissection, figure 7, The former seventh groove has been taken up by the sulcus limitans so that it is no longer recognizable. Above the grooves the A^entricle has become quite wide. In dorsal view the body of the ventricle slopes out laterally quite rapidly behind the isthmus, attaining its maximum width in the region of the future lateral recesses, which become distinct in embrj^os of about 15 mm.

In the 17-mm. embryo the isthmus leading from the midbrain to the body of the fourth ventricle is diamond-shaped in cross section; the ventral zones are here more extensive than the dorsal, which is the reverse of the condition in the mid-brain. The ventral median sulcus is narrow and deep, so that in the cast there is a sharp edge on the ventral surface of the fourth i^entricle extending around the pontine flexure, and onward caudally to the spinal cord. There are now five neuromeres in the hind-brain. The body of the fourth ventricle has expanded a great deal since the last stage described, and the lateral recesses are now well indicated. Slight concavities on either side of the body of the ventricle between the isthmus and the lateral recesses, in the dorsal zones, are caused by the thickening of the brain in this region to form the lateral portions of the cerebellum. Behind the lateral recesses the thin roof of the hind-brain has become deeply invaginated to form the chorioid plexus. About 100 villi are developed on the fold.

1 According to Keibel's Normentafel, pig embryos of nineteen days measure from 4.5 to 8 mm.


In a 22-nim. embryo (figs. 11 and 12) the fundamental arrangement of parts has not been altered. The cerebellar thickenings have enlarged considerably, producing correspondingly greater depressions in the dorsal zones along the body of the fourth ventricle. The sulcus limitans, for the same reason, has been made verj^ much more evident. The lateral recesses extend further to each side and are comparatively much narrower than in the younger stage considered. The chorioidal lamina extends out to the ends of the lateral recesses, and the number of villi springing from it has increased to about 150. Caudad to the chorioid plexus the dorsal part of the cavity is slightly distended or puffed up dorsally, thus forming the 'caudal protrusion' (Blake '00). In advanced embryos of dogs, cats, pigs, sheep and also the chick, according to Blake, there is a marked caudal protrusion. He wrote, This protrusion is completely closed and resembles the finger of a glove." It can hardly be described in the pig as 'finger-like' since, as shown in figure 11, it forms a rounded dome.

Taken as a whole, the fourth ventricle in the 45-mm. pig (figs. 14 and 15) has the same parts as seen in the 22-mm. embryo. The cavity of the isthmus has increased in dorso-ventral diameter from 0.75 to 0.85 mm. As seen by comparing figures 11 and 14, it has become relatively low, but laterally it has become further expanded. Its thin lateral edge, as seen in the cast (fig. 15), extends backward and becomes continuous with the body of the ventricle a short distance in front of the lateral recess. Where this thin edge fuses with the body there are three small wrinkles — the lateral remnants of the neuromeral grooves. The two halves of the cerebellum have become very much thicker and meet at an angle of about 130°. The medial part of the cerebellum is also thicker than before, so that all together the broad median fissure of younger stages has been appreciably reduced. The lateral recess, while absolutely larger than before, appears much slimmer. The floor and roof of the recess have almost come together, the cavity being largely filled with the chorioid plexus. In figure 23, in the left recess, is seen a long stretch of the chorioid fold. Sections a short distance caudad to this one show the fold to be continuous from one recess to the other. The marked villous character of the chorioid plexus is illustrated well in this section (fig. 23). It shows also the rhomboid fold projecting into the cavity of the hind-brain below the chorioidal lamina. The rhomboid fold appears in the model (fig. 15) as a sharp rim, extending along the upper part of the body of the ventricle behind the lateral recess. It extends to the caudal protrusion of the fourth ventricle, which has expanded to a very great size; its volume is more than one-half that of the remainder of the ventricle. This protrusion, from above and from behind, appears almost spherical. The posterior boundary slopes downward making almost a right angle with the narrow cavity of the caudal part of the medulla. When the body of the fourth ventricle is viewed from below, the ventral median sulcus and the two sulci limitantes are seen converging towards the cervical flexure. The ventral median groove is nearly straight and produces with the slim cavity of the cord an angle of about 125°.

In the 260-mm. embryo (figs. 25 and 26) the cavity of the isthmus is very broad and flat. On the ventral surface a deep ridge — the median ventral sulcus — is continuous with the similar ridge of the mid-brain ventricle. On account of the extensive growth of the cerebellum the dorsal surface of the body of the ventricle has become deeply concave. Only a very slight caudal protrusion is now present. Bradley ('05) described the first appearance of openings in the lateral recesses — foramina of Luschka — ^in embryos of about 100 mm. Because of these openings and on account of the growth of the chorioid plexus the cavities of the lateral recesses, as seen in the model, have been reduced to slim irregular bodies.

Measurements of the Brain

In order to show the change in the volume of the cavities during development, measurements of wax models were made by the immersion method. The results of these measurements, reduced to cubic milhmeters, are given in table 1.


Table 1. - to be formatted

Table 1.  
TABLE 1

Volume of the cerebral ventricles in cubic millimeters


EMBBYO


FOREBRAIN


THIRD VENTRICLE


LATERAL VENTRICLE


MIDBRAIN


HINDBRAIN


TOTAL CAVITY OP BRAIN


mm. 5.1


0.0948




0.022


0.206


0.3227


12


1.716


1.374


0.1712


0.357


3.38


5.453


20


7.11


2.148


2.481


2.96


3.407


13.477


24


9.893


2.357


3.768


5.181


3.57


18.644


45


30.49


4.19


13.15


6.904


5.84


43.234


260


711.58


94.6


308.4


10.07


35.5


757.15



From table 1 it is seen that each part of the entire ventricular system increases in size continually during development. The increase is relatively greater at first, and as would be expected, it becomes gradually less toward the adult. For a time — until embryos measure between 12 and 20 mm. — the fourth ventricle is the largest part of the ventricular sj^stem. After the lateral ventricles have expanded appreciably the cavity of the fore-brain is the largest part.

The cross-sectional area of the interventricular foramen was determined from wax models by measuring the area of the foramen cut through the narrowest portion.

The cross-sectional area of the interventricular foramen becomes progressively greater up to about the 12-mm. stage after which it becomes both relatively and absolutely smaller for some time. In later stages it again expands considerably; in the adult it is very much larger than in younger stages.


Table 2. - to be formatted

Table 2.  
TABLE 2 Area of the foramen interventriculare


EMBRYO


FORAMEN INTERVENTRICULARE


Length in mm.


Area in square millimeters



12


0.42



20


0.26



45


0.18



260


6.92



The mid-brain angle in early stages is very acute. For measuring the angle in the different embryos during development it is difficult to establish lines whose loci will be absolutely comparable throughout the series. The apex of the angle has been located in the middle point of the mid-brain ventricle; one line has been drawn from it to the optic recess, and the other to the middle point in the cavity of the central canal opposite the cervical bend



Fig. 1 Outline from figure 5, showing the position of the mid-brain angle


Table 3. - to be formatted

Table 3.  
TABLE 3 Increase in the mid-hrain angle


EMBRYO


MID-BRAIN ANGLE


EMBRYO


MID-BRAIN ANGLE


mm.


degrees


mm.


degrees


5.1


30.0


45


84.0


12


48.5


260


146.0


17


59.5


Adult


152.0


22


68.0


The angle increases from 30° in the 5.1-mm. embryo to 152° in the adult. The curve of growth of this angle rises up relatively rapidly at first and slowly in later stages to the adult.

Conclusions

The well-known series of models of the developing human brain made by His and the papers which they illustrate make it possible to compare the conditions which have been described in the pig with those in man. Comparisons with the embryonic brain of other mammals cannot be made, since it appears that no one has attempted to extend the work of His here referred to, or even to repeat it critically. The first impression derived from comparing His's models of the interior of the human embryonic brain with those of the pig is that they are strikingly similar, especially in the earlier stages; but more careful study shows very considerable differences. The 6.9-mm. human embryo (His, '89, Taf. 1, Fig. 2) is somewhat more advanced than the pig embryo of 5.1 mm., as indicated by the greater development of the hemisphere, and of the pontine flexure. In His's model the cavities of the parencephalon and synencephalon are not indicated and the neuromeres of the hind-brain are not shown. It may be questioned however, 'whether these structures are actually absent from the human brain at this stage. On the other hand, the model of the human brain shows a prominent tegmental fold passing from the mid-brain toward the fore-brain, but no such fold occurred in the pig embryo. In a model of a pig embryo of 5 mm. Johnston ('09) has shown the neuromeres of the fore-brain and hind-brain but there is no tegmental fold. This fold is the portion of the tegmentum which projects dorsally into the cavity of the mid-brain; the fold on either side extends from the median ventral sulcus to the sulcus limitans. Altogether Johnston's model of the brain of the 5-mm. pig agrees very closely with the first model described in the present paper, and it is evident that we have more detailed and accurate knowledge of the shape of the brain in the pig embryo than in the human embryo of corresponding stage.


His's model of the human embryo of 10.2 mm. corresponds quite closely with the pig embryo of 12 mm. and his 13.6-mm. specimen is comparable with the pig of 17 mm.; the human embryo of the third month, which completes His's series of models, is the stage intermediate between those dissected in pigs of 22 and 45 mm. In all of His's models, except the oldest, the tegmental fold is very prominent; and in the embryo of three months it is perfectly distinct. The sulcus limitans is accordingly well defined in the mid-brain, but it does not form a distinct continuous longitudinal groove from the spinal cord to the optic recess in any of His's models. In fact. His described the sulcus as becoming leveled off in the territory of the isthmus by the growth of the walls — being interrupted at the junction of the isthmus with the mid-brain.


In the casts of the ventricles of the pig, in early stages, there is a broad line of maximum width corresponding with the sulcus limitans.



Fig. 2 Sections through the hind-brain of pig embryos, {A, 3.9 mm. ; B, 10 mm. ; C, 23.6 mm.), showing the change in position of the sulcus limitans.

This groove which is lateral in the cord becomes a ventral groove in the medulla as described by His, and at the junction of the isthmus with the mid-brain it comes to an end. On account of the expansion of the roof-plate in the hind-brain the sulcus limitans soon falls below the line of maximum width. Thus in the diagram (fig. 2, B) the sulci are ventrally placed, and the width of the fourth ventricle between them is less than it is slightly further dorsally. In an older embryo (fig. 2, C) the sulci are close together and on the floor of the ventricle. In the mid-brain there is early a line of greatest width, which becomes shifted so as to form the outer border of the tegmental fold, as shown in the diagram, figure 3.



Fig. 3 Sections through the mid-brain of pig embryos, (A, 3.9 mm.; B, 23.6 mm.; C, 110 mm.); showing the change in position of the sulcus limitans.


This shifting in the mid-brain is brought about by the expansion in the dorsal zone to form the cavities in the colHcuh. The line of maximum width begins behind the constriction between the mid-brain and fore-brain in the superior collicular cavity and terminates at the caudal end of the mid-brain in the inferior collicular recess. Anteriorly the hypothalamic sulcus is seen to connect with the tegmental sulcus. This connection is most distinct in the 22. mm. embryo.

His first called attention to the dorsal and ventral zones of the brain and cord. A demarcation of the sensory from the motor portion of the central nervous system is obviously of fundamental importance and Johnston ('09) has described the sulcus limitans as the most important landmark in the brain. Diagrams have appeared which show an uninterrupted line, extending from the optic recess backward through the brain and spinal cord. However, there is no real picture which shows a sulcus continuous throughout the brain. It is distinct in each division of the brain, but at the cephalic end of the isthmus it is interrupted.

The hemisphere of course is very much larger in the human embryos than in approximately corresponding stages of the pig. The thalamus and habenular region are also further advanced in the human stages. The tegmental folds never form conspicuous projections into the ventricle of the mid-brain as they do in early human embryos. The olfactory lobe becomes progressively more conspicuous in the pig series — ^the reverse of the condition in human embiyos, of later stages especially. In the latter, the olfactory lobe is covered over by the rapidly expanding pallium. The olfactory lobe in the pig always extends some distance in front of the end of the hemisphere. The roof of the fourth ventricle is not present in aii}^ of the His models, hence there is no indication of a caudal protrusion of the fourth ventricle. This protrusion is first well indicated in pig embryos about 22 mm. long. It expands very rapidly until the cerebellum grows downward into this region. There being no foramen of Majendie in the pig, the posterior medullary velum stretches nearly straight across the caudal part of the fourth ventricle so that the caudal protrusion is just recognizable in the adult.


The form of the ventricles in the adult pig has apparently never been studied bj^ means of casts or models. Figures 25 and 26, representing the cerebral ventricles in an embryo of 260 mm., are however very similar to those which would be obtained from an adult and they ma}^ be compared with Dexler's figure of the cavity of the brain in the horse, and with any one of several figures of the ventricles in the human brain. The first of these were published by Welcker (78) who filled the ventricles with wax, injecting through the infundibulum, and published figures and a brief description of the model thus obtained. Testut ('97) figured and described a plaster cast of the ventricles. Barratt ('02) constructed a wooden model from measurements obtained from thick sections (12.5 mm.). From the method employed accuracy of detail could scarcely be expected. By far the most delicate and satisfactory' figures are those of Retzius ('00) who made casts by the use of Wood's metal. Harvey ('10) has recently used Wood's metal for the same purpose with similar results.

In the human brain immediately above the pineal body there is a backward extension of the cavity of the third ventricle which forms the supra-pineal recess. This term was introduced by Reichert ('61, Bd. 2, S. 69) who described the structure and showed its relations in median sections of the brain. In his figures the recess measures nearly 5 mm. in length. In Welcker's plaster cast it appears to be somewhat larger and in the cast by Retzius it measures 10 mm. But Testut and Harvey show onl}^ very slight protrusions. The recess may be variable in the human brain. In Dexler's model of the ventricles in the horse it is a very conspicuous object, nearly 25 mm. in length. In the adult pig it measures 5.5 mm. In proportion to the size of the third ventricle it is very much longer than in man but much shorter than in the horse. The significance of this recess has not been determined.

A very conspicuous feature of the casts of the third ventricle is the aperture made by the massa intermedia. In the several models of the human brain this aperture varies considerably in size, but in no case is it as large as in the pig or the horse. In the pig it appears to be somewhat smaller than in the horse, but in both these animals the opening is very large. The area of fusion in the 260-mm. pig measures about 8.4 sq. mm., and in the adult pig about 61.6 sq. mm.

The lateral ventricles in pig, horse and man differ very greatly. In man there is a posterior horn which is absent in the horse and pig. But the latter both show an extension of the ventricle into the olfactory lobe, whereas in man, the anterior horn ends bluntly. In the horse the pedicle of the cavity of the olfactory stalk is very long and markedly concave dorsally, it ends in an elongated irregular ventricle. The pedicle in the pig is nearly straight and much shorter. It terminates in a flattened expansion which in the anterior end is compressed dorso-ventrally.

In connection with the lateral ventricle it may be noted that its chorioid plexus in the pig is not provided with villi. Meek ('07) in his discussion of the general morphology of the plexus writes: "Villi are scarce in the chicken, duck and pigeon, but more abundant in the hog, while they reach a considerable development in the, horse, ox, and especially among porpoises, crocodiles, and some of the selachians (Pettit '02-'03)." Findlay ('99) writes similarly of this plexus: The surface of the chorioid plexus is beset with a large number of highly vascular villous projections. These are of all sizes, and the largest may branch and subdivide many times before the ultimate villi are formed." The study of the brain of the pig has shown that the chorioid plexus of the lateral ventricle first develops as an extension of the velum transversum into the lateral ventricle. The free border rapidly becomes much longer than the attached part so that it is early thrown into folds. These primary folds increase in number and give rise to secondary folds, but as shown by means of the binocular microscope, villi are not developed in this plexus.

In pig embryos of 35 to 40 mm. and in all older stages, there is a median dorsal recess behind the posterior commissure. This postcommissural recess is shown by Retzius who labels it the 'incisura postcommissuralis.' It is shown also in Harvey's lateral view. None of the other authors have an indication of it in their figures. In the adult pig the recess is very prominent.


Finally, it should be noted that the aqueduct of Sylvius remains as a distinct ventricle of the mid-brain in the adult pig. One of Retzius's figures alone gives a good lateral view of the midbrain of man. This he described as 'ventriculus mesencephali.' The cavity of the mid-brain in the horse stands out also as a distinct ventricle. In the pig the mid-brain has throughout development and in the adult a well defined ventricle which constantly increases in size as long as the brain grows.

Bibliography

Barratt, J. O. W. 1902 The form and form relations of the human cerebral ventricular cavity. Journ. Anat. and Physiol., vol. 36, pp. 106-125.

Bensley, B. a. 1910 Practical anatomy of the rabbit. Philadelphia.

Blake, J. A. 1900 The roof and lateral recesses of the fourth ventricle, considered morphologically and embryologically. Jour. Comp. Neur., vol. 10, pp. 79-108.

Bradley, O. C. 1904 Neuromeres of the rhombencephalon of the pig. Rev. Neurol, and Psych., vol. 2, pp. 625-635.

Dexler, H. 1904 Beitrage zur Kenntnis des feineren Baues der Zentralnerven systems der Ungulaten. Morphol. Jahrb., Bd., 32, s. 288-389.

FiNDLAY, J. W. 1899 The choroid plexus of the lateral ventricle of the brain. Brain, vol. 22, pp. 161-202.

Harvey, R. W. 1910 A cast of the ventricles of the human brain. Anat. Rec, vol. 4, pp. 369-384.

Herrick, C. J. 1908 The morphological subdivisions of the brain. Jour. Comp. Neur., vol. 18, pp. 393-408.

1910 The morphology of the fore-brain in Amphibia and Reptilia. Jour. Comp. Neur., vol. 20, pp. 413-547.

His, W. 1889 Die Formentwickelung des menschlichen Vorderhirns vom Ende des ersten bis zum Beginn des dritten Monats. Abh. math.-phys. Classe Kgl. Sachs. Gesellsch. Wiss. Nr. 8, Bd.'lo, S. 675-736.

1890 Die Entwickelung des menschlichen Rautenhirns vom Ende dea ersten bis zum Beginn des dritten Monats. I. Verlungertes Mark. Abh. math.-phys. Classe Kgl. Siichs. Gesellsch. Wiss., Bd. 17, S. 1-74.

1892 Zur allgemeinen Morphologie des Gehirns. Archiv. f. Anat. u. Physiol. Anat. Abt., S. 346-383.

1893 Vorschlage zur Eintheilung des Gehirns. Archiv. f. Anat. u. Physiol. Anat. Abt., S. 172-179.

1904 Die Entwicklung des menschlichen Gehirn wahrend der ersten Monate. Leipzig.

Johnston, J. B. 1909 The morphology of the fore-brain vesicle in vertebrates. Jour. Comp. Neur., vol. 19, pp. 457-539.

Keibel, F. 1897 Normentafel zur Entwicklungsgeschichte des Schweines. Jena.

VON KuPFFER, C. 1!)03 Die Moiphogenie clos Xorvensj'stems. In Oskar Hertwig's Handbueh des vorgleichenden ii. experimentellen Eutwicklungs lehre der Wirbelthiere, Bd. 2, Th. 3, S. 1-272. Jena.

Le"V\'IS, F. T. 1903 The gross anatomj' of a r2-mm. pig. Amer. Jour. .\nat., vol. 2, pp. 211-225. .


Meek, \V. J. 1907 A study of the choroid plexus. Jour. C'omp. Near., vol. 17, pp. 286-306.


MiHALKOVics, V. 1877 Entwicklungsgeschichte des Gchiriis. Leijjzig. MiNOT, C. S. 1892 Human embr3^ology. New York.

Norman, C, and Fraser, A. 1894 A ease of porencephaly. Journ. Mental Science, vol. 40, pp. 649—665.

Reichert, C. B. 1859-1861 Der Bau des Menschlichen Gehirns. Leipzig.

Retzius, G. 1900 Die Gestalt der Hirnventrikel des Menschen, nach Metallaus gussen dargestellt. Biol. Untersuch. von G. Retzius. Bd. 9. N:o. 3 u. 4. Jena.

SissoN, S. 1910 A text-book of veterinary anatomy. Philadelphia.

SMiTH, G. E. 1903 On the morphologj^ of the cerebral commissures in the verte brata, with special reference to an aberrant commissure found in the

fore-brain of certain reptiles. Trans. Linn. Soc. London. July, pp.

455-500. Testut, L. 1897 Traite d'anatomie humaine. Paris. Thompson, P. 1909 Description of a model of the brain of a foetal cat, 20 nuu. in

length. Journ. Anat. and Physiol., vol. 43, pp. 134-145. Welcker, H. 1878 Wachsausguss der Gehirnventrikel. Virchow's Archiv. f.

Pathol. Anat., Bd. 74, S. 500-503.

Explanation of Plates

Abbreviations

B.olf., bulbus olfactorius

C.pr., caudal protrusion

CbL, cerebellum

Ch.op., chiasma opticum

Coll. %., colliculus inferior

Coll.s., colliculus superior

C.inf., cornu inferius

C.par., corpus paraterminale

C.pin., corpus pineale

C.str., corpus striatum

For., foramen interventriculare

F.plx., fissure for plexus chorioideus

Hah., habenula

Hip., hippocampus

Inc.pc, incisura postcommissuralis

/., infundibulum

Is., isthmus

L.ch., lamina chorioidea epithelialis

Mes., mesencephalon

A'^i — Nt, neuromeres


N.op., nervus opticus

N^.tr., nervus trigeminus

Pa7\, parencephalon

Plx., plexus chorioideus

R.i., recessus infundibuli

R.I., recessus lateralis

R.m., recessus mamillare

R.np., recessus opticus

R.pin., recessus pinealis

R.post., recessus postopticus

R.sup., recessus suprapinealis

Rf., rhomboid fold

S.I., sulcus limitans

Syn., synencephalon

T.ch., tela chorioidea

Th., thalamus

V.b.olf., ventriculus bulbi olfactorii

V.I., ventriculus lateralis

Vel.fr., velum transversum

V.op., vesicula optica


PLATE 1

EXPLANATION OF FIGURES

4 Wax model of the cerebral ventricles of a 5.1-mm. pig. H.E.C. series 1904. X 20 diam.

5 Cast of the cerebral ventricles of a 12-mm. pig. X 15 diam.

6 Dissection of the brain of a 12-mm. pig. X 15 diam.

7 Dissection of the brain of a 12-mm. pig. X 15 diam. The plane of the cut edge of this dissection is indicated by arrows in figure 5.


PLATE 2

EXPLANATION OF FIGURES

8 Dissection of the brain of a 17-mm. pig. X 10 diam.

9 Cast of the cerebral ventricles of a 17-mm. pig X 10 diam. 10 Dissection of the brain of a 17-mm. pig. X 10 diam.


PLATE 3

EXPLANATION OP FIGURES

11 Dissection of the brain of a 22-mm. pig. X 10 diam.

12 Cast of the cerebral ventricles of a 22-mm. pig. X 10 diam.

13 Dissection of the brain of a 22-mm. pig. X 10 diam.


PLATE 4

EXPLANATION OF FIGURES

14 Dissection of the brain of a 45-mm. pig. X 6.5 diam.

15 Wax model of the cerebral ventricles of a 45-mm. pig. X 6.5 diam.

16 Left lateral ventricle of the model shown in Fig. 15.

17 Ventral view of the same ventricle.


PLATE 5

EXPLANATION OF FIGURES


18 to 23 Alicrophotographs of frontal sections through the head of a 45-mm. pig. H.E.C. series 1826. X 5 diam. The position of section 563 is indicated by arrows in figure 14.


18 Section 563.


19 Section 629.


20 Section 687.


21 Section 755.


22 Section 1067.


23 Section 1115.




PLATE 6

EXPLANATION OF FIGURES

24 Wax model of the mid-brain ventricle of a 110-mm. pig, viewed slightly from below and behind. X 15 diam.

25 Wax model of the cerebral ventricles of a 260-mm. pig. X 3 diam. 20 Ventral view of the same model.



Cite this page: Hill, M.A. (2020, February 25) Embryology Paper - The development of the cerebral ventricles in the pig (1913). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_development_of_the_cerebral_ventricles_in_the_pig_(1913)

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