Volumetric determinations of the parts of the brain in a human fetus 156 mm. long (crown-rump)код для вставкиСкачать
VOLUMETRIC DETERMINATIONS OF THE PARTS O F THE BRAIN I N A HUMAN FETUS 156 MM. LONG (CROWN-RUMP) F. C. DOCKERAY Department of Psychology, University of Kansas I n the present communication there is reported a study of the volume of the main divisions of t,he brain as they are found in a fetus about four months old. The work was undertaken as a step in the history of the growth of the individual parts of the brain under the premise that a knowledge of their volume priority would indicate in a general way the functional priority of these parts. By means of the wax-plate reconstruction method it is possible to make an accurate enlarged model of the brain that can be separated into its chief component parts. Since such a model is made of wax of a uniform composition the relation by volume and by weight of the different parts can be determined both as to each other and as to the brain as a whole. This same method was used in determining the volume of the different parts of the opossum brain, by Professor Streeter and by Mr. H. A. Tash, who reported their results at the meeting of the American Association of Anatomists at 1thaca.I The brain measured was taken from a male fetus measuring 156 mm. crown-rump, and 201 mm. total, length. The head measurements were: Bitemporal, 48 mm. ; occipito-frontal, 58 mm. These measurements were made on the fresh specimen. Its weight was 296 grams. The specimen was preserved in 10 per cent formalin, the skull having been opened to facilitate the penetration of the fixative. Subsequently the brain was removed, embedded in celloidin and prepared in serial sections 50 p thick, 1 Streeter, G. L., 1911, Volumetric analysis of the brain of the opossum. Proc. Amer. Assoc. Anat.; Anat. Rec., vol. 5 , p. 91. 207 THE ANATOYICAL R E C O R D , VOL. 9, N O . 2 208 F. C. DOCKERAY every other section saved and stained with alum-cochineal. From this series a model was made enlarged five diameters after the well known Born method. Serial drawings were made with n projection apparatus on papers which were then incorporated in wax plates of such a thickness that the enlargement in all plmes was the same ( x 5). The drawings were then cut out from the plates and filed. This gave a model of the whole brain with the ventricles removed.. The plates were then gone through n second time and the various parts cut away from each other so that their individual weights and volumes could be separately determined. It was found that this could be done with considera,ble accuracy, and having the stained sections as a guide, it would have been possible to have carried the subdivisions further. But, having in mind both younger and older stages, it was decided that the adopted subdivision would prove most practical in the end. The results are given in table 1. I n the first column of the table is given the weight in grams of the whole model and of its parts. In the second column is given the percentage of the total weight formed by each part, which would hold true for TABLE 1 - MODEL WGT. I S GMR. I ' PARTS . ~~ .. PER CENT O F TOTAL WGT. Ilhombencephalon. , . . . . . . . . . Medulla and pons.. . . . . . . . . . .' Cerebellum.. . . . , . . . . . . . . . . . . Mesencephalon. . . . . . . . . . . . . .; Dicncephalon (inc. epiphysis) Telencephalon. . . . . . . . . . . Basal ganglia. . . . . . . . . . . . Caudate nucleus (inc. parolf.. body and amygdaloid nu- 72,135 32.325 39.810 20.900 69.761 4.973 2.228 2.744 1.441 4 .so9 88.776 7.625 . . . . . . .. : 73.150 33.161 4.299 33.865 26.075 5.815 5.043 2.286 0.296 2.334 1.797 0.401 0.136 78.815 100.000 , . . . . . . .' Gtobus pallidus.. , . . , . . . . . . . . i Archipallium. . , . , . . . . . . . . . . . Fornix and hippocampus.. . . . Paraterminal body.. . . . . . . . . . ' Olfactory bulbs.. . Seopallium.. . . . . . , . . . . . . , , , . 1143.198 Total brain.. . . . . . . . . . . . . . . . . 1450.468 MODEL VOL. I N CC. -. ACTD AI. VOLUME -_ _ ~ _ -~ ___~ 80.565 36.500 44 ,065 23.659 78.970 1457 ,658 125.210 0 644 0 292 0 352 0 189 0 631 11 661 1 001 82.805 37 ,538 4.867 38.341 , 29.522 6.583 , 2.236 , uY4.1Uu 1641.929 I 1 0 662 0 300 0 039 0.306 & : ; 0.017 lU.64D 13.135 BRAIN OF A HUMAN FETUS 209 the actual brain just as for the model. In the third column is given the volume in cubic centimeters of the whole model and of its different parts. Instead of determining the volume of each part separately it was found more practical to determine the specific gravity of the wax plates and then calculate the volumes from the weights given in the first column. In the last column is given the volume of the brain itself and of its parts. This was obtained by dividing the volume of the model by the amount of the enlargement, i.e., the cube of five diameters. It is to be remembered that this is the volume of the brain after it has been embedded and prepared in serial sections. The volume of the fresh brain could be obtained only by calculating the amount of shrinkage the specimen experienced in this process. The subdivisions that were used follow as far as possible the embryological subdivisions adopted by His. Their boundaries could in most cases be determined by the cell structure of the sections. In some cases it was necessary to depend on the surface configuration of the model. The landmarks utilized in carrying out this subdivision are herewith detailed : Rhombencephalon. This was separated from the spinal cord as nearly as possible at a point post cephalic to the first cervical nerve. The cephalic boundary was determined by a plane just skirting the inferior colliculus and passing out ventrally just in front of the pons. Laterally this plane passes just in front of the brachium connecting the cerebellum and pons. Cerebellum. This is plainly demarcated by its surface outline, while the pons is determined more by its internal structure, the main characteristic being the densely massed nuclei. The cerebellum at this time consists of a well fissured vermis and the two lateral lobes which are fissured dorsally but are still smooth ventrally. In removing it the floccular margin was included and also the brachium pontis on each side to the point at which it meets the pons. The removal of the Cerebellum leaves the medulla and pons, whose weight and volume are given together. Mesencephalon. The caudal limit of the mesencephalon is the same as the plane marking the cephalic border of the rhombencephalon, which has already been given. Its cephalic limit is a 210 F. C. DOCKERAY wedge-shaped plane that projects in between the masses of the diencephalon. At the median line its boundary is marked dorsally by the posterior commissure and ventrally by a point post caudal to the mammilary bodies. From this median line the plane of division on each side extends backward so as to include the red nucleus with the midbrain and comes to the surface a t a groove marking the antero-lateral margin of the superior colliculus. Owing to the advanced development of the colliculi and the retarded development of the peduncular portion, the mesencephalon is V-shaped as regards its ventral aspect, as well as its cephalic boundary. Diencephalon. Its separation from the mesencephalon we have already indicated. From the telencephalon it is separated bilaterally by the internal capsule, and a sharp line of demarcation on the surface is afforded by the stria terminalis. Ventrally where this is not present the line of division is continued along the anterior margin of the optic tract. By this manner of subdivision there is comprised in this portion the optic tract and thalamus including the habenular nuclei and epiphysis and also the whole hypothalamus with the exception of the hypophysis, which had been removed. Telencephalon. This includes all the remainder of the brain. It was subdivided into three main divisions as follows: Basai ganglia. At the end of the fourth month these structures are clearly defined and bear a relation that closely approxjmates the adult. The putamen and globus pallidus are easily recognized in transverse sections. As for the lamina of capsule fibers that surround them, the incisions were made half-way, so that part of the fibers would go with the globus pallidus and part with the caudate nucleus. The caudate nucleus throughout its greater extent is likewise clearly defined. At its head and tail ends, however, it is complicated by fusing with the parolfactory body and amygdaloid nucleus respectively. On this account these latter were included with it. Archipallium. This includes, in the first place, the olfactory bulbs, which were removed at a transverse line at the point where BRAIN OF A HUMAN FETUS 211 they become free from the brain wall. This corresponds to both the bulb and stalk of the adult. The paraterminal body includes the gray substance where the olfactory bulb is attached and the region of the future septum pallucidum and the pillar of the fornix, which could not be easily separated from it. The remainder of the archipallium is made up of the body of the fornix and its fimbricated extension into the hippocampus. The hippocampus is easily recognized by its histological structure and by the way it bulges into the lateral ventricle. With i t was included the dentate fascia and the uncinate body. The corpus callosuin was included with the neopallium. Neopallium. This includes the remainder of the telencephalon and represents what we know in the adult as the convoluted cortex, together with the subjacent white matter and includes the corpus callosum, as we have just pointed out. I n conclusion I wish to acknowledge the courtesy of Professor Streeter, who kindly put the resources of the Anatomical Laboratory of the University of Michigan at my disposal for the purpose of this investigation, and gave me many helpful suggestions as the work progressed.