54 RELATIVE WEIGHT AND VOLUME OF COMPONENT PARTS OF FETAL BRAIN. 



telencephalon weighing 88.78 per cent. Of the 

 latter the neopallium comprises 78.82 per cent 

 and the corpus striatum 7.62 per cent, the former 

 an increase, the latter a decrease as compared 

 with the preceding stage. The archipallium has 

 declined to 2.34 per cent, the olfactory bulb 

 weighing 0.14 per cent, the paraterminal body, 

 fornix, and hippocampus 2.2 per cent, the lowest 

 point yet reached by these parts. Themesenceph- 





-VOIfacI B. 



; \_Para'erm.B. 



, basal qangli 



' Dienceph. 



Mesenceph . 

 Cerebel. 







; 



Pons Medulla 



FIG. 9. Ventral view of a reconstruction of brain of embryo No. 

 1400-28, 150 mm. crown-rump length, showing manner in 

 which it was subdivided. X 2. 



alon has also decreased, constituting but 1.44 

 per cent of the encephalon. The total rhomb- 

 encephalon weighs 4.97 per cent, slightly below 

 that of the 119 mm. specimen, the loss being 

 sustained by the meclulla-pons which now weighs 

 2.23 per cent, while the cerebellum weighs 2.74 

 per cent, the same weight-ratio as that in the 

 ' preceding stage and virtually the same as that in 

 the 80 mm. stage. This structure thus main- 

 tains a relative weight-level extending over a 

 period of six weeks, which really means that there 

 has been an acceleration of growth during this 

 interval. The foregoing specimens were all 

 modeled and the models separated into these 

 various parts for study. 



Fetus 230 mm., estimated age 26 weeks. 



This stage is represented by a fetus of which 

 only the brain was available for study. Since 

 the specimen had readied a sufficiently advanced 

 state of development to permit the removal and 

 dissection of the brain, the actual weights and 

 volumes can be given. In form and fissures this 

 brain corresponds to a stage between the two 

 shown by Retzius (189G, plate 14, figures 3, 4, 5, 



and figures 6, 7, 8), and has therefore been 

 placed at 340 mm. total length, or 230 mm. crown- 

 rump length, and its age estimated as 26 weeks. 

 These data were obtained from Dr. Streeter, who 

 dissected and studied the specimen. 



The total prosencephalon weighed 93.32 per 

 cent of the encephalon, a fractional loss as com- 

 pared with the 156 mm. fetus. Of this the clien- 

 cephalon constituted 3.7 per cent, less than the 

 preceding one. The telencephalon, the total 

 weight of which wa 89.62 per cent, was sub- 

 divided into th neopallium, weighing 79.21 

 per cent, and (he corpus striatum, weighing 

 8.33 per cent, both showing an increase. The 

 archipallium weighed but 2.08 per cent, the 

 lowest point yet reached. To this the olfac- 

 j tory bulb contributed 0.13 per cent, the para- 

 terminal body, fornix, and hippocampus, 1.95 

 per cent. The mesencephalon weigljed 1.42 

 per cent, practically the same as in the preced- 

 ing specimen. The total rhombencephalon 

 weighed 5.26 per cent, a somewhat greater 

 relative weight than at 19 weeks. This added 

 amount was contributed by, the cerebellum, 

 which weighed 3.15 per cent, as compared 

 with a medulla-pons weight of 2.11 per cent, 

 which is only a small fraction less than in 

 Dockeray's fetus, the last and largest of the 

 modeled specimens. 



No. 2558, 367 mm., new-born white male. 



This specimen had been injected and pre- 

 served in 10 per cent formalin. The sitting 

 height was 367 mm., body-weight 3,210 grams. 

 The head measurements were as follows: 

 length 130 mm., width 102 mm., circumfer- 

 ence 381 mm., biaural arc 248 mm. The brain 

 was removed by Dr. A. H. Schultz, of the Car- 

 negie Embryological Laboratory, to whom I am 

 indebted for the foregoing data. Judging from 

 macroscopic appearance, both body and brain 

 were normal and well developed. The enceph- 

 alon weighed 505.61 grams; the actual volume, 

 as determined by water displacement in a large 

 graduated cylinder where the indices could be 

 easily read, was 489.97 c. c. The cerebral 

 hemispheres were very large, richly convoluted, 

 and had thickened until the cavity of the lat- 

 eral ventricle was reduced to a mere slit. The 

 total prosencephalon weighed 467.12 grams, or 

 92.38 per cent of the whole brain, slightly 

 less than that of the preceding. Of this the 

 diencephalon contributed 2.63 per cent, a loss 

 of about 30 per cent as compared with the 

 230 mm. fetus. The telencephalon weighed 

 89.75 per cent of the whole, maintaining the 

 same weight-value as the preceding specimen. 

 Of this the neopallium weighed 424.3 grams, 

 or 83.92 per cent, and the corpus striatum 

 24.3 grams, or 4.8 per cent, a considerable 

 relative gain for the former. The archipallium 



