RELATIVE WEIGHT AND VOLUME OF COMPONENT PARTS OF FETAL BRAIN. 55 



has declined to 5.2 grams or 1.03 per cent, which 

 is the lowest mark in the weight-curve for this 

 complex. Of this the olfactory bulb con- 

 tributed 0.2 per cent, and the paraterminal body, 

 fornix, and hippocampus, 0.83 per cent. The 

 mesencephalon likewise reaches its 'owest relative 

 level at this stage, weighing but 0.64 per cent of 

 the total weight of the encephalon. The rhom- 

 bencephalon weighed 35.28 grams, or 6.98 per 

 cent, the medulla-pons weighing 4.58 grams 



H e o p : 



(0.91 per cent) and the cerebellum 30.7 

 grams (6.07 per cent). This represents for 

 the former the lowest point in the series, and for 

 the latter a marked gain over preceding figures. 

 In this specimen the total brain constituted 

 15.75 per cent of the body-weight, a somewhat 

 greater proportion than is usually reported. 

 Jackson (1909) gives 14.6 per cent and Vierordt 

 (1893) 12.29 per cent. 



N eo 



' P , 



10 



Hypothal. 



Parat body 

 ( pillar fornij!) 



Olfact 8 



FIG. 10. Mesial view of right half of telencephalon of embryo shown in fig. 9. X 2. 

 Flo. 11. Mesial view of the subdivided archipallium of embryo shown in figs. 9 and 10. X 2. 

 FIG. 12. Drawing of a homisection of brain shown in figs. 9, 10, and 11, with subdivisions of basal 

 ganglia outlined. (Section b, slide 145.1 X 2. 



BRAIN VOLUME AT DIFFERENT STAGES. 



Since we have the volume of the models of the brain and its separate parts for 

 the different stages of development, it is possible to roughly calculate the actual 

 volume by dividing the model volume by the cube of the magnification used for the 

 reconstruction. It must be borne in mind, however, that since we are dealing with 

 brains that have been embedded in paraffine or cel- 

 loidin, the models represent the embedded brain and 

 one must take into account a considerable shrinkage 

 of the tissues. The shrinkage of a given brain is 

 more or less uniform throughout and therefore, in 

 itself, does not interfere with the determination 

 of the relative volume of its different parts. As 

 regards the actual volume, however, one must 

 take into consideration the primary swelling of 

 the brain when placed in a formalin solution and 

 its subsequent shrinkage in the course of its 

 preparation into serial sections. From our own 

 experience and that of others we can estimate 



TABLE 2. Volume of brain at different 

 stages of development, calculated by 

 dividing the model volume by the cube 

 of its magnification. 



