600 



DEVELOPMENT OF FffiTAL BRAIN. 



for the first time the corpus oUvare, consisting chiefly of a mass 

 of granular matter. 



— Each lobe of the cerebellum is about an inch in breadth. 

 The hemispheres of the cerebrum have increased greatly in size 

 in proportion to the growth of the cerebellum and medulla. 

 They are extended even posteriorly to the cerebellum and are 



Fig. 227.* 



about two inches in length. On their upper surface the convo- 

 lutions have now become apparent ; but the walls are still very 

 thin, compared with the great size of the ventricles. The nates 

 and testes are conspicuous on the masses of the tubercula quad- 

 rio'emina, and in front of the eminentiae mammillares is seen the 

 pituitary gland. 



— On opening the ventricles, the corpus callosum is found 

 developed backwards to its full extent, and enveloped in part 

 by a plane of fibres that comes from the outer side of the corpus 

 striatum and the thalamus. On the outer side of this plane and 

 in contact with it, another diverging layer which belongs to the 

 cerebral hemispheres passes up as an expansion from the crura 

 cerebri through the corpus striatum and the thalamus ; the fibres 



* Left hemisphere of the brain with the radiation of the fibres seen after the 

 removal of the top portion of the cerebrum in a foetus of six months, a. Point 

 of radiation ; within, at this point but not seen, is the corpus striatum, b, b, b, b. 

 Fibres of the crus cerebri which radiate forward, bacliward and outward, c. 

 The radiating fibres of the periphery which cover on their outer face the pre- 

 ceding, and are overlaid themselves on the exterior with a soft granular cover- 

 ing, d. Fissure of Sylvius. 



