THE BRAIN. 



413 



sensory fibers ascend through the striated body to the cortex from 

 the thalamus and other ganglia. All these motor and sensory 

 fibers together constitute the internal capsule. Its bell-shape in 

 the hemisphere is due to the rotary growth of the hemisphere, 

 upward, backward, downward and forward, around the corpus 

 striatum (Figs. 32 and 33). 



Anterior Commissure (Fig. 121). The lamina terminalis 

 at the fourth week is a thin median plate bounding the aula an- 

 teriorly and joining the hemisphere vesicles together just in front 

 of the foramina interventricularia (Monroi) (Fig. 17). Its ven- 

 tral portion remains thin; but its dorsal part thickens greatly and, 



Fig. 122. The fossa lateralis cerebri, in embryonic brain of the fourth month. 

 (After McMurrich.) 



c. Cerebellum, p. Pons. 5. Fossa lateralis cerebri. 



with the upward and backward growth of the hemisphere, it is 

 extended in a crescent, dorsal to the interventricular foramen, 

 as far backward as the splenium of the corpus callosum. Within 

 this thickened crescentic part of the lamina terminalis are formed 

 the anterior commissure, the body of the fornix, the corpus callo- 

 sum and the septum pellucidum. The anterior commissure is 

 first formed. Through the ventral angle of the thickened por- 

 tion grow, transversely, the commissural and the decussating 

 fibers of the rhinencephalon and the commissural fibers connect- 

 ing the occipito-temporal cortices. These fibers make up the 

 anterior commissure. The fornix fibers grow for the most part 



