414 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 



longitudinally through the zone next the ventral surface of the 

 crescentic lamina and, on reaching the anterior commissure, bend 

 backward into the lateral wall of the aula and third ventricle; 

 a certain number of fornix fibers cross over in the posterior border 

 of the lamina terminalis and produce the commissura hippocampi. 

 The corpus callosum is formed in the dorsal zone of the crescentic 

 lamina terminalis. 



The corpus callosum (Fig. 121) is produced by fibers that 

 grow from one cerebral hemisphere to the other through the fronto- 



ptc 



Fig. 123. Permanent fissures and sulci on the convex surface of the cerebrum 

 as seen in a seven months embryo. (McMurrich after Cunningham.} 



is. Superior frontal fissure, ip. Interparietal. IR. Island (Reili). pci. Inferior pre-central. 

 PCS. Superior pre-central. ptc. Post-central. R. Central (Rolandi). S. Lateral (Sylvii). 

 t l . First temporal. 



dorsal zone of the lamina terminalis. The different parts of the 

 corpus callosum are formed in regular order rostrum, genu, 

 truncus, splenium and this order coincides with the lines of 

 growth in successive stages of cerebral development. The fibers 

 of the corpus callosum pierce the dentate gyrus of the hemisphere 

 vesicle. In so doing, they completely obliterate the superior part 

 of the hippocampus and leave but rudiments of the dentate gyrus, 

 namely, the gyrus supracallosus and gyrus subcallosus (longitu- 

 dinal striae and peduncle of the corpus callosum), the fasciola 



