CONSIDERATIONS OF THE BRAIN OR ENCEPHALON. 



35 



calvaria. Only the great convoluted hemispheres of the cerebrum 

 are visible from the superior view-point. The two hemispheres 

 are separated by a deep, median cleft, called the longitudinal 

 fissure of the cerebrum (fissura longitudinalis cerebri) from 

 which the falx cerebri has been removed. 



Posterior View. When the brain is viewed from behind, three 

 great structures and two transverse fissures are visible (Fig. 20): 



Fig. 1 6. Diagrams of surface views and sections of germinal areas showing 

 the development of the primitive streak, neural groove, neural tube and brain 

 vesicles. (After Morris's Anatomy.) 



A. Earlier stage, a. Germinal area. b. Neural groove, c. Primitive streak. B. .Later 

 stage, a. Germinal area. b. Fore-brain (rudiment of cerebral hemispheres), c. Optic vesicle. 

 d. First cerebral vesicle, e. Second cerebral vesicle, f . Third cerebral vesicle, g. Primitive 

 streak. A'. Section through area A along the line a. a. Germinal area. b. Neural groove. 

 B'. Section through area B along line b. a. Germinal area. b. Neural crest, c. Neural tube. 



First, the occipital end of the cerebral hemispheres with their 

 irregular gyri and sulci; second, the transversely laminated cere- 

 bellum, lying below the cerebrum and separated from it by the 

 transverse fissure of the cerebrum (fissura transversa cerebri); 

 and third, the inferior extremity of a relatively small median 

 structure, the medulla oblongata. The cerebellum is especially 



