294 



Vcterinarv Obstetrics 



hemispheres grow rapidly and the walls of the skull fail to close 

 over them, so that they protrude, to constitute hcniia cerebri, as 

 shown in Fig. 32. 



From these cerebral hemispheres, there grow out early in their 

 development the olfactory vesicles, which are later to develop 

 into the olfactory lobes, from which the olfactory nerves pass to 

 the nose. These .sometimes fail to appear if the optic vesicles are 

 represented by a single vesicle, to constitute a cyclopean monstros- 

 ity as shown in Figs. 29 and 30. 



Fig. 32. Herni.-v Cicrebri. Pig. 



Lateral view of brain, seen from the left. 



A, Segment of .skin covering theherniate<1 portion of the brain, B. 



CC, Cerebrum. D, Cerebellum. E, Medulla oblongata. 



Thp: Spinal Cord. 



As already suggested, the spinal cord develops from the pos- 

 terior portion of the neural groove. The neural folds grow up- 

 ward and their borders approach each other, to finally fuse at 

 their margins, leaving a cavity within, which constitutes the 

 central cavity of the spinal cord, and persists throughout the 

 life of the animal. The neural canal is lined by columnar, cili- 

 ated epithelium which persists throughout life, to constitute the 

 epithelium of the central canal. The deeper layers of epithe- 



