XERVOVS SYSTEM. 



still disposed on the same plain, and in a longitudinal direc- 

 tion, as we find them in the adult fishes and in the embryos 

 of mammalia. They incline forwards as they develope up- 

 wards and backwards and laterally, and in the adult condition 

 the optic lobes, reduced in their proportion and forced down- 

 wards and to the sides, are covered by the expanded cerebral 

 hemispheres, which reach and even partially overspread the 

 cerebellum. The spinal chord still extends into the coccy- 

 geal vertebrae, and the decussating bands of the corpora py- 

 ramidalia are more numerous and distinct than in the inferior 

 vertebrata, as seen in the medulla oblongata of the stork, 

 (Fig, 98. A. k.) The cylindrical spinal chord (98. A. ,) per- 

 forated by a small canal dilates on entering the cranium into 



FIG. 98. 



a wide and large medulla oblangata (98. A. b,) which is not 

 yet traversed by a cerebellic commissure, or pons Varolii. 

 The large cerebellum covers the fourth ventricle, which is 

 ext3nded into it, as seen in the cassowary, (Fig. 98. B. d,f,) 

 it consists of the vermiform or median lobe (98. B. d,) and a 

 small rudiment of the lateral lobes or hemispheres (98. A. /,) 

 and it is deeply sulcated transversely on the exterior, like the 

 cerebellic hemispheres of mammalia. The numerous me- 



