ORGAN IZATIONOFREPTILES. 31 



The nervous suhstance within the cranium is subdivided into three different por- 

 tions — the medulla oblongata, the cerebellum, and cerebrum. The medulla 

 oblongata varies very much in different genera; it is prominent in Serpents, and 

 flat in the Salamanders; and in all Reptiles, the pyramids, and the restiform as 

 well as olivary bodies, are small; the latter decrease in size from the Tortoise to 

 the Siren. The cerebellum is small, slightly developed, and simple in structure; 

 it is largest in the Chelonia and Sauria, and hemispherical in form, and in all 

 wants that disposition of the white and gray substances producing the arbor vitse; 

 its colour varies a good deal — ash-coloured in Serpents, reddish-gray in the 

 Batrachia and Sauria, and deeper red in some of the Chelonia. The hemispheres 

 of the brain are always less developed than in the Mammalia or in Birds, and 

 hence the lesser degree of intelligence in these animals; the degree of intellect 

 invariably corresponding with the degree of developement of the anterior lobes of 

 the brain. In the Chelonia the hemispheres are large, oval in shape, and have a 

 ventricle or cavity within. In the Sauria the hemispheres are still larger in pro- 

 portion to the other parts; while in the Serpents they are short, very hard, and 

 terminate in a club-like olfactory nerve.* "In the Batrachia the hemispheres are 

 elongated and narrow, and in some genera, as in the Salamander, they are almost 

 cylindrical in shape; and in all Reptiles, when the hemispheres are separated, a 

 small pineal gland may be seen resting on the optic beds."t 



Nerves, are the instruments by means of which the relations of the animal are 

 carried on with the external world, for any impression made on the peripheral 

 extremity of a nerve is transmitted with incalculable velocity to the nervous centre, 

 there to produce its sensation of pain or pleasure. No sensation can be felt if the 

 free communication of a nerve with the spinal marrow and brain, be interrupted 

 by accident or design. The destruction of a nerve supplying a part is followed 

 by insensibility, if the nerve be one of sensation, and loss of locomotive power, if 



*Carus, Vergleich. Zoot. Erst. Theil., p. 508. 



t Serres, Anat. Comp. du Cerveau, torn. ii. p. 485; also Tiedemann, Anat. Comp., par 

 Jourdan, p. 242. 



