REPTILIA. 



311 



hemisphere, and projecting considerably into 

 the lateral ventricle. The furrow which se- 

 parates the bigeminal bodies is not so deep 

 in the Saurians as in the Chelonian order. 

 The cerebellum is very small, being repre- 

 sented by a transverse layer of nervous sub- 

 stance. In the Ophidian reptiles the two 

 hemispheres form together a mass which is 

 broader than it is long ; the olfactory bulb is 

 frequently of very large size, as, for example, 

 in the Python (fig. 225) ; the corpus striatum 

 is much smaller than in the Saurians. In the 

 Python it is divided. The bigeminal tubercles 

 are almost globular in many species, and 

 much smaller than the hemispheres behind 

 which they are situated. In the Python they 

 are remarkable, inasmuch that they are four 

 in number, and closely resemble the corpora 

 quadrigemina of mammalia. 



The cerebellum of serpents (fig. 225, c.) is 

 exceedingly small and flattened ; it has the 

 shape either of the segment of a circle or of 

 a thin quadrilateral lamina, which partially 

 covers the fourth ventricle. 



In reptiles, as in birds, the medulla spinalis 

 is permeated by a canal, which is lined inter- 

 nally with grey substance. In the Saurian and 

 Ophidian reptiles this canal extends as far as 

 the first coccygeal, but in the Chelonians it is 

 shorter. 



The origin of the nerves derived from the 

 encephalon and spinal chord closely resembles 

 what is met with in the higher vertebrata: 

 their general distribution will be best under- 

 stood by referring to the explanations ap- 

 pended to the annexed figures, copied from 

 Mr. Swan's elaborate work on the Compara- 

 tive Anatomy of the Nervous System. 



Fig. 226. 



Nerves of Boa Constrictor. (After Swan.") 

 1, ganglion of the sympathetic nerve, situated 

 near to, and connected" with, the trunk of the par 

 vagum. 2, a branch of the sympathetic nerve 

 passing some way in a canal at the base of the 

 cranium, and forming a small ganglion with a 

 branch of the second trunk of the fifth ; it sends 

 filaments to the membrane covering the posterior 

 part of the mouth and palate, one of which com- 

 municates again with the second trunk of the fifth 



before its termination; the ganglion then sends 

 another branch forward to form another glanglionic 

 union with a branch of the second trunk of the fifth, 

 and from this a branch is sent to the posterior part 

 of the nose to ramify on the schneiderian mem- 

 brane ; other branches are given to the membrane 

 covering the mouth and palate, and one passes for- 

 ward and communicates again with a branch of the 

 second trunk of the fifth, and is distributed on the 

 membrane covering the anterior part of the mouth 



x 4 



