53S 



URODELA 



[CH. 



1 



Nervous 

 system. 



artery to the fore-limb on either side is given off just where the 

 systemic arch unites with its fellows to form the dorsal aorta: hence 

 it will be seen that this subclavian is of the dorsal type (p. 343). 

 Each subclavian gives off a large branch to the other breathing organ, 

 the skin, which is known as the cutaneous artery. 



It is comparatively easy to un- 

 cover the brain and 

 spinal cord of the 

 newt owing to the 

 thinness of the bones which cover 

 them. The cerebral hemispheres 

 are long and cylindrical, and devoid 

 of any other connection with one 

 another than that by way of the 

 thalamencephalon ; through the thin 

 roof of the latter two thickenings in 

 its floor, the optic thalami, can 

 be clearly seen. The mid-brain is 

 a simple smooth vesicle, and the 

 cerebellum is a slight inconspicuous 

 transverse band (Fig. 263). 



The olfactory lobe of Amphibia 

 differs from that of Chondrichthyes 

 and Gadiformes among Pisces in 

 being separated from the cerebrum 

 only by a slight constriction. From 

 its anterior end a brush of nerve 

 fibres is given off which goes to the 

 nasal sac. These constitute the ol- 

 factory nerve. The stalk connecting 

 the olfactory lobe and the cerebrum 

 is unrepresented in the Amphibia. 



The course of the cranial nerves 

 is substantially the same as in the 

 Dog-fish; owing, however, to the 

 loss of the gills and the mucous 

 canals in the adult, the branches are 



simplified. The 9th or glosso-pharyngeal, as its name implies, is 

 distributed to the pharynx and tongue. The vagus supplies the 

 larynx and glottis, but its main stem runs on to the heart and 

 stomach. 



Fm. 263. Brain of Triton, Molge 

 cristata x about 8. 



1. Olfactory nerves, representing 

 the olfactory lobes of the Dog- 

 fish. 2. Olfactory lobes. 

 3. Cerebral hemisphere. 4. Thin 

 roof of thalamencephalon. 5. 

 Optic thalami. 6. Pineal body. 

 7. Mid-brain. 8. Cerebellum. 

 9. Medulla oblongata. From 

 Burckhardt. 



