CoGHiLL, Cranial Nerves of Amblystoma. 28 1 



V. The First Two Spinal Nerves. 

 /. — The Motor Component. 



In Salamandra, Menopoma and Triton Drcner finds spino- 

 occipital nerves which arise within the cranium and unite with 

 the ventral ramus of the first spinal nerve. These nerves are 

 especially strong in Triton. Here they arise from the ventral 

 side of the medulla caudally of the exit of the most caudal 

 vagus root, in line with the ventral roots of the spinal nerves. 

 A small branch passes dorsally of the ganglion IX+X to the 

 dorsal muscles. The larger division passes through a distinct 

 foramen beneath the occipital condyle and passes ventrally of 

 the musculature to fuse with the ventral ramus of the first 

 spinal nerve near the flexure of the latter cephalad. 



Druner does not find these nerves in Menobranchus and 

 reports their occurrence in Proteus as doubtful. They do not 

 occur in Amblystoma. On the other hand, instead of nerves 

 from the region of the vagus to that of the first spinal, a 

 branch from the first spinal passes cephalad across the dorsal 

 surface of the ganglion IX+X to the musculature of that 

 region. 



With the exception of the occurrence of spino-occipital 

 nerves in some species, the hypoglossal nerve in all Urodela 

 seems to be formed as in Amblystoma by the fusion of the 

 ventral, motor rami of the first two spinal nerves. 



2. — TJie Cutaneous Component. 



Ganglia are not found on the dorsal roots of the first two 

 spinal nerves in all Urodela. Druner finds a ganglion upon 

 the root of the first spinal in larvae of Salamandra, and occa- 

 sionally in the adult also. It is not so frequently found in 

 larvae of Triton, and never in the adult. Neither is it found in 

 Proteus and Menobranchus. In Proteus and Menobranchus, 

 also, no ganglion is found on the root of the second spinal 

 nerve. Amolystoma agrees closely with Salamandra and Tri- 

 ton in this respect, since the ganglion is well developed on the 

 root of the first spinal nerve, and of variable occurrence on the 

 root of the second. 



