MOTOR NUCLEI IN PHYLOGENY 399 



rate foramen below the occipital condyle and fuses ventrally 

 with the ventral ramus of the first spinal nerve. Spino-occipital 

 nerves were also observed by this author in Menopoma (Crypto- 

 branchus alleganiensis) and Salamandra. Fiirbringer (21) noted 

 a similar condition in a specimen of Cryptobranchus japonicus, 

 though according to this author spino-occipital nerves are not 

 commonly present in adult urodeles. With the exception of 

 the occurrence of a spino-occipital nerve in some species, Cog- 

 hill concluded that the formation of the hypoglossal nerve by 

 the junction of the ventral motor rami of the ^rst two spinal 

 nerves, is the usual arrangement among urodeles (16). 



In Siren lacertina (Norris, 46) the ventral ramus of the first 

 spinal nerve joins that of the second spinal nerve to form the 

 hypoglossal trunk. The latter nerve is distributed posteriorly 

 to the three anterior segments of the m. abdomiuo-hyoideus, to 

 the m. sterno-hyoideus and to the m. omo-hyoideus. Ante- 

 riorly the nerve innervates the m. genio-hyoideus. No genio- 

 glossus muscle was found in Siren and no mention is made of a 

 m. hyo-glossus. A branch from the ventral ramus oi the 

 second spinal nerve to the brachial plexus is described. 



From this short summary it appears that the hypoglossal 

 trunk is formed in much the same way in each of the urodeles 

 described, though in the case of Amphiuma, Norris (45) notes 

 that the hypoglossal nerve is formed entirely by the ventral 

 ramus of the first spinal nerve. On the other hand, the hypo- 

 glossal trunk in anurans is derived solely from the ventral 

 ramus of the second spinal nerve. 



Whether the amphibian hypoglossus is formed by the ventral 

 ramus of the first spinal nerve alone, by the union of this trunk 

 with that of the second spinal nerve or only by the ventral 

 ramus ol the second spinal nerve, the plan of peripheral distri- 

 bution is very similar in all cases and the musculature which it 

 innervates is represented with but few exceptions in both 

 urodeles and anurans. 



Thus, the differentiation of a circumscribed dorso-medial 

 nucleus in the rostral end of the somatic motor column of the 

 cord in opisthoglossal anurans cannot be due to the possession 



