TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 121 



Siren lacertina, and in general accord with the arrangement 

 characteristic of urodeles (Coghill, '02, '06; Driiner, '01, '03; 

 KalHus, '01, and Norris, '13). The ventral rami of the first and 

 second spinal nerves, tj^pically, unite to form the hypoglossal 

 trunk which supplies the hypobranchial musculature. In 

 Amphiuma, however, Norris ('08) described the hypoglossal 

 trunk as being derived solely from the ventral ramus of the first 

 spinal nerve. A resume of the arrangement of the hypoglossal 

 complex in both anurans and urodeles is given by Black ('17). 



In Amblystoma punctatum the first spinal nerve is entirely 

 motor. It divides into dorsal and ventral rami. The latter at 

 first passes caudolaterally through the dorsal axial musculature 

 to the lateral border of the pharynx. Then it curves laterally 

 and ventrally around the pharynx, and at a point just caudal to 

 where the ramus intestino-accessorius X breaks up into its 

 component divisions, it unites with the anterior prolongation of 

 the ventral division of the second spinal nerve. The common 

 trunk thus formed (hypoglossal), after contributing a branch to 

 the ramus intestino-accessorius X, passes anteriorly along the 

 dorsolateral border of the ventrolateral musculature beneath 

 the pharynx. More anteriorly, it runs slightly lateral to this 

 muscle mass and supplies its component segments (m. sterno- 

 hyoideus). The distal anterior prolongation of the nerve enters 

 the substance of the m. geniohyoideus, in which it travels for a 

 considerable distance, giving off branches. The terminal por- 

 tion emerges from the m. geniohyoideus and finally breaks up 

 in the m. genioglossus. 



The second spinal nerve arises by both dorsal and ventral roots 

 and presents a small ganghon. The proximal part of the ventral 

 ramus passes posteriorly for a short distance through the longi- 

 tudinal trunk musculature, then passes laterally to the dorso- 

 mesial border of the ventrolateral musculature. Here it curves 

 anteriorly, and after supplying motor fibers to the ventrolateral 

 musculature, it unites with the first spinal nerve. According to 

 Norris ('13), the ventral ramus of the second spinal nerve in 

 Siren contributes a branch to the brachial plexus which in this 

 form is made up principally from the third and fourth spinal 



