548 H. W. NORRIS AND SALLY P. HUGHES 



branches of the first and second spmal nerves, runs anteroven- 

 trally, shghtly lateral to the wall of the pharynx, just ventral to 

 the ventral border of the levator arcuum branchialiuni muscle. 

 At about the level of the exit of the third spinal nerve the cu- 

 taneous component of this first and second spinal nerve deriva- 

 tive leaves as a dorsal branch (fig. 39, sp.'2) which soon curves 

 ventrally and laterally, and descends through the interval be- 

 tween the sphincter colli muscle laterally and the rectus abdomi- 

 nis muscle medially, finally passing through the former muscle 

 ffig. 38) to be distributed laterally and ventrally to the skin in 

 the posterior head and anterior trunk region. 



The remaining motor constituent forms the nervus hypoglos- 

 sus (fig. 39, sp.l = JigL). Just before and shortly after the sepa- 

 ration of the cutaneous element small motor branches are given 

 off which run to the ventral portion of the rectus abdominis 

 musculature at the level of the fourth spinal nerve. The 

 main trunk of the hypoglossus passes anteriorly at the 

 lateral border of the thoracicohyoideus division of the ven- 

 tral rectus abdominis muscle. It enters the latter muscle (fig. 

 38), gives off some small branches and then divides into a smaller 

 dorsolateral and a larger ventromedial division, the former sup- 

 plying the hypoglossus and the lateral portion of the geniohyoideus 

 muscle and the latter the deeper medial portion of the thoracico- 

 hyoideus muscle and the geniohyoideus also (figs. 34-32, 25-20). 



In Herpele the hypoglossus is thus formed from the first spinal 

 nerve only. This is the characteristic origin of the nerve in the 

 Amphibia. In Amphiuma the senior writer ('08) found in the 

 hypoglossus only the first spinal nerve represented, Druner and 

 others to the contrary. In Siren, as in Herpele, there is a union 

 of branches of the first and second spinal nerves, but as motor 

 and sensory branches are given off from the combination before 

 the hypoglossus proper is reached, it is probable that only first 

 spinal fibers remain in it. In Spelerpes Bowers ('00) believed 

 the hypoglossus to be derived from the second spinal nerve. 

 The writer finds that it is the first spinal nerve in Spelerpes that 

 forms the hypoglossus. In Necturus, however, the hypoglossus 

 is formed from the first and second spinal nerves. 



