IOWA ACADEMY OF SCIENCE 141 



laris a truncus hyomandibularis can hardly be said to occur. In Neeturus 

 the r. jugularis passes out exteriorly dorsal to the squamoso-eolumellar 

 ligament and the dorso-lateral border of the cephalo-mandibular por- 

 tion of the depressor mandibular muscle. In Spelerpes the r. jugu- 

 laris passes out through the cephalo-mandibular portion of the dep. 

 md. muscle and ventral to the above-mentioned ligament. In other 

 respects the ramus has the same course and distribution in the two 

 species 



It is in the branchial nerves that we may look for some of the great- 

 est differences between the larval and adult nervous system of any 

 urodele amphibian. On the other hand we find between the IX-X nerve 

 complex of a Neeturus larva of 35 mm. length and of an adult scarcely 

 any appreciable differences. At both periods the resemblances to the 

 larval Spelerpes are as striking as in the other cranial nerves. The 

 ramus communicans according to Miss Bowers contains general cu- 

 taneous fibers only. In fact it has a communis component also. As 

 the ramus approaches the r. jugularis VII it divides, the general cu- 

 taneous part joining the latter ramus and the communis portion pass- 

 ing into the r. alveolaris YII. In Spelerpes the r. communicans, r. 

 pharjmgeus IX and r. posttrematicus IX leave the ganglion as a com- 

 mon trunk; in Neeturus the r. posttrematicus arises separately. In 

 both species the r. pharyngeus sends a r. pretrematicus along the hyoid 

 arch. lii Neeturus the r. supratemporalis X, lateral line, leaves the 

 ganglion along with the motor nerve to the levator muscle of the first 

 branchial arch. In Spelerpes the latter nerve is given off from the 

 r. posttrematicus IX. In both species the r. auricularis X is distinct 

 from the r. supratemporalis X, with no such anastomosing as occurs in 

 Amphiuma and Siren. There are, however, some differences in the 

 composition of the main divisions of the nerve in the two forms, the r. 

 auricularis of Spelerpes having apparently almost identical arrange- 

 ment with that of Amblystoma. The r. posttrematicus IX in both spe- 

 cies sends an anastomosis of general cutaneous and motor fibers to the 

 second branchial nerve. Tn both Neeturus and Spelerpes the second 

 branchial nerve (vagus 1) is well developed with characteristic pharyn- 

 geal, pre-and posttrematic rami having the usual innervation. Branches 

 of general cutaneous and motor composition supply the levator and 

 depressor muscles of the first and second gills and the overlying skin. 

 In each the branch supplying the depressor and levator muscles of the 

 first gill receives the anastomosis from the first branchial nerve already 

 mentioned. The third branchial nerve (vagus 2) has undergone much 

 reduction. In Neeturus it arises close to and is almost a part of fhe 



