THE CRANIAL NERVES OF ONE OF THE 

 SALAMANDERS {Plethedon glutinosus) 



By Gideon S. Dodds 



Among Urodelan brains, probably those of Neciurus and Proteus 

 have been most studied. Work has also been done upon Diemyctylus 

 viridescens,^ Desmognathus fusca, Ambly stoma tigrinum, Amphiuma, 

 and others. The family Plethedontidae, comprising thirty-five species,' 

 has been little studied. So far as I can learn, the only work done in 

 this family is a study of the cranial nerves of Spelerpes hilineatus by 

 Mary A. Bowers.' 



The brain of Plethedon glutinosus presents no very striking dif- 

 ferences from those of other Urodelans. The general appearance of 

 the dorsal aspect of the brain, and the place of origin of the cranial 

 nerves is shown in figure i. This brain measures 7 to 9 mm. in length 

 and 2 to 2.5 mm. in width at the widest part. Owing to its small size, 

 it is necessary to use microscopic methods in its study. The present 

 investigations were made from serial sections through decalcified 

 heads. In the following account is given a brief description of the 

 cranial nerves of Plethedon glutinosus, including their apparent place 

 of origin and relations of the principal branches. These features are 

 shown in figure 2. 



I. The mode of origin of the olfactory nerve varies in Urodela, 

 sometimes arising by one root, and sometimes by two. In Plethedon 

 glutinosus it arises by two roots. The main root arises from the cephalo- 

 lateral angle of the olfactory lobes toward their ventral aspect. The 

 second, very much smaller root, arises some httle distance back, from 

 the lateral surface of the brain. After a short course forwards, the 

 nerve divides into two branches, which innervate the roof and floor 



' The writer is indebted to Prof. Burt G. Wilder, through whose kindness he secured a valuable paper 

 bearing on the subject. 



2 D. S. Jordan. Manual of the Vertebrates, etc. Eighth edition. iSgp. 



2 Noted by Coghill. Jr. Comp. Neur., 12: 285. 1902. 



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