ON THE BRAIN OF ONE OF THE 

 SALAMANDERS {Plethedon glutinosus) 



By Gideon S. Dodds 

 Introduction 



In a former'' paper the author published an account of the cranial 

 nerves of Plethedon glutinosus. In the following pages is given a 

 description of the brain of the same form. 



Before entering into the more minute account of the structure of 

 the brain, a few notes of a general nature may be of interest to those 

 without a knowledge of the technicalities of brain structure. Plethe- 

 don glutinosus is a salamander occurring in the eastern United States. 

 It is chiefly terrestrial in its habits. It measures from 5 to 7 inches 

 in length, the specimens used in this study being about 5 inches long. 

 Such a brain as that of Plethedon glutinosus is an excellent example of 

 a brain showing the various parts in simple relations, being in some 

 respects better than the much studied brain of the frog. The brain of 

 Amhly stoma tigrinum, our common "water dog" in Colorado would 

 be equally satisfactory. 



Fig. 17 gives a good idea of the general external^appearance of the 

 brain. At first glance, it appears to have nothing in common with 

 such a brain as that of man, but the difference is not so great as might 

 be imagined, for, in such a brain as this one, there are present in simple 

 form, the same parts which make up the brain of the higher vertebrates. 

 The real difference between this brain and that of man is in the relative 

 development of the different parts. 



In the brain of higher forms, the enormous relative growth of the 

 cerebral hemispheres has obscured the real structural relations of the 

 different parts. Fig. 17 shows that in this brain, the cerebral hemi- 

 spheres are not "hemispheres" at all, but instead, two somewhat cylin- 

 drical bodies, no more conspicuous than the other parts of the brain. 



' "The Cranial Nerves of one of the Salamanders {Plethedon glutinosus), " The University of Colorado 

 Studies, ni. 87, 1906. 



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