MEDULLA OBLONGATA OF AMBLYSTOMA 381 



GENERAL SUMMARY AND DISCUSSION 



A summarj^ of the more important central relations of the sen- 

 sory roots of the cranial nerves of Amblystoma will be found on 

 page 366 and a summary of their chief secondary connections on 

 page 376 and on page 380 is a summary of the motor tracts and • 

 centers. In the following paragraphs some of the more general 

 results of this study are presented and discussed. 



The external form and histological structure of the medulla 

 oblongata of half grown larvae of Amblystoma resemble closely 

 those of the adults of the lower urodeles, such as Necturus. An 

 accurate analysis of the functional components of the cranial 

 nerves of older larvae and adults of Amblystoma has been pub- 

 lished by Coghill ('02), who is now publishing also a series of 

 correlated physiological and anatomical studies on much younger 

 larvae. The observations here presented may serve to connect 

 these researches by illustrating the functional pattern of the 

 medulla oblongata at an intermediate stage of development. 

 The author also hopes to use them as a point of departure for 

 further studies on the development and functional connections 

 of the cerebellum, midbrain and thalamus of urodeles. 



The factors operating in either the ontogenetic or the phj^lo- 

 genetic differentiation of the correlation centers of the brain cannot 

 be profitably investigated without a precise knowledge of the 

 peripheral relations of each functional system represented in 

 these centers and of the interrelations of these systems at every 

 step in the progress of the nervous impulses transmitted by them 

 during the course of normal functional activity. 



In the present analysis of the central courses of the cranial 

 nerve roots it has been found that the individual fibers of each 

 sensory root of the V, VII, VIII, IX and X nerves bifurcate 

 immediately upon entering the medulla oblongata into ascending 

 and descending branches. The ascending and descending fibers 

 of each root are united into distinct fascicles which retain their 

 individuality from the superficial origin of the root upward and' 

 downward respectively throughout nearly the entire length of 

 the oblongata. All of the somatic sensory root fibers divide in 

 this way and many, if not most, of the visceral sensory fibers also- 



