304 C. JUDSON HERRICK 



« 



to be bipolar, with the peripheral process directed outward into 

 relation with both the skin and the myotomes. The myotomes, 

 however, have an independent motor innervation and these mus- 

 cular branches from the giant cells are unquestionably concerned 

 with the muscle sense in relation with the swimming reflex. The 

 physiological as well as the anatomical significance of these rela- 

 tions have been very completely investigated by Coghill. It is 

 known, furthermore, that these giant cells of the spinal cord are 

 derived from the neural crest, some of whose cells are enclosed 

 within the spinal cord, while others migrate outward to form the 

 spinal ganglia. 



I have some observations which suggest that in Amblystoma 

 the cells of the mesencephalic V nucleus are likewise derived from 

 the neural crest, but my series of stages of these very young 

 embryos is not sufficiently complete to enable me to verify this 

 supposition and the question requires further study. 



Upon the hypothesis that the mesencephalic V root serves the 

 proprioceptive function of sensori-motor reflexes from the muscles 

 of the head, the functional advantage of the arrangement de- 

 scribed is obvious ; for we have here provision for the most direct 

 possible connection between the sensory fibers derived from the 

 muscles of the head and the motor nuclei from which these muscles 

 are innervated. 



The visceral sensory roots of the VII, IX and X nerves. These 

 roots are made up exclusively of very fine fibers. The neurones 

 of the ganglion geniculi of the facialis are of small or medium size 

 and so far as observed are unipolar, though but few of these 

 neurones are clearly impregnated in our preparations. All of 

 the root fibers of this system at once enter the fasciculus solitarius 

 (fasciculus communis of Osborn), which is composed almost 

 exclusively of these root fibers. 



The fasciculus solitarius is anatomically the most distinct of 

 all the tracts of the oblongata. Its fibers are fine and many of 

 them (perhaps all) bifurcate in the usual way into ascending and 

 descending branches immediately upon entering the oblongata 

 from the peripher^^ It lies dorsally and medially of the VIII 

 roots and ventraliy and medially of Kingsbury's tract b. The 



