CHAPTER IX 

 SPINAL CORD AND BULBOSPINAL JUNCTION 



THE SPINAL CORD AND ITS NERVES 



THOUGH the spinal cord is not included in this survey, some 

 features of its upper segments must be considered here because 

 of their connections with the brain and particularly with the compli- 

 cated structure at the bulbo-spinal junction. The spinal cords of 

 urodeles have not been adequately described, and our material is 

 not suitable for this purpose. Early stages of development of Amblys- 

 toma have been described by Coghill, and the cord of larval Sala- 

 mandra by van Gehuchten ('97). A wide variety of experimental 

 studies of development involving the spinal cord have been reported 

 by others. 



THE SENSORY ZONE 



The slender dorsal gray column is continuous with the nuclei at 

 the bulbar junction, to be described shortly. These cells are activated 

 by the dorsal spinal root fibers and the spinal V and spinal vestibular 

 roots. A few of them in and near the mid-plane are a spinal continua- 

 tion of the commissural nucleus of Cajal and are probably visceral 

 sensory in function. This supposition is supported by Sosa's descrip- 

 tion ('45) of similar cells in the septum dorsale of mammals and birds, 

 which he regards as spinal representatives of Cajal's nucleus. 



Most of the dorsal root fibers immediately upon entrance bifurcate 

 into descending and ascending branches, and the latter in the upper 

 segments comprise most of the massive dorsal funiculi, with which 

 some other fibers are mingled, notably those of the descending 

 vestibular root and bulbar correlation tracts a and h of Kingsbury. 

 The large spinal V root lies ventrally of these funiculi, and below this 

 is a dorsolateral funiculus, containing fibers of the spinal lemniscus, 

 spino-cerebellar tract, and other fibers of spinal and bulbar correla- 

 tion. Many of these dorsolateral fibers decussate, descending from 

 the dorsal gray as internal arcuates. 



THE INTERMEDIATE ZONE 



The intermediate zone is not clearly defined, its gray substance 

 being continuous with that of the motor zone. In the alba the 



125 



