76 'Journal of Cojiiparative Neurology and Psychology. 



formation (Figs. 3 and 6). Just cephalad of the level of this figure 

 there is a large transverse band of thick medullated fibers w^hich 

 connects the substantia gelatinosa of one side with that of the other 

 or possibly with the opposite commissural nucleus. There is 

 shown in this figure a broad medullated connection between the 

 commissural nucleus and the homolateral spinal V nucleus and 

 formatio reticularis, and also fascicles of commissural fibers in 

 the commissural nucleus. 



A very short distance caudad of the level of Fig. 6 the commis- 

 sural nucleus greatly expands and merges laterally with the spinal 

 V nucleus and funicular nucleus and ventrally with the formatio 

 reticularis (Fig. 7). This complex area may also contain a por- 

 tion of the visceral sensory commissure and nucleus, though no 

 part of it can be recognized as such. It is not possible to analyze 

 this area into its component parts on the basis of microscopical 

 appearances in Weigert sections, as I have done in Ameiurus. 

 Short tracts of medullated and unmedullated fibers pass through 

 it in all directions, many crossing the median line. A vestige of 

 the nucleus ambiguus extends as far back as the level here figured 

 under the commissural nucleus. The relations shown in this 

 figure continue essentially unchanged far back into the spinal 

 cord, where the area in question gradually shrinks in size and 

 passes over into the dorsal cornua. 



The first spinal nerve is a fusion of two or more nerves. The 

 dorsal roots enter the complex area just mentioned, which at the 

 level shown in Fig. 8 is designated cornu dorsalis. At the level 

 of the origin of the second spinal nerve (which joins the first in the 

 brachial plexus) the relations are similar, though the dorsal cornu 

 complex is much smaller and in its dorsal portion the true dorsal 

 cornu is structurally well defined, with a small but distinct funic- 

 ulus dorsalis laterally of it. At the level of the dorsal root of 

 the third spinal nerve the dorsal area of gray matter is still further 

 reduced, the dorsal cornu and funiculus are still more distinct and 

 the other portions of the dorsal gray complex are reduced to a 

 small median vestige. The ventral ramus of this nerve also effects 

 connection with the brachial plexus for the mnervation of the 

 pectoral fin. The fourth spinal does not enter the brachial plexus. 

 The pelvic fin is innervated chiefly from the ramus ventralis of 

 this nerve and by a smaller twig from the fifth spinal. 



