willard: cranial nerves of anolis carolinensis. 75 



the fine fibers. It forms a bundle about two thirds the diameter of 

 the main trunk of IX, which it joins to form the pharyngo-laryngeal 

 nerve (fig. K, Plate 2, fig. 4, phx-lar.). From this ramus are given off 

 several small twigs to the constrictor muscle of the jugular vein (p. 44). 

 These are fibers somewhat larger than the viscero-sensory fibers, but 

 with extremely delicate myelin sheaths, and for this reason they were 

 not discovered in the series of sections plotted; but in another series 

 through this region (Fig. 7v), especially fixed, the innervation of these 

 muscle fibers was determined. Of the three twigs shown in the draw- 

 ing only one is given off from the superior laryngeus before its union 

 with the ramus pharyngeus IX. 



It is important to note that these visceral muscle fibers (Plate 7, fig. 

 23, co'st. vn. j.i.), although striated, do not draw off any of the coarse 

 fibers from the vagus, but are supplied by nerve fibers which are indis- 

 tinguishable from the other fine fibers when mingled with them, but 

 which nevertheless possess slight differences, as is shown when they 

 are grouped together. We probably have in the innervation of this 

 muscle a case analogous to that of the ciliary muscle, which primarily 

 is non-striated, but in the sauropsida is striated. If the striated muscle 

 fibers surrounding the jugular vein have been differentiated from the 

 smooth muscle cells of the vessel wall, which are believed to be 

 innervated by non-medullated postganglionic neurons, the question 

 'suggests itself as to what modification of the innervation has accom- 

 panied that of the musculature. As before stated the nerve fibers 

 show a slight medullation indicating to that extent a change from the 

 sympathetic type, but their continued course through the ganglion, 

 suggesting direct central origin, was not shown in the sections although 

 this was clearly demonstrated for the more heavily medullated fibers 

 passing into the pharyngo-laryngeal branch. Onuf and Collins ( :00, 

 p. 174) describe two nuclei for eft'erent neurons of nerves IX and 

 X in the mammals (cat). The dorsal glossopharyngeal and vagus 

 nucleus, is, according to them, the nucleus of origin for the efferent 

 sympathetic fibers carried in the roots of these nerves; the ventral, 

 nucleus ambiguus, gives rise to the nerve fibers innervating muscles 

 ■of visceral origin but of somatic function, derivatives of the striated 

 gill-arch musculature of the fishes. The spinal accessory nerve, when 

 present, is exclusively of the latter type. The innervation of the 

 special jugular vein muscle of Anolis suggests a condition intermediate 

 between the sympathetic and the viscero-motor of the cerebro-spinal 

 type. The slight development of this latter component in nerves IX 

 and X made it impossible to establish this suggestion as a fact through 

 the analysis of the central terminations. 



