NERVES OF THE DOGFISH 3(55 



of the roots. Figure 43 shows that the arrangement of the root- 

 lets is in an almost uninterrupted series from anterior to posterior. 

 But in the sheet of fibers at the lateral border of the medulla, 

 formed by these rootlets, the individual branchial nerves soon 

 begin to differentiate, and in cross-section the segmental char- 

 acter of this sheet-like root of the vagus becomes very evident 

 (fig. 42). The four branchial and the single intestinal rami be- 

 come differentiated successively anteriorly posteriorly, the last 

 branchial and the intestinal, in the roots as well as peripheral 

 to the ganglion, being closely related. Without doubt there is 

 individual variation in the arrangement of the rootlets. In a 

 study of cross-sections it is often difficult to distinguish be- 

 tween the individual rootlets, but comparisons between cross- 

 sections and parasagittal sections shows that the variations in 

 the roots of the vagus are very few indeed. 



The visceral vagal ganglionic mass shows a segmentation into 

 four branchial and one intestinal divisions, all more or less in 

 contact, and the last two closely fused. Horizontal and para- 

 sagittal sections show very clearly this segmental arrangement 

 (figs. 41 and 44). The common ganglion of the fifth bran hial 

 and the intestinal nerve is larger than the others and plainly 

 double. Proximal to this last ganglion and related to it there 

 are two distinct roots. One the branchial root, connects with 

 the ganglion more anteriorly and ventrally than does the intes- 

 tinal root. Distally there emerge from the ganglion two nerves, 

 a ventral branchial and farther posteriorly a dorsal intestinal. 

 The motor fibers that pass through this fourth ganglion mass 

 belong to the intestinal division and are of two kinds: coarse 

 ones to the trapezius muscle, and finer, less medullated ones to 

 the wall of the digestive tract. 



Fig. 45 A horizontal section through the roots of the right vagus nerve, 

 showing the four vagal branchial roots and the segmented condition of the lat- 

 eral-line ganglion. X30. 



Fig. 46 A section of the left truncus hyomandibularis VII, cut horizontally 

 through the head, but obliquely to the nerve, showing the components of the 

 truncus and a sympathetic ganglion on the posterior border of the nerve. X30. 



Fig. 47 A section of the left truncus hyomandibularis VII, cut transversely 

 through the head, but obliquely to the nerve, showing the components of the 

 nerve and a sympathetic ganglion on the posterior border of the nerve. Corre- 

 sponds approximately to section 1188 in figure 48. X30. 



