280 



branch is the ramus pharyngeus of Müller's descriptions, the re- 

 maining, main nerve trunk being a ramus branchio-intestinalis. 



The further course of these two vagus nerves was not traced. 

 The first spinal nerve arises, close behind the vagus, by two roots, 

 one dorsal and one ventral. The ventral root, as it runs outward to 

 the membranous side wall of the neural tube, crosses the dorsal sur- 

 face of the vagus root, passing close to it. The two spinal roots issue 

 by separate foramina through the neural tube, and, although they lie 

 close together outside the tube, there is no apparent interchange of 

 fibres. A ganglion then forms on the dorsal root, and from it arise 

 dorsal, anterior, and ventral branches. No ganglion forms on the 

 ventral root, that root immediately separating into dorsal, horizontal, 

 and ventral branches, the ventral and dorsal branches closely accom- 

 panying the corresponding branches of the dorsal root. 



The second spinal nerve arises close behind the first one, the 

 ventral and dorsal roots of the nerve, in one specimen, having their 

 origins, from the spinal cord, six and eight 20 ft sections, respectively, 

 posterior to the corresponding roots of the first nerve. The ventral 

 root of this second nerve, and also the corresponding roots of the 

 more posterior spinal nerves, were frequently double in the specimens 

 examined, one root arising a number of sections posterior to the other. 

 No anterior branches could be satisfactorily traced from any of the 

 spinal nerves posterior to the first nerve. 



The dorsal branches of these anterior spinal nerves all run up- 

 ward along the lateral surface of the neural tube. The horizontal 

 branches of the ventral roots run directly outward into the trunk 

 muscle, and were not, so far as could be determined, accompanied by 

 any fibres from the dorsal root. The ventral branches run downward, 

 dorsal and external to the vagus, along the internal surface of the 

 dorsal trunk muscles, the ventral branch of the first nerve sometimes 

 traversing the deeper layers of these muscles. Having reached the 

 ventral edge of the dorsal trunk muscles, the nerve turns outward 

 around that edge, and, piercing the superficial "schiefer Bauchmuskel" 

 of Müller's descriptions, reaches the inner surface of the skin, where 

 it could not be further satisfactorily traced. The ventral branch of 

 the fourth spinal nerve, in the one specimen examined, pierced the 

 superficial abdominal muscle immediately in front of the most anterior 

 of the lateral mucous glands. This gland lay opposite the 6th muscle 

 segment, close to the 5th septum; the nerve thus here lying approx- 

 imately internal to that septum. The ventral branches of the 3rd, 

 2nd, and 1st, spinal nerves reached the skin, respectively, in exactly 



