NERVES OF THE DOGFISH 373 



posteriorly nearly to the posterior border of the fifth branchial 

 arch. Then it divides into three main branches whose subdivi- 

 sions are distributed chiefly to the wall of the digestive tract. 



THE OCCIPITAL NERVES 



The occipital nerves in Squalus acanthias are variable in num- 

 ber. Two seems to be the more constant number, but in some 

 instances two well-developed and one or more rudimentary ones 

 may be found. In the same head there may occur a difference 

 in number between the two sides. Fiirbringer ('97) reports two 

 or three occipital nerves in Acanthias vulgaris. Following the 

 method of Furbringer, the writers designate the occipital nerves 

 from posterior to anterior by the letters z, y, x, etc. 



The anterior rootlets of the occipital nerve y may be discerned 

 somewhat anterior to the transverse level of the posterior motor 

 roots of the vagus (fig. 51, y). They arise, in marked contrast 

 to the visceral motor roots of the vagus, from the ventral motor 

 column. About six rootlets contribute to the formation of the 

 nerve. After .its formation the nerve passes at once into the 

 vagal canal, sometimes by a distinct foramen. Within the canal 

 (fig. 42, y) it passes back with the vagal complex and divides into 

 a larger ventral and a smaller dorsal portion. The smaller divi- 

 sion, in passing out dorsally through a small canal in the roof of 

 the ear capsule (figs. 49 and 51), is accompanied by a correspond- 

 ing branch of the occipital nerve z, the two being distributed to 

 dorsal trunk muscles. The main portion of the nerve y continues 

 through the vagal canal accompanied by the main part of nerve 

 z. As the two nerves pass into the first interbasal (subspinalis) 

 muscle, or more correctly stated, between its dorsal and ventral 

 portions, they are joined by a ventral branch of the first spinal 

 nerve. This latter nerve contains somatic sensory as well as 

 somatic motor fibers. The three nerves pass back through the 

 muscle and at its lateral border merge into a single trunk, in 

 which, however, the individuality of the contributing nerves is 

 not lost. 



