MUSTELUS L.EVIS. 183 



runs laterally and backward^ and is accompanied by tlie 

 other two of the three orbital branches of the palatinas just 

 above referred to, these latter two branches soon uniting to 

 form a single nerve. Branches, which form anastomoses 

 among themselves, are then given off by the two nerves, so 

 formed, certain of them accompanying the pseudobranchial 

 artery to the spiracular pseudobranch, while others turn 

 downward and forward to the roof of the pharynx. 



These first three branches of the ramus palatinus thus, to- 

 gether, probably represent the nervus prespiracularis of Tie- 

 sing's descriptions of the adult Mustelus. In Wright's (70) de- 

 scriptions of embryos smaller than my own they are probably 

 what he refers to in the words, " Behind the orbit a few 

 twigs, which run backward to the filaments of the mandibular 

 pseudobranch." Wright further says that the main truncus 

 facialis, which is said to arise from the facial ganglion 

 se23arately and independently of these twigs, " forks between 

 the two diverticula of the hyomandibular cleft into the prae- 

 and post-trematic branches." The few twigs that run back- 

 ward to the pseudobranch do not, accordingly, form, in his 

 interpretation of the nerves, the prespiracular division of the 

 facial nerve, this conclusion being based, I believe, on an error 

 of observation, his prsetrematic nerve quite probably being, as 

 is shown below, either a branch of the oticus facialis, or a 

 ligament mistaken for a nerve. 



After giving off these first three branches, the ramus 

 palatinus reaches the lateral edge of the cartilaginous floor of 

 the orbit, and there turns forward, lateral to, and close to 

 that edge, giving off at the same time three branches. One 

 of these three branches runs forward, parallel to, and close 

 to, but slightly ventral to, the main nerve itself, the other 

 two branches running backward and downward. The 

 anteriorly directed branch lies near the dorsal corner of the 

 lateral surface of the pharynx, and gives branches to the 

 tissues there. The main nerve lies slightly dorso-mesial to 

 this branch, and sends branches to the tissues of the roof of 

 the pharynx. Both nerves can be traced forward to the 



VOL. 45, PAUT 2. NEW SEKIES. O 



