CRANIAL NERVES OF CHIMiERA MONSTROSA. 659 



represented by the internal mandibular or post-branchial (facial) of fishes. Pinkus (67) 

 follows Stannius in not distinguishing a prse-spiracular nerve, but describes it as a 

 branch of the palatine. He refers to two palatines — a superior and an inferior. The 

 latter arises from the base of the superior, and corresponds to the prse-spiracular division 

 of the Vllth, or the chorda tympani of mammals. The latter homology is recognised 

 by Pinkus ; and as he also identifies correctly the mandibularis internus (which is a 

 motor nerve in Protopterus as in Chimsera), he must be considered the first author to 

 (unwittingly) confirm the view held by Balfour. 



The above quotations show, I think, that two nerves have been described under the 

 name of ' mandibularis internus.' In fishes the post-branchial division of the facial has 

 been uniformly described as the internal mandibular (cp. Stannius, Jackson and 

 Clarke, and Pinkus), but in Amphibia the nerve corresponding to the prse-branchial 

 of fishes is wrongly referred to as the internal mandibular (cp. Strong). The facial 

 proper of fishes, therefore, just over the hyomandibular cleft, divides into 3 nerves, 

 which are : (1) palatine or visceral ; (2) prse-branchial or prse-spiracular, arising from 

 the base of (1) ; (3) post-branchial or post-spiracular, or internal mandibular. Both (2) 

 and (3), may, as first pointed out by Stannius, be continued ventrally on to the pharynx. 

 This fact, it seems to me, has been too often overlooked in considering the homology of 

 the chorda tympani. 



My reasons for regarding the chorda tympani as a prse-branchial nerve are as 

 follows : — 



(1) Assuming that there are no visceral clefts between the spiracle and the mouth, 

 and the evidence in favour of these is well known to be far from satisfactory, the 

 branchial divisions of the facial of fishes should be related respectively to the mandibular 

 and hyoid visceral arches. The prse-branchial should course along the posterior edge of 

 the mandible, and may be continued ventrally on to the pharynx in the immediate 

 vicinity of the mandibular arch. The post-branchial, on the other hand, should course 

 along the anterior edge of the hyoid arch and supply its muscles, and may also be 

 continued on to the pharynx between the hyoid and mandibular arches. These facts 

 were first pointed out by Stannius. Further, the prse-branchial should be essentially 

 a splanchnic sensory nerve, and the post-branchial a splanchnic motor nerve. 



(2) In fishes having a spiracle, the prse-spiracular nerve arises from the base of the 

 palatine. 



(3) It is obvious from (l) and ;(2) that the nerve I have described in Chimcera as 

 the chorda tympani is at least a prse-branehial nerve, and corresponds, for example, to 

 the prse-spiracular of Lcemargus. 



(4) The essential features in the distribution -of the chorda in Mammals are : (a) it 

 passes (morphologically) under the tympanum; (b) anastomoses with the lingual 

 (mandibular) division of the Vth (this is perhaps of not so much importance, as it seems 

 to remain physiologically distinct) ; (c) supplies a gland ; (d) enters into branchial 

 relations with the mandible ; (e) supplies the tongue. As I have pointed out, (6) is not 



