MUSTELUS L-EVIS. 169 



dibular arch. The second and third divisions of the tri- 

 geminal, in fact, fulfil all the requirements of such a nerve, 

 the second being distributed to the outer face of the pter^^- 

 goid appendage of the mandibular arch, just as the palatine 

 nerves arc distributed to its inner face, and the mandibular, 

 or third division of the fifth, running along the outer face of 

 Meckel's cartilage, in correspondence Avith the distribution of 

 the long descending branches of the palatine in the Ray on 

 its inner face. If this be the posterior nerve of the trabeculo- 

 mandibular visceral cleft, where is its anterior nerve ? On 

 this point it may be well to speak cautiously, but certain facts 

 are highly suggestive. The palato-nasal branch of the fifth 

 in the Ray virtually runs along the ventral outer, a morpho- 

 logically posterior edge of the trabecula — which, as I think, 

 cannot be doubted is the homologue of a visceral arch ; on 

 the other hand, the orbito-nasal nerve (first or ophthalmic 

 division of the fifth) runs along the dorsal, a morphologically 

 anterior edge of the trabecula. 



" It seems to me highly probable, therefore, that the 

 palato-nasal nerve of the fifth (or nerve of Cotunnius) is the 

 anterior division of the nerve of the trabeculo-mandibular 

 cleft, which should run along the morphologically posterior 

 face of the trabecula, and that the orbito-nasal nerve is the 

 nerve of the anterior face of the trabecula, which found an 

 actual aperture only in the marsipobranchii (and pharyngo- 

 branchii ?), where it limits the naso-palatine canal laterally." 



It is impossible to recognise in Mustelus exactly what 

 fibres are included in this palato-nasal nerve of the Ray, and 

 it seems to me that Huxley himself did not have a correct 

 or definite idea of exactly how the nerve is composed. That 

 the nerve contains the terminal portion of the buccalis, as 

 that nerve was described by Stanuius, and as it has since 

 been described by other authors, is evident, and the lateral 

 sensory component of the nerve is certainly not coalesced with 

 the anterior palatine division of the seventh in osseous fishes, 

 as Huxley supposed. That this terminal part of the buccalis 

 belongs to a premandibular arch is, however, extremely pro- 



