970 MKS. O. A, MERRITT HAWKES ON THE [Dec. 1 1 



commmiis and conimnnis root of the trigeminus involves the lack 

 of a r. palatinus for this segment. Functionally this is replaced 

 by the forward extension of the r. palatinus VII." This statement 

 is supported by Johnston, who says (15. p. 208) there is " no 

 communis component in the Trigeminus and no viscero-sensory 

 center in this segment." These statements are pi-obably generally 

 ti'ue, biit there are some appai-ent exceptions to it, for in 

 Amphibia, in Aonia, in Gadus, in Amiurus, in fjhimcera, and 

 here in Chlamydoselachus, there are trigeminal visceral branches. 

 It will, however, probably be proved in all these species, as it has 

 been in Amia, that this communis component belongs to the 

 Facialis, and has only secondarily become imited with the Tri- 

 geminus. If the Trigeminus were a bi'anchiomeric nerve we would 

 expect to find a representative of the ramus visceralis, and as such 

 we might have interpreted the visceralis elements which occur in 

 the above-named species ; but if, as Johnston says, the segment 

 to which the Trigeminus belongs has no viscero-sensory centre 

 and little or perhaps no entodermal area., this nerve cannot be 

 branchiomeric at all, for a typical branchiomei-ic nerve should 

 contain (15. p. 262) "a communis component distributed by way 

 of the post-trematic, pre-trematic, and pharyngeal rami to the 

 mucosse " of its entodermal area. 



(&) The mandibular branch, which is almost twice the size of the 

 maxillary, passes obliquely backwards, giving off ventrally a, 

 number (3 or 4) of branches which supply the posterior half of 

 the upper jaw, and must therefore be regarded as representing 

 a portion of the maxillaris. On the caudad side, it sends off 

 numerous small nerves into the masseter muscle. As the r. man- 

 dibularis passes along the lowei- jaw it sends more branches into 

 the masseter muscle, which extends towards the mid-ventral line. 

 At a point just before the insertion of this muscle a nerve is 

 given off which soon divides into two equal branches : one of these 

 supplies the perichondrium of the mandibular cartilage, whilst 

 the other branch divides into numerous small branches which 

 terminate in the skin near the symphysis. The mandibular ramus 

 does not supply the large median muscles which lie in the angle 

 made by the two sides of the lower jaw. The components in the 

 mandibular I'amus ai'e motor and sensory (general cutaneovis), the 

 latter predominating. 



It is somewhat exceptional for the maxillary and mandibular 

 rami to come off directly from the Gasserian ganglion. Does the 

 arrangement indicate (1) a primitive condition, or (2) a specialised 

 condition due to the backward rotation of the angle of the jaw ? 

 Regarding the Tiigeminus as a branchiomeric nerve, it must be 

 borne in mind that the ^yq- and post-trematic rami come imme- 

 diately from the ganglion, a condition still to be found in the 

 Facialis and in many branchial nerves ; later, the pre- and post- 

 trematic branches tend to join for a short distance. The result 

 of this union in the supposedly branchiomeiic trigeminal nerve 

 was to produce the usual maxillo-mandibular trunk. But in 



