1906.] XERVES OP CIILAMYDOSELACHUS ANGUIXEUS. 969 



t'ome into close contact, they are loosely oi- tightly bound together 

 by connective tissue, but, in all cases except the one mentioned 

 above, in such a way that a sepai'ation can be eiiected by careful 

 dissection. The smaller branches and these pseudo-unions vary 

 considerably on the two sides of the same specimen and in 

 different specimens. The variability, which is met with in every 

 system of Chlamycloselachus, suggests that the species has con- 

 siderable anatomical instability. 



I. The Trigeminal Nerve. 



The Ti'igeminal nerve oiiginates by one bi-oad root from the 

 side of the medulla., at a lower level than the first and second 

 roots of the Facialis, but on a level with the auditory and hyo- 

 mandibular roots. This root is almost completely hidden in a 

 side view by the buccalis ganglion. Shortly after the root leaves 

 the brain it swells into the Gasserian ganglion, which is rounded 

 <.m the inner, but flattened on the outer side, where it is covered 

 by the buccalis ganglion (Plate LXYIII. figs. 2 & 3). The pre- 

 sence of one root only is surprising when it is known that Iwth 

 sensory and motor components are present. It is probable that 

 serial sections would demonstrate two roots. On the inner side, 

 somewhat anteriorly, there is a small swelling fi-om which the 

 profundus and the superficial ophthalmic V. are given off side by 

 side as nerves of equal size, to pass forward parallel to one another 

 for a short distance (Plate LXYIII. figs. 2 & 3). 



The maxillary and mandibular rami are immediately given ofl' 

 from the end of the ganglion, there being no common maxillo- 

 mandibular trunk. 



(«) The inaxillaris, the smaller of the two branches, passes 

 obliquely downwards across the orbit, sending many branches 

 ventrally. These, together with the branches into which the 

 main nerve itself divides, suppl}^ somewhat more than the anterior 

 half of the upper jaw with the associated tissues. The smaller 

 maxillary branches divide into a gi-eat number of small branches 

 at the outer part of the masseter muscle, over which the majoiity 

 pass, to terminate just above the mucosa of the roof of the mouth 

 and along the under and outer side of the upper jaw cartilage. 

 Although this nerve does not usually contain communis fibres, 

 the distribution of some of the above branches suggests that such 

 may be present. No visceral branches have been found which 

 might correspond with those of the maxillaris V. and mandi- 

 bularis V. which Cole describes in Chimcet-a (3. p. 650). But 

 the many small branches which terminate in the mucosa of the 

 roof of the movith probably consist of communis fibres, and 

 therefore represent the visceralis branch of the maxillai-is V. of 

 Chimcera. Herrick, who in his Menidia paper regards the Tri- 

 geminus as a branchiomeric nerve, says (13. p. 414) : — " The 

 pretrematic ramus, or r. maxillaris, has typically only general 

 cutaneous fibres;" .... "the absence of a prefacial fasciculus 



64* 



