1906.] NERVES OF CHLAMYDOSELACHUS ANGUINEUS. 971 



C'hlmnydoselachus an intermediate condition is found, for the 

 niandibnlar ramus has bound up with it a portion of the ramus 

 maxillaris. If the upper and lower jaws in this species were of 

 normal length it miglit be thovight that maxillary and mandibular 

 I'ami wei-e taking the first step towards union, but on account of 

 the great length of the jaws, which have undoubtedly considerably 

 pulled back the mandibular as well as pushed back the hyoman- 

 dibular and following nerves, it seems more probable that this 

 Imckward extension of the jaw has either incompletely torn apart 

 the maxillary and mandibular rami or prevented their complete 

 union. If, however, the Trigeminus is to be regarded as of 

 cerebro-spinal rather than of bi-anchiomeric type, it might be 

 considered as primitive indeed, consisting of a dorsal sensory 

 ramus (r. maxillaris) and a ventral mixed ramus (r. mandibu- 

 laris); but again, when we consider the influence of the specialised 

 jaw, we have as much ground for supposing that the jaw has 

 produced a splitting of a common sensoro-motor trunk as that 

 the condition now found is a remnant of a. primitive state in 

 which each cei-ebro-spinal '• nerve " was repi-esented by two 

 ilistinct rami. 



(c) The profandjus nerve, or ramus, originates, as stated above, 

 from a small enlargement on the inner side of the Gasserian 

 ganglion ; hence, as in Chimoira (3) aird Petromyzon (16), there 

 is undoubted evidence that, at the present time, the profundus is 

 a branch of the Trigeminus, although in origin it belongs to a 

 more anterior segment (15. p. 206). On entering the orbit the 

 nerve passes between the large rectus externus muscle and the 

 ci'anial wall, sending dorsally a long ciliarj^ nerve which ends 

 4xround the upper part of the eyeball. The main nerve then 

 passes outward, pai'allel with the oculo- motor nerve, to which it 

 sends or from which it receives an anastomosing branch. Five mm. 

 beyond the oi'igin of the ciliary branch the pi'ofundus passes 

 somewhat ventrally between the eyeball and the external rectus 

 muscle to disappear in the eyeball, near the point of insertion of 

 the venti-al part of the external rectus muscle. The profundus 

 passes for about 1 cm. under the covering membrane of the eye- 

 ball, emerging near the point where the optic nerve oi'iginates 

 from the eyeball. The nerve then passes anteriorly and out of 

 the orbit immediately to the outer side of the attachment of the 

 inferior oblique muscle. Almost at once the nerve divides into a 

 number of branches, which spread over the olfactoi'y capsules 

 immediately below the skin. No motor fibres were found in this 

 i-egion. No fusion with the superficial ophthalmic facialis (as in 

 Ohimcera and other cartilaginous fishes) has been found, nor with 

 the superficial ophthalmicus trigeminus (fis in Amia). In Petro- 

 inyzon (16) Johnston states that one complete branch of the 

 pi"ofundus is derived from the Yllth ganglion, and "would cor- 

 i-espond with the typical ramus ophthalmicus superficialis YII." 

 of Selachians. He also found a second branch, of which the 

 fibres are supposed to be derived from the trigeminal ganglion ; 



