41 8 DEVELOPMENT OF ELASMOBRANCH FISHES. 



run below the superior rectus and superior oblique muscles of the eye. The 

 nerve formed by the coalescence of the superficial and deep ophthalmic 

 branches courses a short way below the surface, and supplies the mucous 

 canals of the front of the snout. It is a purely sensory nerve. Strong 

 grounds will be adduced in the sequel for regarding the ramus ophthalmicus 

 superficial, though not the ophthalmicus profundus, as in reality a branch 

 of the seventh, and not of the fifth nerve. 



The second division of the fifth nerve is the superior maxillary, which 

 appears to me to arise from both the first and second roots of the fifth, though 

 mainly from the first. It divides once into two main branches. The first of 

 these the buccal nerve of Stannius after passing forwards along the base 

 of the orbit takes its course obliquely across the palatine arch and behind 

 and below the nasal sack, supplying by the way numerous mucous canals, 

 and dividing at last into two branches, one of these passing directly forwards 

 on the ventral surface of the snout, and the second keeping along the front 

 border of the mouth. The second division of the superior maxillary nerve 

 (superior maxillary of Stannius), after giving off a small branch, which passes 

 backwards in company with a branch from the inferior maxillary nerve to 

 the levator maxillae superioris, itself keeps close to the buccal nerve, and 

 eventually divides into numerous fine twigs to the mucous canals of the skin 

 at the posterior region of the upper jaw. It anastomoses with the buccal 

 nerve. The inferior maxillary nerve arises mainly from the second root of 

 the fifth. After sending a small branch to the levator maxillae superioris, it 

 passes outwards along the line separating the musculus adductor mandibulas 

 from the musculus levator labii superioris, and after giving branches to 

 these muscles takes a course forward along the border of the lower jaw. It 

 appears to be a mixed motor and sensory nerve. 



The seventh or facial nerve arises by a root close to, but behind and below 

 the second root of the fifth, and is intimately fused with this. It divides 

 almost at once into .a small anterior branch and large posterior. 



The anterior branch is the palatine nerve. It gives off at first one or two 

 very small twigs, which pursue a course towards the spiracle, and probably 

 represent the spiracular nerves of other Elasmobranchs. Immediately 

 after giving off these branches it divides into two stems, a posterior smaller 

 and an anterior -larger one. The former eventually takes a course which 

 tends towards the. angle of the jaw, and is distributed to the mucous mem- 

 brane of the roof of the mouth, while the larger one bends forwards and 

 supplies the mucous membrane at the edge of the upper jaw. The main 

 stem of the seventh, after giving off a branch to the dorsal section of the 

 musculus constrictor superficialis, passes outwards to the junction of the 

 upper and lower jaws, where it divides into tv/o branches, an anterior superficial 

 branch, which runs immediately below the skin on the surface of the lower 

 jaw, and a second branch, which takes a deep course along the posterior 

 border of the lower jaw, between it and the hyoid, and sends a series of 

 branches backwards to the ventral section of the musculus constrictor super- 

 ficialis. The main stem of the facial is mixed motor and sensory. I have 



