20 



Directly under the origin of the superficial ophthalmic will be 

 found a comparatively slender nerve, which passes between the 

 superior and posterior rectus muscles, and forward along the medial 

 surface of the eyeball; it penetrates the anterior wall of the orbit 

 by a separate foramen, and emerges under the superficial ophthal- 

 mic. It is distributed to the skin of the dorsal and lateral surfaces 

 of the snout. This is the deep ophthalmic (ophthalmicus profundus) 

 of the trigeminal nerve. A slender branch (posterior ciliary nerve) 

 passes from the deep ophthalmic near its origin to the posterior sur- 

 face of the eyeball. Farther forward the same trunk gives off an 

 anterior ciliary nerve to the anterior part of the eyeball. 



A large nerve which crosses the floor of the orbit, beneath the 

 eyeball, consists of the maxillary trunk of the trigeminal and the 

 buccal trunk of the facial nerve. These remain associated, even 

 into the small branches. Near the anterior margin of the orbit the 

 maxillary-buccal trunk divides into three parts; the smallest and 

 outer one passes to the surface lateral and anterior to the eye. The 

 other two dip downward and pass in front of the jaw to the ventral 

 surface of the snout. Reflect the skin of the ventral surface of the 

 snout, and by dissection expose these nerves as they emerge from 

 the orbit. The larger branch runs forward close to the median line 

 of the snout, giving off numerous twigs; the other, which appears 

 to be a pure trigeminal branch, is distributed near the angle of the 

 mouth. The fibres of the maxillary trunk supply the skin, while 

 those of the buccal go to the canal organs and ampullae of Loren- 

 zini. 



The mandibular trunk of the trigeminal nerve arises beneath 

 and behind the maxillary. It passes outward in front of the levator 

 maxillae superioris muscle, sending a few twigs into this muscle, 

 and turns downward over the palato-quadrate cartilage. It di- 

 vides here, one part entering the adductor mandibularis muscle, the 

 other passing downward along the edge of the mandible, innervating 

 the skin of the lower jaw and the first ventral superficial constrictor 

 muscle. 



The mandibular and maxillary-buccal trunks of Eugaleus are united until 

 they approach the edge of the orbit, and the palatine branch is much larger; 

 otherwise the trigemino-facial branches are much as in Squalus. 



The hyomandibular trunk of the facial nerve can be found just 

 beneath the skin behind and close to the spiracle. From here it 

 can be followed back to the brain. It arises from the ventral part 

 of the trigemino-facial root, emerging from the cranium through 

 the hyomandibular canal. It divides into a number of branches 

 just beyond the spiracle: 



1. The external mandibular branch consists of two portions, a 

 small anterior nerve extending antero-ventrally to the canals above 

 and below the angle of the mouth, and a larger nerve which passes 

 laterally and suddenly breaks up into a brush of twigs which in- 

 nervate the hyoidean group of ampullae. 



2. The internal mandibular branch arises at about the same 

 level as the external mandibular, but under it, passes inward around 

 the edge of the hyoid cartilage, under the adductor mandibularis 

 muscle, and then forward along the mandibular cartilage. 



3. The hyoid branch separates from the hyomandibular trunk 

 at about the same level as the preceding nerves, and then passes, 

 deep in the tissues, around the angle of the jaw to the ventral side 

 where it is distributed to the superficial constrictor muscles. Sev- 

 eral nerves pass from the hyomandibular trunk and the hyoid branch 

 to the dorsal superficial constrictors. 



