312 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



ophthalmic nerve. This passes through the orbit ventral to the preceding and 

 leaves the orbit by the orbitonasal canal. Upon tracing it forward it will be 

 seen to join the superficial ophthalmic and to be distributed in common with it. 

 Both of these branches of the trigeminus are pure somatic sensory nerves, arising 

 from sense organs of the skin. 



The two remaining branches of the trigeminus lie in the floor of the orbit. 

 To see them remove the eyeball or study the side where the eyeball was previously 

 removed. A broad white band, the infraorbital trunk, is seen in the floor of 

 the orbit, passing obliquely laterally. This trunk in the dogfishes is composed of 

 the mixed fibers of the maxillary branch of the trigeminus and the buccal branch 

 of the seventh nerve (see below). In the orbit the larger and more medial portion 

 of the trunk is the maxillary branch, but farther out this becomes inextricably 

 mingled with the buccal nerve. In the skate the infraorbital trunk is divisible 

 into three trunks, of which the outer one is the maxillary branch of the trigeminus, 

 the middle one the mandibular branch of the trigeminus, and the inner one the 

 buccal branch of the seventh nerve. As before, however, it should be remembered 

 that there is an admixture of fibers of the fifth and seventh nerves in these trunks. 

 Trace the maxillary branch of the trigeminus and buccal branch of the seventh 

 out from the orbit, along the ventral surface of the rostrum. The branches pass 

 to the region below and in front of the eye, to the medial side of the nostril (in 

 the skate to the lateral side of the nostril also) and to the angle of the jaws. In 

 the smooth dogfish there is a conspicuous branch along the lower jaw which 

 appears to be a part of the mandibular branch of the trigeminus. The maxillary 

 branch is sensory to the skin of the rostrum, while the buccal nerve supplies the 

 infraorbital lateral line canal and near-by ampullae of Lorenzini. 



The fourth branch of the trigeminus is the mandibular branch. In the dog- 

 fishes it separates from the infraorbital trunk where the latter enters the orbit 

 from the brain and passes along the posterior wall of the orbit. In the smooth 

 dogfish part of it seems to accompany the infraorbital trunk forward and then 

 curves to the lower jaw as described above. The mandibular nerve is seen to 

 branch to various muscles in the floor of the orbit (these are gill-arch muscles) 

 and on following it out of the orbit, will be seen to be distributed to muscles 

 of the lower jaw and to send a sensory branch to the skin of the lower jaw, this 

 branch being situated just behind the teeth. In the skate the position of the 

 mandibular nerve was described above as between the maxillary and the buccal 

 nerves. Follow it forward. It curves around the angle of the jaw and supplies 

 muscles of the lower jaw and the adjacent skin. 



It will be observed that all of the branches of the fifth nerve are somatic sensory nerves 

 coming from various sensory organs of the skin, except the mandibular nerve which also 

 contains some motor branches to muscles. As those muscles are visceral muscles, this part 

 of the fifth nerve belongs to the visceral motor system. The deep ophthalmic nerve appears 



