3 i2 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



is the deep 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 branches 

 which are attached to the skin and ampullae belong to the maxillary nerve, while 

 those which accompany the lateral line canals belong to the buccal nerve. 



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 and ampullae 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 ob served that all of the branches of the fifth nerve are somatic sensory nerves 

 coming from the skin and ampullae of Lorenzini, 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 



