/.( )OLOGY FOR MEDICAL STUDENTS CHAP. 



LOMOTOS (1'iu. 138, III). The Third nerve supplies the four 

 remaining rye-muscles Superior, Inferior and Internal Rectus and the 

 Interior Oblique. It arises from the mesencephalon towards its ventral 



TKI..I MINAI. (Fig. 140, V). The Fifth nerve is the largest of the 

 cranial nerves in the Dogfish. It is given the name Trigeminal inverte- 

 brates from the characteristic fact that it divides into three main branches, 

 kmnsn as the Ophthalmic (I), Maxillary (II), and Mandibular (III) 

 divisions of the nerve. 



Of these branches the ophthalmic passes forwards through the cavity 

 of the orbit and is distributed eventually to sensory cells in the skin on 

 the dorsal side of the snout. In Acanthias it divides into two, a ventral 



s.r 



FIG. 139. 



oph.s 



(.IfrtW/Aifls). View of rkht orbit with the eyeball and its muscles. A, eyeball in 



position; !', eveb.ili removed. c.r, Kxtcrnal rertus ; i.o, inferior oblique ; i.r, internal roctus ; 



mf.r, inferior r--riii,; >>pli.s, superficial opthalmic nerves ; s.o, superior oblique; s.r, superior rectus ; 



.', supporting table for eyeball; II, optic nerve; III, oculomotor (branch to inferior oblique); 



. tii^'emiiial (p, deep ophthalmic branch ; 2, mundibular branch ; 3, maxillary 



. \ \lb, facial (buccal branch). 



deep ophthalmic branch (Fig. 140, Vd.o) which passes forwards beneath 



the su;>rrior reel us muscle and a superficial ophthalmic (Fig. 140, Vs.o) 



lying more dorsully, along the mesial wall of the orbit, and enclosed 



mirwn sheath with the similarly named branch of VII. In 



an tin -re is no separate deep ophthalmic branch. 



maxillary (Fig. 140, Vinx) and the. mandibular (Vmn) divisions 



:uinal, which in Scylliinn are fused together into a common 



trunk for some distance, pass respectively to the upper and to the lower 



the mouth. The maxillary, purely sensory, is distributed to the 



skin of the root of the mouth and the ventral side of the snout, while 



nulibular carries the motor fibres for the muscles connected with 



the lower jaw together with sensory fibres for the same region. 



