IX 



CRANIAL NERVES 



335 



The trigeminal nerve issues from the brain at the side of the medulla 

 oblongata near its anterior limit (Fig. 138, B). 



Facial (Fig. 140, VII). — The Seventh nerve also arises from the side 

 of the medulla oblongata, close behind the Fifth (Fig. 138, B). The main 

 stem of the nerve (Hyomandibular, Fig. 140, VII^w) passes out towards 

 the spiracle, over which it forks very much in the same way as the main 

 stem of the trigeminal does over the edge of the mouth, except that here 

 the anterior branch is greatly reduced. This trunk is mainly motor, 

 supplying various muscles connected with the -lower jaw and hyoid arch. 

 It is of evolutionary interest from the fact that in man the muscles 



\d.o 



\S:0. 



VHsa y yn K X X& 



lot. Xk 



vnA/Ti 



Fig. 140. 



Diagram illustrating the arrangement of certain of the cranial nerves in the Dogfish. £, eye ; 

 lat, lateral line nerve ; M, mouth ; v.c, visceral cleft. V, Trigeminal ; Vd.o, deep ophthalmic branch ; 

 Vmn, mandibular branch ; Vmx, maxillary branch ; Vs-o, superficial ophthalmic branch ; VII, Facial ; 

 VII6, buccal branch ; Vllhm, hyomandibular branch ; VIIs.o, superficial ophthalmic branch ; 

 IX, Glosso-pbaryngeal ; X, Vagus ; Xb, first branchial branch ; Xv, visceral branch. 



supplied by this nerve have become spread over the face so that it 

 controls the complicated musculatiire of facial expression. 



The slender Palatine branch (not shown in Fig. 140) passes diagonally 

 outwards and forwards across the floor of the orbit : it is purely sensory 

 and is distributed to the roof of the mouth. 



The two remaining branches are associated with remarkable sense 

 organs of the skin belonging to the lateral Kne system (see below, p. 345). 



The Buccal branch (Fig. 140, VII6) is distributed along with the 

 maxillary division of the trigeminal, from which it is indistinguishable 

 through a great part of its length, and is the nerve of the organs of the 

 lateral line system on the lower surface of the snout and below the eye. 



