CRANIAL NERVES. 



159 



Both vagus and glossopharyngeal are always closely connected with 

 the sympathetic system by anastomoses : in Fishes the glosso- 

 pharyngeal supplies the region of the first (hyobranchial) cleft, while 

 in the higher Vertebrates it passes to the tongue as the nerve of 

 taste, and, like the vagus, gives rise to a pharyngeal plexus. 



Ulat 



FICJ. 130. CRANIAL NERVES AND BHACHIAL PLEXUS OF Scyllium canicula. 



II, optic nerve ; ///, oculomotor ; IV, trochlear ; V a (upper), superficial branch, and 

 V a (lower), deep branch of the first division of the trigeminal (the two branches 

 anastomose at * within the nasal capsule) ; Vbe, maxillo-niandibular branch ; 

 V b , maxillary branch ; V c , mandibular branch ; VI, abducent ; VII, facial ; 

 VII a , its hyomandibular branch ; VIP, its palatine branch ; /A', glossopharyn- 

 geal ; -X", vagus ; Rial, its lateral branch ; ttt, gill-clefts ; 1 to 14, the first 

 fourteen spinal nerves, forming the brachial plexus (Pl.lrach] ; 0, auditory 

 capsule ; Sp, spiracle ; Or, orbit ; AfS, cleft of mouth. 



Spinal Accessory. This nerve arises some distance back 

 along the cervical portion of the spinal cord, in the region from 

 which the fourth to fifth cervical nerves come off; from this 

 point it passes forwards, taking up fibres from the cervical nerves 

 as it goes. It extends along the side of the medulla oblongata 

 into the cranial cavity, there becomes associated with the root of 

 the vagus, and leaves the skull through the same foramen as the 

 latter. It appears plainly for the first time in Chelonia, and 

 supplies certain of the muscles related to the pectoral arch, c.y. 

 the sternocleidomastoid and the trapezius. 



Hypoglossal. This purely motor nerve closely resembles a 

 spinal nerve, and is distributed (having here and there anastomoses 

 with the cervical plexus) to certain muscles lying on the floor of the 

 mouth, and to others extending between the pectoral arch (sternum) 

 and hyoid (which morphologically are trunk-muscles and not vis- 

 ceral muscles), as well as to the muscles of the tongue proper, 

 which are differentiated from the latter. (Compare p. 119). In 

 the Ichthyopsida it is not included within the skull, and is there 



