CEREBRAL NERVES 245 



culate ganglion or palatine branch of the facial and the otic gang- 

 lion of the third division of the trigeminal (Jacobsons anastomosis}, 

 a continuation of this branch extending forwards, close to the 

 palatine branch of the facial. 1 In the higher Vertebrates, the 

 large lingual branch forms a gustatory nerve supplying the tongue, 

 tonsils, and epiglottis : this nerve is apparently already indicated 

 in Dipnoans. 



The vagus has a very wide distribution, and is not limited to 

 the head but extends into the trunk. It includes a sensory lateral 

 line branch, pharyngeal ( = palatine), and branchial branches ; the 

 last-mentioned fork over the second and following gill-clefts and 

 supply the mucous membrane and muscles of the branchial appar- 

 atus in branchiate forms. Its visceral branch supplies the larynx, 

 heart, swim-bladder or lungs, and a considerable portion of the 

 digestive tract (gullet, stomach, and more or less of the intestine). 

 In pulmonate Vertebrates a reduction takes place of the motor 

 components of the branchial nerves along with the corresponding 

 muscles (Fig. 180). 



The origin of both glossopharyngeal and vagus by numerous 

 roots, and the fact that they give off branches in the region of the 

 pharynx and visceral arches in which a metameric arrangement 

 can be recognised, indicates that they correspond originally to a 

 number of separate nerves. 



The lateral branch of the vagus, as already mentioned (p. 242), 

 does not belong originally to this nerve, but to the lateral nervous 

 system of the head, having a similar central origin to that of the 

 acustico-facial group, with which it may even be directly con- 

 nected by a commissure outside the auditory capsule (Protopterus). 

 There is a special ganglion at its origin from the medulla 

 (Fig. 179), and its exit from the skull by the same foramen as the 

 vagus is evidently secondary. After giving off a supratemporal 

 branch, it extends along the trunk to the apex of the tail, and may 

 subdivide into several branches, some of which may be situated 

 directly under the skin and others (like the main lateral nerve of 

 Elasmobranchs and Dipnoans), beneath the lateral muscles close 

 to the vertebral column. All these branches supply the sensory 

 organs belonging to the lateral line system. 2 



The so-called spinal accessory (accessorius Willisii) is a true 

 cerebral nerve, and can already be recognised in Elasmobranchs, 

 in which it is included in the vagus, from the posterior roots 



1 It is possible that the lateral line fibres which may be associated with the 

 glossopharyngeal, and even with the trigeminal, are always derived from the 

 vagus and facial. 



- Certain nerves present in Teleostomes and formerly described under the 

 term " ramns lateralis trigemini," may be included under the. term "ramus 

 lateralis accefssoriiix." They form a sensory system of nerves, provided with 

 ganglia, which are formed typically from somatic sensory fibres derived from the 

 Vth, Vllth, IXth, and Xth cerebral nerves and a varied number of spinal nerves. 

 Branches pass to some of, or even all, the fins, and supply sensory end-buds 

 (q.v.). The so-called lateral nerve of Petromyzon belongs to this system. 



