CEREBRAL NERVES 187 



or intracranial spinal nerves, which have been described as ' ventral roots " 

 of the vagus (see p. 143), have nothing to do with this nerve, and perhaps 

 correspond to a part of the hypoglossal of higher Vertebrates. 



In Fishes and perennibranchiate Amphibians the glosso- 

 pharyngeal leaves the skull through a special foramen, and not along 

 with the vagus, a lateral line branch l of which arises separately 

 from and anteriorly to the rest of nerve, dorsally to the glosso- 

 pharyngeal and near the origin of the sensory part of the facial 

 (Fig. 148). This lateral nerve, which may divide into two or even 

 three branches, extends along the side of the body to the tail, 

 either directly beneath the skin, or close to the vertebral column 

 (e.g. Elasniobranchii, Dipnoi), and supplies integumentary sense 

 organs. 



In Protopterus the vagus also gives off superficial branches which extend 

 along the dorsal, lateral and ventral regions of the body close to the skin. 

 In certain Teleosts (Anacanthini) dorsal and ventral superficial nerves are 

 also present, which have sometimes been described as cutaneous branches of 

 the trigeminal. These require further investigation : they appear to belong 

 mainly to the facial, and from their origin and distribution correspond pre- 

 cisely to the " ramus dorsalis recurrens " of Siluroids. The vagus invariably 

 takes part in their formation, and sometimes also the glossopharyngeal and 

 even the first spinal nerves. 



In tracing the development of the lateral nerves, the nervous elements 

 are seen to be so closely united with the thickened epidermis in the region 

 of the lateral line that it is impossible to say whether the nerve arises in sitii 

 or not ; and this is also the case as regards all nerves (VII. , IX. , X. ) supply- 

 ing integumentary sense organs in the Anamnia. 



In branchiate Vertebrates, the glossopharyngeal gives off a 

 pharyiigeal branch and forks over the first branchial cleft, while the 

 vagus gives rise to branchial branches which are similarly related to 

 the following clefts (Fig. 148) : these branchial nerves supply the 

 muscles and mucous membrane of the branchial apparatus. In 

 Chimsera each of the three branchial nerves arises independently 

 from the brain. It will be remembered that the facial nerve has 

 similar relations to the spiracuiar cleft (p. 185). Both glossopharyn- 

 geal and vagus contain mixed fibres, and become connected in various 

 ways with the trigeminal and facial. In correspondence with the 

 reduction of the gills in higher forms, the branchial branches of the 

 vagus can no longer be recognised, and the glossopharyngeal passes 

 into the tongue as the nerve of taste, giving off also a pharyngeal 

 branch (Fig. 149). This condition is first indicated in Dipnoi and 

 Amphibia. 



The spinal accessory nerve first appears distinctly in Reptiles. 

 It 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 as a collector, 

 taking up fibres from the cervical nerves as it goes. It extends 

 along the side of the medulla oblongata into the cranial cavity, and 



1 The glossopharyngeal also possesses a lateral line branch in many Fishes. 



