6o MORPHOLOGY OF THE ORGAKS OF VERTEBRATES. 



hollow outgrowths of the brain itself.^ The olfactory nerve 

 arises from the olfactory lobe, and is distributed to the sensory 

 epithelium of the nose. Like all other sensory ner\-es it is pro- 

 vided with its own ganglion, which may either be included in 

 the brain, or it may be carried out into close proximity with 

 the olfactor}' organ. It is evident that the two cases are reall}- 

 different, and that we can only speak of true olfactory nerves 



Fig. 62. Diagram of cranial nerves in an amniote; nerves //to/f'and VI 

 much as in the ichlhyopsida, and hence omitted. </, accessorius ; c, ciliary ganglion ; 

 ct, chorda tympani ; f, facialis : fin, branches of facialis to facial muscles ; g, glcjSis- 

 pharyngeal ; h, hypoglossal ; /, ramus intestinalis of vagus ; _;, Jacobson's commissure ; 

 /, ramus lingualis ; »/, maxillaris; ;//(/, mandibularis ; (7, ophthalmic ; f?^, otic ganglion ; 

 /, palatine ; s, submaxillary ganglion ; sp, sphenopalatine ganglion ; /. tympanum. 



distal to the olfactor\- ganglion. The connection between the 

 olfactory ganglion and the brain is made by the olfactory tract. 

 The optic nerves, which arise primitively from the ventral 

 sides of the diencephalon, have their ganglia lying upon the 

 superficial portion of the retina (see eye, below). Thev retain 

 their connection with the thalamencephalon throughout life in 



1 In connection with nerves I. and II. it is to be noted that the posterior cranial and the 

 spinal nerves of selachians are at first hollow outgrowths from the brain (or neural crest). 

 Farther, that the definitive nerve of the adult grows back from the ganglion to join the 

 brain in both. These facts tend to invahdate tlie distinction drawn between nerves I. and 

 II. and the others. 



