VERTEBRATES. 



301 



This line of organs is plainly seen on the side of the body 

 in most fishes. On the head, however, it frequently 

 branches greatly and becomes enormously extended in 

 this way. The occurrence of these structures in aquatic 

 forms only would suggest that their function is connected 



FIG. 110. Diagram of cranial nerves, a, alveolaris nerve*, b, buccalis nerve; 

 c, cerebrum; cb, cerebellum ; ct, chorda tympani; e, ear; er, external rectus 

 muscle; /, inferior rectus muscle; g, Gasserian ganglion; h, hyoid cartilage; 

 hm, hyomandibular cartilage; hmd, hyomandibular nerve; i, internal rectus 

 muscle; to, inferior oblique muscle; j, Jacobson's commissure; Z, lateralis 

 branch of vagus nerve; m, mouth; me, Meckel's cartilage; md, mandibularis 

 nerve; mx, maxillaris superior nerve; n, nose; o, optic lobes; op, ophthal- 

 micus profundus nerve; os, ophthalmicus superficialis nerve; p, pinealis;p/, 

 palatine nerve; po, posttrematic branch; pn, intestinal (pneumogastric) 

 nerve; pr, pretrematic branch; ptq, pterygoquadrate cartilage; s, spiracle; 

 so, superior oblique muscle; sr, superior recfus muscle; t, 'twixt-brain ; 

 I-X, cranial nerves; 1-5, gill-slits. 



with that element; but what that function is, is not well 

 understood. 



The taste-organs are within the mouth, principally on the 

 tongue. They are poorly developed in some vertebrates, 

 better in others. 



The olfactory organs are always placed in front of the 

 mouth. They consist of a membrane folded so as to ex- 

 pose a great amount of surface, and this surface is covered 

 with the sensory structure, connected with the ends of the 

 olfactory nerve. In the fishes the sacs containing this 



