NERVOUS SYSTEM. 59 



IV. Trochlearis (or Patheticus). 



V. Trigeminal (or Trifacial). 



VI. Abducens. 



VII. Facial. 



VIII. Auditory. 



IX. Glossopharyngeal. 



X. Vagus (or Pneumogastric). 



XI. Spinal Accessory (or Accessory of Willis). 



XII. Hypoglossal. 



As has been described, the spinal nerves contain both sen- 

 sory and motor roots. The cranial nerves present some dif- 

 ferences from this. Thus nerves I., II., and VIII. are purely 



Fig. 61. Diagram of cranial nerves (shark), a, alveolaris; b, buccalis; c, 

 cerebrum; cb, cerebellum; cl, chorda tympani ; e, ear; er, external rectus muscle; 

 f, inferior rectus muscle; g, Gasserian ganglion; h, hyoid cartilage; hm, hyoman- 

 dibular cartilage ; hnui, hyomandibular nerve ; ;', internal rectus muscle ; io, inferior 

 ■oblique muscle ; j, Jacobson's commissure ; /, lateralis branch of vagus ; ni, mouth ; 

 //;r, Meckel's cartilage; vid^ mandibularis ; vix, maxillaris superior ; ;/, nose; 0, 

 optic lobes (mesencephalon); op, ophthalmicus profundus; w, ophthalmicus super- 

 ficialis; /, pinealis; pi, palatine; po, post-trematic branch; pn, intestinal (pneu- 

 mogastric) branch of vagus ; /;-, pre-trematic branch ; ptq, pterygoquadrate cartilage ; 

 s, spiracle ; so, superior oblique muscle ; sr, superior rectus muscle ; /, thalamen- 

 cephalon ; I-X, cranial nerves; 1-5, gill clefts. 



sensory ; III., IV., and VI. are solely motor ; while the others 

 are mixed, i.e., contain both motor and sensory fibres. 



Both the olfactory and the optic nerves are usually regarded 

 as differing from all other cranial nerves in that they arise as 



