THE NERVOUS SYSTEM 



375 



VII. Facialis. Mixed visceral afferent and efferent. Special somatic afferent. 



VIII. Acoustic. Special somatic afferent. 



IX. Glossopharyngeal. General and special visceral mixed. Somatic sensory (?). 



X. Vagus. General and special visceral mixed. Special somatic afferent. 



XI. Accessory. Somatic efferent (?), and general and special visceral efferent. 



XII. Hypoglossal. Somatic efferent. 



From the evolutionary standpoint it is a significant fact that man 

 has the same ten cranial nerves as are found in fishes and amphibians. To 



HYPOPHYSIS 



ANTERIOR 



PERFORATED 



SUBSTANCE 



SEMILUNAR 

 GANGLION 



OPTIC CHIASMA 



TUBER CINEREUM 



MAMMILLARY BODIES 



LATERAL GENICULATE 

 BODY 



MASTICATOR NERVE 

 ■V 



CEREBELLUM 



Fig. 332. 



SPINAL CORD 



-Human brain stem, showing nerve conne.xions. 

 after Allen Thomson.) 



(Redrawn from Morris, 



these, two nerves are added in amniotes as a result of the addition of 

 vertebrae to the occipital region of the skull, making twelve cranial 

 nerves altogether in amniotes. Between fish and man in the course 

 of phylogenesis few changes in individual cranial nerves have occurred. 

 In all forms above cyclostomes the trochlearis has a dorsal chiasma which 

 is lacking in cyclostomes. The factors in its formation are unknown. 

 The ophthalmicus profundus, which is an independent nerve in cyclo- 

 stomes, becomes united with the trigeminal in remaining vertebrates 

 beginning with the elasmobranchs. With the disappearance of lateral- 



