CRANIAL NERVES. 



275 



branches, the auricular 

 and the main stem. 

 The auricular is a 

 sensory nerve to the 

 skin. The main stein 

 is a mixed nerve which 

 contains the elements 

 of the spinal accessory 

 or llth nerve of higher 

 types (branch to the m. 

 cucullaris}. Its motor 

 fibres supply the three 

 posterior slips of the 

 petrohyoid muscle, the 

 laryngeal muscles a.nd 

 one of the shoulder- 

 girdle muscles (inter- 

 scapularis). There are 

 no occipital andspino- 

 occipital nerves (ven- 

 tral vagus roots) in 

 Amphibia. 



In the Anura (Fig. 

 153) there are only ten 

 pairs of spinal nerves 

 and the spinal cord is 

 shorter than the ver- 

 tebral column, ending 

 in the filurn terminate 

 (Fig. 153). In the 

 Urodela the spinal 

 nerves are more nume- 

 rous and the' spinal 

 cord extends along 

 the caudal region. In 

 adult Urodeles * and 

 aglossal Anura the first 

 spinal nerve is without 

 a dorsal root ; in the 

 phaneroglossal Anura 

 it is absent in the 

 adult and the first 

 spinal nerve, which 

 leaves the spinal canal 

 between the first and 

 second vertebrae, is 

 really the second. 

 Thid esppnnH rirml 

 nerve joins the bra- 

 chial plexus but it 



* This nerve is present with both roots in the embryo, but the dorsal 

 root disappears in development. It resembles in this respect the occipito- 

 spinal nerves of fishes. 



FIG. 153. Nervous system of the frog (after Ecker). Br, 

 brachial nerve ; Js, ischial nerve ; 0, eye ; Ol, olfactory 

 nerves ; Op, optic nerve ; Spn 1, first spinal nerve ; Sg. 1-10, 



