104 



MR. E. S. GOODRICH OX THE OCCIPITAL REGIOX 



(3rd nietaotic) has a myotome, a ventral root, but no ganglion. 

 The next and succeeding trunk-segments are complete. That 

 this description is incorrect has already been suggested by Miss 

 Piatt, who has given us a detailed and admiiable account of the 

 development of the head in JS^ectitrus (8). 



Miss Piatt analyses the postauditory region as follows : — The 

 1st somite belongs to the glossopharyngeal segment, develops no 

 myotome and has no ventral root. The 2nd, 3rd, and 4th are 

 vagus segments ; the 2nd somite disappears venti'ally, but its 

 dorsal portion develops muscle which combines with the more 

 fully formed myotome of the 3rd somite. The 4th and succeeding 

 somites develop myotomes. The 3rd, 4th, and 5th grow down 

 ventrally to give rise to the hypoglossal muscles, supplied by the 

 ventral roots of the 4th and 5th segments. The 6th segment 

 (3rd of the trunk) is the first to have a complete spinal nerve, 

 with ganglion, ventral and dorsal root. The first neural aich lies 

 between the 4th and 5th somites. Between the 4th and 3rd 

 somites appears the occipital arch marking the hind limit of the 

 skull ; while between the 3rd and 2nd somites is formed a rudi- 

 mentary preeoccipital arch, which is taken into the auditory 

 capsule. If this account is correct, thei-e are three metaotic 

 segments in the head of Amphibia,, the myotomes of the last two 

 being represented in the adult by the anterior region of the dorsal 

 temporal muscle. 



mx. sop. 



hi/a. br.' ^^^^ 



Dissection of a full-grown Axolotl, showing the skeleton and nerves of the head 

 and three trunk-segments. The cartilage is dotted. "View from left side. 



Coming now to my own observations on Amblystoma, we may 

 begin with a glance at the structure of the full-grown animal as 

 shown in text-figs. 29 and 30 *. The hyomandibular branch of the 

 facial nerve issvies from behind the otic process of the quadrate 



* For explanation of the lettering of these text-figures see p. 120. 



