OF THE HEAD IN TUE BATRACHIA URODELA. 119 



combines with it to form the temporal longitudinal muscle 

 supplied in the adult by the first spinal nerve. The glosso- 

 pharyngeal nerve belongs to the first metaotic segment and has 

 no ventral root. To the second segment belongs the vagus root, 

 with which seems to be combined the ganglia of the next two 

 nerves. No ventral root was found in the second segment ; but 

 a ventral root occurs in the last metaotic segment in early stages 

 of development. The first spinal issues from between the skull 

 and first neural arch as a ventral root only ; it joins the second 

 spinal to form the hypoglossal nerve supplying muscles derived 

 from ventral outgrowths of the second, third, and fourth myotomes. 

 The basilar plate of the skull is formed by a backward growth of 

 the trabeculae meeting a forward growth of the base of the 

 occipital arches. It fuses with the auditory capsules, and with 

 the prseoccipital arches developed in the septum between the first 

 and second myotomes. The occipital arches arise in the septum 

 between the second and third myotomes. There is no evidence of 

 the disappearance of segments behind the vagus, and no valid 

 objection to the view that the hind limit of the skull may shift 

 backwards or forwards in the course of phylogeny. At the same 

 time there is no reason to suppose that the ancestors of the 

 Amphibia had more than three occipital segments, when the 

 occipital condyle became clearly defined. 



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