23] THE SKULL OF AM lURUS— KINDRED 23 



the neural arches. All except the first have very well developed dorsalis and 

 lateralis rami and usually an additional dorsal sensory ramus which proceeds 

 dorsally to the epidermis (Fig. 12). The ramus lateralis of the first post-vagal 

 nerve (Fig. 17) descends obliquely to the muscles in the ventral wall of the body 

 between the parts of the shoulder girdle, and in this way is comparable to 

 the somatic hypoglossal nerve of the higher groups. The first two m^uscle 

 segments have no visible innervation. The third and fourth muscle segments 

 are innervated by the distinct rami dorsales of the second and third nerves. 

 The rami laterales of these two nerves descend, as did the ramus lateralis 

 of the first nerve, to the musculature between and around the developing shoul- 

 der girdle. 



The work of Gegenbaur (1887), Sagemehl (1884, 1885, 1891), Froriep 

 (1901), Stohr (1882), Dohm (1901), Sewertzoff (1895), Van Wijhe (1882), 

 Fiirbringer (1897), and others on the relation of the trunk and head in the occipi- 

 tal region has been reviewed by Gaupp (1906). He emphasizes the work of 

 Fiirbringer as a step in the right direction for the imderstanding of this ques- 

 tion and I refer briefly to some of the points of interest in the researches of 

 Fiirbringer (1897). 



According to this author, the crania of the Teleosts m.ay be divided into 

 two parts, and anterior paleocranium, ending with the vagus, and a part pos- 

 terior to this, the neocranium. The neocranial condition arose from the assimi- 

 lation of body segments and is represented in the occipital part of the cranium 

 by skeletal segments and nerves. The primitive type of neocranium is 

 termed the protometameric and is represented in the present day forms in 

 the crania of the Selachians and the Amphibia. When more elements are 

 assimilated the auximetameric condition is reached. This type of neocranium 

 is found in the higher fishes and in the Amniotes. The distribution and occur- 

 rence of nerves posterior to the vagus are used by the author in his analysis 

 of the types of neocrania in the different groups. The paleocranial nerves 

 end with the vagus and the neocranial are those, which, before becoming 

 included within the cranium, were of a free spinal type. These nerves so in- 

 cluded are called the 'spino-occipital' nerves and are further divided into two 

 categories; those enclosed in the protometameric neocranium are knowTi as the 

 'occipitale' nerves and those in the auximetameric neocranium as the 'occipito- 

 spinale' nerves. He explains the difference in number and appearance of these 

 nerves in the different animal groups as the result of more or less assimilation 

 of vertebrae and atrophy of somites. In his diagrammatic representations of 

 the condition in the Selachians, the last 'occipitale' nerve is represented by the 

 letter 'z' and the first of the 'occipito-spinale' nerves of the higher fishes and 

 the Amniotes as 'a,' the homologue of the first free spinal nerve of the Sela- 

 chians. Holocephala, Ganoids, Dipnoi, Teleosts, and Amniotes possess an 

 occipital region of the auximetameric type. According to Fiirbringer, different 

 numbers of vertebrae and segments take part in the formation of this region, 



