DEVELOPMENT OF THE SKULL OF EMYS 755 



nor posteriorly as the latter. Its antero-lateral margin lies in 

 close proximity to the ventral margin of the dentale. 



The goniale {g.) is a thin, elongated plate of bone situated along 

 the median aspect of Meckel's cartilage, from the posterior end 

 of the latter for one-third of its length. It exhibits a convex 

 median and a concave lateral aspect to fit more closely about the 

 posterior end of Meckel's cartilage medially. Its postero-dorsal 

 angle lies along the median aspect of the fovea articularis. 



Of especial interest in connection with the goniale is the rela- 

 tion of the chorda tympani. In the embryo modelled the nerve 

 enters the goniale at its posterior extremity by means of the cana- 

 lis gonialis which extends forward for a short distance and opens 

 anteriorly on the lateral aspect of the goniale as a well marked 

 sulcus so that the chorda tympani reaches the canahs primordialis 

 and extends further forward in this canal between the goniale 

 on the median side and Meckel's cartilage on the lateral side. 

 In an older embryo (carapace length, 13.5 mm.) a canalis goni- 

 alis is wanting. Instead of this the chorda tympani is lodged 

 in a groove on the median side of the goniale. The nerve passes 

 obliquely forward and ventrally and for a short space lies along 

 the ventral margin of the goniale. The latter then becomes 

 suddenly wider by a ventraUy projecting extension which is 

 lateral to the nerve. For a considerable distance the chorda 

 tympani is thus separated from Meckel's cartilage by the goniale. 

 A foramen finally allows the nerve to pass into the sulcus pri- 

 mordialis. 



A third relationship of the chorda tyiApani and goniale was 

 encountered in an embryo having a carapace length of 16 mm. 

 In this individual the nerve entered the canahs gonialis from the 

 lateral aspect of the bone and both before and after entering the 

 canalis goniahs it lay in a deep groove communicating with the 

 sulcus primordiaHs. 



The complementare is not yet laid down in the embryo mod- 

 elled. In an embryo having a carapace 13.5 mm. long, however, 

 it is present as a triangular plate of bone lying dorsal to the goniale 

 with its anterior end somewhat further forward than that of the 

 goniale. It Ues medially to the ramus mandibularis n. trigemini. 



