730 B. W. KUNKEL 



REGIO ETHMOIDALIS 



The ethmoidal region of Emys exhibits greater differences from 

 that of Lacerta than does any other region of the chondro- 

 cranium. It has been carefully described by means of models 

 by Seydel ('96), whose results are in the main confirmed by the 

 present study, and by Nick ('12) in Chelydra serpentina, Chelone 

 midas, and Dermochelys coriacea. The homologies of certain 

 parts, however, which were not discussed by Seydel, have been 

 determined by study of a more complete series of embryos. To 

 Seydel's observations there are only a few details to be added. 



In striking contrast to the condition in Lacerta, the capsule 

 is more compact and is made up of continuous plates of cartilage 

 interrupted only to a limited extent by fenestrae and not modified 

 by alar processes and a complicated concha; besides this, the whole 

 capsule has undergone a bending in a ventral direction. The 

 differences in general form of this region in Lacerta and Emys are 

 to be correlated with the greater strength of the jaws of chelonians, 

 which condition requires that the bones against which the lower 

 jaw impinges (premaxillare, maxillare, vomer, palatinum) have 

 a more solid foundation to rest against than in such forms as 

 the snakes and lizards. Gaupp ('06, p. 45) has already called 

 attention to the fact that the form of the olfactory capsule is 

 controlled as well by the structure of the jaws as by the form of 

 the olfactory sac itself. 



The olfactory capsule is divided into two symmetrical halves 

 by the septum nasi which continues in an anterior direction from 

 the septum interorbitale. The postero-dorsal wall of the capsule 

 accordingly forms the anterior boundary of the orbit and the 

 anterior wall forms the anterior limit of the head. On account 

 of its position relatively far ventral to the other portions of the 

 skull, its ventral wall projects below the level of the lower edge 

 of the septum interorbitale to afford a prominent, and at the 

 same time soUd, support for the upper jaw. Besides the septum 

 nasi which forms the median wall of each half, the cartilages 

 making up the walls of the capsule may be differentiated into the 

 tectum nasi dorsally, the paries nasi laterally, the solum nasi and 



