738 • B. W. KUNKEL 



medially and laterally and the cartilages of the two sides are 

 nearly parallel. The dorsal margin of the cartilago paraseptalis 

 lies slightly above the level of the ventral margin of the septum; 

 further anteriorly, where it is more nearly horizontal, its medio- 

 dorsal margin is at the level of the lower margin of the septum. 

 The postero-dorsal angle of the paraseptal cartilage comes to lie 

 in contact with the planum antorbitale for a very short space so 

 that the fenestra basalis is almost completely surrounded by car- 

 tilage. It fails, however, to fuse with the planum antorbitale, as 

 in Lacerta until a much later stage {c.p., fig. 10). 



The cartilago ectochoanalis is a posterior prolongation of the 

 solum nasi which forms a short process ventral and lateral to the 

 choana, with its dorsal surface concave and ventral surface con- 

 vex, forming thus a trough-like projection. It is differentiated 

 from the cartilago paraseptalis only by a shallow incision at its 

 posterior end. 



The fenestra basalis through which the choana passes poste- 

 riorly is vertical and transverse in position and is situated below 

 the level of the ventral margin of the septum interorbitale. In 

 the stage modelled the fenestra is not completely separated by 

 cartilage from the fissura orbitonasahs because of the failure of 

 the cartilago paraseptalis and planum antorbitale to fuse dorsally. 

 The ventro-lateral margin of the fenestra projects posteriorly as 

 the short cartilago ectochoanalis, above which the lateral margin 

 of the fenestra is incised to form the broad sinus nasalis posterior. 

 The medio-ventral margin is likewise incised to form the sinus 

 paraseptalis. The fenestra is oval with the long axis oblique 

 from dorso-medial to ventro-lateral, and with its dorsal end more 

 acute than the ventral. In the Emys embryo modelled the dorsal 

 end of the fenestra is not closed by cartilage but by a mass of 

 dense connective tissue between the planum antorbitale and car- 

 tilago paraseptalis. 



The two fenestrae narinae together form a large round foramen 

 which, as it were, truncates the nasal capsule anteriorly. Unlike 

 that of Lacerta, which faces ventrally and laterally, that of Emys 

 is directed anteriorly in a vertical transverse plane. Dorsally 



