DEVELOPMENT OF THE SKULL OF EMYS 735 



In a younger embryo than that modelled (fig. 30) the solum nasi 

 is separated from the septum completely behind a slender lamina 

 transversahs anterior so that the entire posterior half of the solum 

 nasi is free from the septum much as in Lacerta, as Gaupp has 

 shown. Accordingly the foramen praepalatinum of Emys cor- 

 responds to the anterior portion of the cleft separating the sep- 

 tum from the cartilago paraseptahs, and the portion of the solum 

 nasi which is continuous with the septum behind the foramen 

 praepalatinum represents a portion of the cartilago paraseptalis 

 which has become extended medially and fused with the septum. 

 The solum nasi exhibits in the region lateral to the cartilago para- 

 septalis in the younger embryos several foramina which in the 

 embryo modelled have become occluded but which are still mani- 

 fest as thinner spots in the floor of the capsule. 



The cartilago paraseptahs of Emys is relatively much shorter 

 than that of Lacerta and does not unite in the stage modelled 

 with the planum antorbitale by its posterior end. At a later 

 stage there is such a fusion similar to that in Lacerta. But, 

 unlike the condition in Lacerta, the choanae of Emys he well pos- 

 terior to the cartilago paraseptalis instead of anterior to the pos- 

 terior end of the cartilage. 



The relationship of parts of the floor of the capsule of Emys 

 may be derived from that of Lacerta by a widening in a median 

 direction of the cartilago ectochoanalis so that the fenestra 

 basahs is moved posteriorly by an obhteration from in front, and 

 at the same time by a broadening of the cartilago paraseptalis 

 in its posterior half so that it fuses with the septum. That these 

 changes may actually have taken place is indicated by the nasal 

 capsule of the younger embryos in which, as has already been 

 noted, the cartilago paraseptahs is separated from the septum for 

 its entire length, and by the fact that, lateral to the cartilago 

 paraseptalis, the floor of the capsule is perforated by a series of 

 fenestrae arranged in a longitudinal row. 



Anteriorly, the solum nasi projects forward as a short process 

 ventral to the apertura nasahs externa; it passes over smoothly 

 into the paries nasi on the two sides. While the floor of the cap- 

 sule is nearly horizontal, except for a ventral crest along the lower 



