DEVELOPMENT OF THE SKULL OF EMYS 733 



denly ventrally to form the front wall of the capsule dorsal to the 

 fenestra narina. Posteriorly it passes into the planum antorbi- 

 tale and is continuous with the septum nasi and commissura 

 spheno-ethmoidalis. Between the septum nasi and the anterior 

 extremities of the commissurae spheno-ethmoidales accordingly, 

 the tectum bounds the fenestra olfactoria in front. Laterally 

 the tectum nasi bends smoothly ventrally to form the paries 

 nasi. Anteriorly it slopes abruptly ventrally and almost verti- 

 cally to enclose the pars olfactoria in front. On account of the 

 rounded form of this part, the tectum nasi exhibits in this region 

 two gentle convexities separated from each other by a groove 

 marking the position of the front margin of the septum nasi 

 with which it is in perfect continuity. Below each of these 

 cupulas, immediately above the fenestra narina, there is a short 

 blunt, anteriorly directed process which, in later stages, becomes 

 more conspicuous. To this process may be given the name 

 processus supranarinus {-pr.s., fig. 25). 



The paries nasi forms a practically continuous plate of cartilage 

 of slightly convex form limiting the olfactory capsule laterally. 

 It is continuous medially and dorsally with the" tectum nasi -as 

 well as with the planum antorbitale; ventrally throughout its 

 entire length it is continuous with the solum nasi. Its anterior 

 end passes into the tectum nasi dorsally and ends freely ventrally 

 as the lateral margin of the fenestra narina. This free margin 

 is incised to form a very broad shallow sinus (sinus externus) for 

 the accommodation of the duct of the glandula nasi externa which 

 empties into the entrance passage of the olfactory sac (figs. 14 and 

 27). Posteriorly the paries nasi continues with the solum nasi 

 to form the cartilago ectochoanalis (c.e., fig. 9) which bounds the 

 fenestra basalis ventro-laterally. Above the cartilago ectocho- 

 analis the posterior margin is deeply incised to form a rounded 

 sinus in which the recessus ducti nasopharyngei lies and which 

 I would call the sinus nasalis posterior. The paries may be differ- 

 entiated into a dorsally situated pars olfactoria and a ventrally 

 situated pars respiratoria corresponding to the respective parts 

 of the olfactory sac lying within. These two regions are sepa- 

 rated from each other by a broad, shallow groove, which extends 



