340 ROBERT J. TERRY 



thick piece, triangular in section, extending cephalad toward the 

 crista semicircularis (fig. 27). Its medial surface bounds the 

 common meatus; a dorso-lateral surface enters into the floor of 

 the recessis lateralis superior; the ventro-lateral face is turned 

 toward the recessus lateralis inferior. Ethmoturbinal I reaches 

 the olfactory fenestra in the thick layer of mesenchyma filling 

 this space (fig. 1); ventrally it is separated by a wide stretch 

 from the level of the solum nasi; anteriorly it enters into the 

 caudal boundary of the hiatus semilunaris. Ethmoturbinal II 

 (figs. 1, 13, 26) is represented by a small cartilaginous plate, 

 with precartilaginous margins, jutting mesad from the lateral 

 nasal wall between ethmoturbinal I and the posterior cupola. 

 From the level of the olfactory fenestra its long axis extends 

 ventro-rostrad. It terminates a considerable distance above 

 the plane of the fenestra basalis. 



The cavity of the posterior cupola lies behind ethmoturbinal 

 I, occupying the caudal extremity of the nasal capsule. The 

 walls formed by the septum nasi, lamina infracribrosa, lamina 

 transversalis posterior and antorbital plane, are smooth. The 

 cavity opens anteriorly and ventrally into the common meatus 

 of the nose and the fenestra basalis. 



Ethmoidal region in smaller embryos 



The first evidences of chondrification in the ethmoidal region 

 were found in embryos of 12 nun. in which the process was mani- 

 fested in the septum nasi (fig. 17). In van Wijhe preparations 

 the ventral part of the septum was stained blue (fig. 6), appear- 

 ing in the form of two streaks extending from the trabecular 

 plate forward, side by side and separated by a less deeply stained 

 tract. In embryos of 15 mm. chondrification of the septum has 

 extended dorsally, reaching its greatest height in front. It is 

 now a single median cartilage (fig. 18). The septum is contin- 

 uous with the trabecular plate caudally, and in front gives off a 

 pair of arching processes from its dorsal margin (fig. 7). The 

 latter, which may be called the parieto-tectal cartilages, are at 

 this stage in relation to the roof and lateral wall of the anterior 

 one-third of the nasal cavity. Whether these processes are pri- 



