114 Trans. Acad. Sci. of St. Louis. 



is formed in the perirhinal tissue in connection with the rod 

 through chondrification of the medial nasal process and it is 

 separated in all the larval stages studied by a notch (Incisura 

 medialis) from the trabecula. 



Parker ('77) has described under the name of "foremost 

 paraneural cartilage," a term used by Huxley ('74), a shell- 

 like cartilage over the nasal sac of Siredon. The cartilage 

 is concave forward, one limb directed laterad over the nasal 

 sac, the other cephalad along the mesal margin of the sac. 

 It is at first independent but later joins with the trabecular 

 plate. This appears much like the rod (Col. eth.) and the 

 Lamina cribrosa. 



Wilders's ( '92) figure of the ethmoidal region of Salamandra 

 larva shows very much the same conditions which I have 

 described in Stage III. A rod arches over the olfactory 

 nerve and extends cephalad at the side of the internasal space ; 

 a process goes laterad in front of the level of the antorbital 

 process ; a bridge connects the cartilages of opposite sides at 

 the level of the anterior margins of the olfactory foramina, 

 forming the dorsal boundary of an ethmoidal window. The 

 origin of these cartilages is not given in the description. 



Gaupp ('93) in his well known splendid work on the pri- 

 mordial cranium of Rana, has, after Born, given the name 

 Eth7noidalpfeiler, Columna ethmoidals, to a little pillar of 

 cartilage which grows upon each side from the dorsal sur- 

 face of the already formed anterior trabecular plate. These 

 two pillars grow caudad and laterad over the olfactory nerves 

 around which they help to form a cartilaginous ring by uniting 

 with the side walls of the cranium (the trabecular crests). 

 Thus the olfactory foramen is formed. An ethmoidal win- 

 dow, filled with mucous tissue, is made through an inclination 

 of the ethmoidal columns toward each other. In Fig. 12, Taf. 

 XIV, there is a little salient angle on each column directed 

 dorso-medially and helping to bound the window. 



The roof of the hinder division of the nasal skeleton in 

 Rana arises in connection with the anterior part of the cranial 

 side wall as far forward as the level of the ethmoidal plate 

 which has formed at the site of the ethmoidal window as in 



