98 Trans. Acad. Set. of St. Louis. 



later stages as cranial side-walls. Each Crista trabeoulae, 

 highest caudally, gradually descends toward the snout. There 

 is no union between the trabeculae in front ; antorbital pro- 

 cesses are not present and with the exception of the Cornua 

 trabecularum no mention is made by Winslow of a cartilagin- 

 ous nasal skeleton. 



These conditions were found as described, in the larva of 

 12 mm. which I studied. 



Stage I. 



Amblystoma ISmln. Fig. 1. 



The simple, somewhat oval, nasal sac lies laterad of the 

 brain, extending beyond its level ventrally. A groove on its 

 lateral surface separates Jacobson's organ from a dorsal prom- 

 inence. The narial passage is simple; everywhere, except 

 laterally, its walls are thick. A narrow off-shoot from the 

 general cavity close to the internal naris leads into Jacobson's 

 organ. 



The trabeculae (Tr.) are unconnected anteriorly and lie ven- 

 trad of the brain beyond which they project to the level of the 

 cephalic ends of the olfactory organs. The Crista trabeculae 

 (C. tr.) reaches forward, almost to the level of the nasal 

 jsac and olfactory bulb where it ends in an abruptly descend- 

 ing edge. The trabecula is triangular in section from the 

 crest as far as the horn. Opposite the latter it sends a blunt 

 process (Medial Process of the trabecula; Pr. med.) mesad 

 toward its fellow, and also dorsad a little way. The trabecu- 

 lar horn (Co. tr.) lies beneath and supports the olfactory 

 sac ; in this function the neighboring part of the trabecula 

 also shares. 



The left "Processus" antorbitalis is present in the form of 

 a slender stick of cartilage between the olfactory organ and 

 eye-ball. It is just behind the internal naris and is continued 

 as a prechondral rod medialwards to the trabecula, joining it 

 at the level of the cephalic end of the Crista. 



Ossification of the roof of the cranium is already well ad- 

 vanced at this stage but there is no bone in the olfactory region 



