118 Trans. Acad. Sci. of St. Louis. 



of my 40-45mm. Amblystoma. Winslow's Fig. 12 shows 

 that in an Amblystoma of 69mm. the roof of the anterior 

 part of the nasal capsule is very slight but that it is con- 

 tinued into the medial wall without interruption. This 

 roof and medial wall I found to be formed in connection 

 with the Columna ethmoidalis, beginning as the medial nasal 

 process. As iuRana it is in relation to the main-sac only. In 

 Kana this medial wall turns under the upper blind-sac to form 

 the Crista intermedia, a partition between the cavities for the 

 upper and lower blind-sacs. There is no such partition in the 

 stages of Amblystoma which I studied but the ventral edge 

 of the medial wall is free and turns laterally a little way under 

 the main-sac (Fig. 4). The ventral edge of the anterior 

 cupola forms a little shelf beneath the main-sac, while the 

 medial incisure exists. 



In Amblystoma the caudal part of the medial surface of 



the main-sac faces an obliquely placed olfactory window; 



in Raua a corresponding part looks toward a transversely 



placed olfactory foramen ; the middle part is opposite the 



ethmoidal plate (beginning septum); in Eana the same 



is opposite the nasal septum ; the anterior part of this surface 



is covered by a proper medial wall, as it is in the frog. 



Thus the main-sac of Amblystoma agrees with the upper 



blind-sac of Eana in its relations to the medial wall of the 



nasal capsule. A proper medial wall for the inferior room 



of the nasal capsule does not exist in Rana and the same is 



true in larval Amblystoma for that space which contains the 



the medial portion of Jacobson's organ and glands. This 



subnasal space (Sub. s.) is limited medially only by the 



nasal septum ; in the larvae it opens into the internasal room 



throucfh the Incisura medialis while back of the ethmoidal 



plate it is limited by the membrane of the olfactory window 



against which the glands are pressed. The Incisura medialis 



transmits the septal branch of the ophthalmic V and is later 



converted into the apical foramen.* 



♦ There is an analogy between this foramen and the Fenestra naso-basale 

 of Rana in its use as the passage way of a branch of a nasal nerve; but 

 while the adult relations are somewhat similar their development appears 

 to be difEerent. 



