Terry — The Nasal Skeleton of Amblystoma pwictatum. 101 



hook a little way in front of the dorsal corner of the trabecu- 

 lar crest. 



The anterior trabecular plate (Ant. tr. pi.) underlies the 

 cephalic end of the brain and connects the trabeculae some 

 distance caudad of their extremities ; its cephalic margin is a 

 little behind the level of the junction of the trabecula and the 

 base of the rod (Col. eth.). I could not discover that this 

 plate chondrifies independently of the trabeculae. 



Stage III. 

 Amblystoma 21-24mm. Figs. 3 and 8. 



The nasal sac, which has a cephalo-caudal direction in the 

 13 and 17mm. larvae, now holds an obhque position, the 

 caudal end being farther from the middle line than th« 

 cephalic extremity. About one-third of the nasal sac is 

 cephalad of the brain and the internasal space is correspond- 

 ingly increased. The organ of Jacobson (J. O.) is quite 

 prominent, projecting laterally as well as ventrally. The 

 groove dorsad of it is relatively wider than in the younger ani- 

 mals and its floor now shows a slight convexity, best marked 

 in front. 



A narrow cartilaginous cranial floor is formed by the an- 

 terior trabecular plate and by a ledge extending from the medial 

 side of the trabecula. The broad horn of the latter (Co. tr.) 

 sends its upturned end around the under surface of Jacob- 

 son's organ. The blunt end of the trabecula projects a little 

 way beyond the cephalic margin of the Cornu. The an- 

 terior part of the main nasal sac does not rest directly upon 

 the upper concave surface of the Cornu, as does Jacobson's 

 organ, but is separated by a narrow but well defined Sub- 

 nasal Space (Sub. s.) which is occupied by a loose web of 

 mesenchymal tissue and by some of the branches of Jacob- 

 son's gland. 



The antorbital process (Pr. ao.) juts out from the trabecula 

 just caudad of the Olfactory Window (Fen. ol.) ; between it 

 and the Cornu trabeculae there is a wide notch, or bay, in which 



