Terry — The N<isal Skeleton of Amhlystoma punctatum. 105 



result of the growth of the ethmoidal plate in these regions the 

 nasal capsules are connected by a broad commissure which has 

 the form of an arch covering dorsally and laterally the hinder 

 part of the internasal space. The Fenestra ethmoidalis has 

 been obliterated through chondrification, but the cartilage 

 here is thin as compared with the dorsal and lateral parts of 

 the plate. This manner of growth of the ethmoidal plate 

 explains, then, the adult form of the nasal septum and its 

 relation to the internasal space. Intermaxillary glands were 

 not present in this or preceding stages, the space being filled 

 with mesenchyma. 



The medial nasal process (Pr. n. med.) has begun to take 

 part in forming a roof over the anterior part of the nasal sac, 

 its dorsal edge bending laterally and presenting several irregu- 

 lar projections. The ventral margin inclines laterally also 

 toward the ventral surface of the main nasal sac ; it is sepa- 

 rated from the conical end of the trabecula and horn by the 

 medial incisure (Inc. med.) the width of which is greater than 

 in Stage III. The medial incisure leads from the internasal 

 space into the narrow cave (Sub. s.) between the under 

 surface of the nasal sac and the upper concave side of the 

 Cornu trabeculae. Into the lateral part of this space the 

 medial portion of the organ of Jacobson (J. O.) has grown, 

 and through the space from the latter organ to the olfactory 

 foramen stretches the large branched Jacobson'a gland 

 already mentioned. The end of the trabecular horn supports 

 Jacobson's organ, around the side of which it is bent. 



The antorbital process at this stage is turned forward 

 toward the internal naris ; its free end presents two little 

 tubercles, one pointing forward, the other laterally. The 

 caudal end of the nasal sac overhangs the antorbital process 

 and the curve of the latter appears to be in adaptation to the 

 adjacent posterior naris. 



The Lamina cribrosa (L.) covers the caudal half of the main 

 sac. It is connected with the side wall of the cranium oppo- 

 site the whole length of the olfactory foramen and a little 

 way caudad of this. As it, stretches outward it becomes nar- 

 rower, terminating opposite the groove which separates 



