126 ILLINOIS STATE ACADEMY OF SCIENCE 



ance. These notches appear to be unrelated to any ner- 

 vous structure and may simply represent regions of in- 

 complete chondrification. 



Anteriorly, in a plane midway to the anterior end of 

 the capsule, this planum lateralis bends abruptly ven- 

 trally and forms a vertical plate, extending laterally and 

 ventrally so that the cavum nasi may be said to be 

 roughly divided into two regions, the anterior one related 

 to the cupola and tectum nasale above described, the 

 posterior covered by planum lateralis and antorbitale 

 (Fig. 9). The dorsal margin of this vertical portion of 

 planum lateralis continues medially into a cylindrical- 

 ly shaped process, which as a small beak is inclined 

 anteriorly and is superimposed upon a small enlarge- 

 ment of the posterior margin of tectum nasale (Figs. 

 8, 9). Thus there is formed between the two a small 

 bay, continuous with the large fenestra in the roof 

 of the capsule. No nervous structures were found 

 to be associated with this bay. Just below this beak- 

 like process, the medial part of the ventral margin 

 of planum lateralis is continued by a broad cartilage 

 plate into the posterior lateral angle of the tectum 

 nasale forming the only cartilage support for the 

 nasal organ in this region. It is pierced, however, 

 by a small foramen, the homologue of a similar opening 

 described in the earlier stage (Fig. 9). 



The ventral margin of this vertical plane continues 

 forward into a prominent curved process which lies ven- 

 trally, medially and below the plane of the ventral 

 margin of the septum nasi (Fig. 7, 9). Following 

 Gaupp, who figures a similar structure in the skull of the 

 lizard, this process, closely applied to the anterior sur- 

 face of Jacobsen's organ, as well as the part of it extend- 

 ing into the organ, may be called the vomeronasal cap- 

 sule (Fig. 11). The vomeronasal capsule arises from the 

 planum lateralis by a narrow arm which widens ventrally 

 and turns posteriorly midway between planum lateralis 

 and the septum nasi, and becomes more elongate and 

 more pronounced than in the earlier stage. From the 

 ventral margin of this capsule a prominent process 

 curves posteriorly and ends in the surrounding tissue 



