50 ILLINOIS BIOLOGICAL MONOGRAPHS [50 



posterior angle the tectale is continuous with the anterior portion of the 

 pterygoid process, the two uniting to form a large triangular plate, Parker's 

 ethmo-palatine cartilage, which continues forward into his pre-palatine 

 spur; this process covering Jacobson's organ and part of the nasal sac. It 

 is obvious that the terms ethmo-palatine and pre-palatal spur, used by 

 Parker, are misleading for reasons stated before in this paper; and it would 

 seem that the term planum tectale had best be used to designate this entire 

 process. The extension forward of the pterygoid is the normal condition 

 in the Anura, but among the Urodeles it is known to exist only in Crypto- 

 branchus and Ranodon, this ancestral character having been lost in other 

 Amphibia. 



On the lower outer surface of the trabecula, at its junction with the 

 capsular parts, is the foramen for the nasalis nerve, hence this is the orbito- 

 nasalis of the Urodeles. It follows from this identification, that the bar 

 ventral to this is the greatly reduced antorbital while the roof of the foramen 

 is as plainly tectale. The main part of the nerve courses forward through 

 the cartilage, and the anterior end of the foramen lies on the ventral side 

 of the tectale (Fig. 35). Another branch of this nerve emerges on the 

 dorsal surface of the trabecula, turns medially and then ventrally and 

 passes through another foramen to the medial side of the nasal sac parallel 

 with the olfactorius. Just medial to this last foramen is the olfactory 

 foramen for the I nerve which passes downward to reach the olfactory 

 organ. From this it follows that the cartilage region anterior (and mor- 

 phologically dorsal) to these nerves and their foramina must be the columna 

 ethmoidalis. 



At about its middle, the lower margin of the planum tectale gives rise 

 to a short bar, at first extending ventrally and then medially and a little 

 posteriorly, just above the anterior end of the organ of Jacobson. From 

 near its base this bar gives rise to a cylindrical rod, which runs obliquely 

 forward and inward to become continuous with the lower lateral surface of 

 the planum verticale near its anterior end. In this course it passes, first, 

 on the outer surface of the connection of the organ of Jacobson with the 

 olfactory sac, then along the ventral lateral margin of the sac itself. The 

 medial end of the ventral bar is connected with a second cylindrical 

 cartilage, passing obliquely forward and inward to join the dorsal lateral 

 side of the verticale at its tip, medial to the naris. Where the more ventral 

 of these two cylindrical bars unites to the verticale, it expands into an 

 alinasal cartilage, which supports the anterior part of the nasal organ, and 

 is separated at its anterior end from the distal margin of the verticale by 

 a crescentic groove, the external naris (Fig. 74). 



The two cylindrical cartilages just described, have been known in the 

 literature as the dorsal and ventral bars or processes, terms that convey 

 nothing as to their homologies. From a study of Parker's early larva, it is 



