44 ILUNOIS BIOLOGICAL MONOGRAPHS 144 



forward, and, bending at right angles the bar has joined to the ventral 

 margin of the trabecula in the region where the antorbital process occurs in 

 all Urodeles. In the five weeks larva, there is no extension forward of this 

 bar beyond its connection with the trabecula; but in the older larvae, a 

 small process extends forward toward the capsule, an apparent continua- 

 tion of the pterygoid; so that an antorbital process is formed which resem- 

 bles in detail those of most other Urodeles. Because of the lacK of older 

 stages, I have no evidence as to the connection of the antorbital to the 

 capsule, nor can I say just when the resorptive processes take place which 

 establish the adult condition of the complete separation of the pterygoid 

 from the capsular region. 



Regarding Cryptobranchus as primitive, then it would appear that the 

 Urodelan antorbital process is in reality composed of the anterior end of a 

 pterygoid plus an anterior extension which secondarily becomes associated 

 with the nasal region. In the Anura, both larva and adult, the pterygoid 

 unites with the anterior part of the trabecula, as in the larval Crypto- 

 branchus, suggesting here a common ancestry; and this relationship tends 

 to support the original conclusion of Gaupp that the antorbital process of 

 Urodeles, at least in its basal part, and the "palatine cartilage" of the 

 Anura are homologous structures. The anterior part of the antorbital, 

 however, is something else and may not be a part of the original pterygo- 

 quadrate arch; accordingly it would seem that in those Urodeles in which 

 the pterygoidal condition is lost, that the entire structure had best retain 

 the name antorbital process. 



Winslow (1898) has described, in his second stage of Ichthyophis, an 

 isolated cartilage in front of the anterior end of the pterygoid, which he 

 calls the "palatine cartilage" ; and interprets it as being a part of an original 

 "palato-pterygoid-quadrate" arch. This cartilage can hardly be called a 

 palatine, and the triple term applied to the pterygo- quadrate is a misnomer 

 for the palatine bone is not cartilaginous in origin. It would appear, 

 however, as though this small cartilage is a part of the pterygoid which at 

 one time was connected to the antorbital process, and to the more proximal 

 pterygoid. In his earlier stage, Winslow describes a small antorbital 

 process which arises much as in the Urodeles from the trabecula. In my 

 material, this process has united to the more anterior parts of the capsule 

 outlining the foramen orbito-nasalis; and from its relation to the isolated 

 part of the pterygoid we are safe in assuming that these parts were at one 

 time in continuity, and in that sense the Caecilians are related to the 

 common ancestor, from which Cryptobranchus on the one hand, and the 

 Anura on the other, have arisen. 



In the Siberian genus, Ranodon, Wiedersheim (1877, Fig. 69) has 

 figured the relation of the antorbital process to the pterygoid much as it 

 occurs in Cryptobranchus; which fact suggests that these genera may be 



