62 ILLINOIS BIOLOGICAL MONOGRAPHS (62 



the choanal region; it extends laterally a short distance, then turns forward 

 and later uniting to the planum «tectale forms a part of the lateral wall and 

 floor of the capsule. This has almost universally been called the antor- 

 bital process; but the larva of Cryptobranchus shows what it really is. 

 In my second larva of this animal the pterygo-quadrate bar extends for- 

 ward from the hinge of the lower jaw and joins the trabecula at the same 

 point from which the antorbital projects in other Urodeles. In Ranodon 

 judging from Wiedersheim's figure (1877, Fig. 69), there is a similar con- 

 nection of the pterygoquadrate with the anterior part of the skull. Else- 

 where in all described Urodeles, as far as I have been able to discover, 

 there is only an extension of the pterygoid process forward from the quad- 

 rate towards the capsular region; and even in the adult Cryptobranchus 

 (and this holds also for the Japanese species, as figured by Parker) the 

 connection between the pterygoid and the structures farther forward is lost. 



In all the Anura, on the other hand, the pterygoid cartilage is connected 

 throughout life with the nasal capsules. In this respect Ranodon, and to 

 a less degree Cryptobranchus, approach the Anura more closely than any 

 of the other Urodeles. It is usual to regard this arch as the homologue of 

 the upper jaw of the Elasmobranch, which, with the development of the 

 osseous upper jaw of the Teleostomes and higher groups, has lost its original 

 function as a part of the feeding apparatus, and has fused with the side of 

 the cranium, its middle portion dropping out in the process. It may be 

 remarked parenthetically, that the name palato-quadrate commonly 

 given this arch is incorrect, as it contains no palatal element and no part of 

 the palatine bone is developed from it. 



In no Elasmobranch is there any extension of the pterygoid as a distinct 

 process beyond the curve of the arch of the upper jaw. On the other hand, 

 in all of the Amphibia there is such a forwardly directed process, the 

 antorbital, already referred to. It would then apparently follow that the 

 antorbital process of the Urodele, is in its basal part, the anterior end of the 

 pterygoquadrate, while its anterior portion is a new formation. That this 

 interpretation is correct, is supported by all of the Anura that I have 

 studied. 



In my earlier stages of Salamandra (in which there is no connection at 

 any stage between the pterygoid process and the structures farther for- 

 ward) the antorbital process is developed and extends forward beneath the 

 nasal capsule; but as yet it is unconnected distally with any other cartilage. 

 Just dorsal to the base of this process, both the ophthalmic and super- 

 ficialis branches of the fifth nerve pass into the capsular region. Thus 

 the antorbital process is ventral to these nerves. In the oldest larva 

 that I have of this genus, the roof of the capsule (planum tectale) has 

 extended back so that its posterior margin overlies the base of the antor- 

 bital, while between the tectale and the antorbital there is a very large gap. 



