292 ILLINOIS ACADEMY OF SCIENCE 



1919. Acanthocephala from the Illinois River, with descriptions 



of species and a synopsis of the family Neoechinorhynch- 

 idae. Bull. 111. Nat. Hist. Survey 13: 225-257. 



1920. Acanthocephala of the Canadian Arctic Expedition, 1913-1918. 



Rep. Can. Arct. Exp. 9, part E. 



THE MORPHOLOGY OF THE ANTORBITAL PRO- 

 CESS IN THE URODELES * 



Geo. M. Higgins, Univeksity of Illinois 



In the development of the cliondrocrania of almost all 

 Urodeles a small process arises from the lower margin 

 of the trabecula, jnst in front of the eye. In the early- 

 stages of Amblystoma pimctatum, where the details of 

 development have been followed more closely, this struc- 

 ture first appears in a larva about 25 mm. long, in 

 which a small cartilage bar develops laterally from the 

 trabecula, considerably back of the choana. This struc- 

 ture has usually been designated the antorbital process, 

 a term most appropriate from the standpoint of its posi- 

 tion, and one used throughout this discussion. 



Before the antorbital process has appeared, a nasal 

 capsule has begun to develop; first, by the indepedent 

 chondrification of an ethmoidal column, which develops 

 from in front backward, and comes to lie along the 

 median dorsal surface of the nasal sac. Later this col- 

 umn unites to the cornu trabeculae in front and the 

 crista trabeculae behind; and, at about the time that the 

 antorbital process begins to develop from the trabecula, 

 a cartilage bar chondrifies laterally from the posterior 

 end of the columna ethmoidalis, partially covering the 

 nasal sac at the choana. By a further growth, this bar 

 expands laterally, anteriorly and posteriorly into a broad 

 plate of cartilage, which, covering the nasal organ, forms 

 the roof of the capsule. Earlier writers on the chondro- 

 cranium of the Ichthyopsida (Winslow, 1898; Terry 

 1906) speak of this plate as the lamina cribosa, a rather 

 inappropriate term, for it is evident that this structure 



* Contributions from the Zoological Laboratory of the University of 

 Illinois, No. 163. 



