190 



TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



a sharp U and pressed vertically against the fork of the vomer and the median cavity of the 

 mesethmoid. In the oblique front view (Fig. 76) the opposite maxillae are seen to end 

 dorsally in two sharply diverging, rounded processes. The opposite pairs of maxillary 

 processes surround the vertically placed premaxillary tracker or rostral bone, meeting both 

 above and below it. The rounded dorsal processes fit dorso-posteriorly into thick cartila- 



pa 



soc 



/ot 



deth \ prf 



ep 



/ pf m 



Cyprinus carpio 



Fig. 74. Cyprinus carpio. Side view. 



ginous or bony caps called the " submaxillary cartilages " by Starks and " cartilaginous rods " 

 by Edwards, which are more or less fully ossified. These fit against smoothly rounded, 

 condylar-like "preethmoid" projections from the anterior forks of the vomer. By means 

 of these rolling condylar surfaces of the vomer and preethmoids the maxillaries can rock 

 back and forth as the mouth is protruded and withdrawn. 



The parts described above are protected from lateral dislocation by an anterior or 

 maxillary process of the short palatine, which is lateral to the proximal end of the maxilla; 

 from its front end a ligament passes forward to the outer side of the dorsal process of the 

 maxilla. In the closed position of the mouth the lower border of the mandible is directed 

 partly upward. Depression of the mandible by the longitudinal throat muscles (genio- 

 hyoideus and sternohyoideus) causes the ascending process of the dentary, which is very 

 far forward, to move forward and downward together with the fold of skin that passes to 

 the lower border of the maxilla. Since the ends of the premaxillae are tied by ligaments 

 to the lower end of the maxillae, and since the latter are fastened to the ascending process 

 of the dentary, depression of the mandible also tends to pull the premaxillae downward. 

 The forward movement is checked at the end by the median tracker and paired ligaments. 



