436 CROCODILIA 



CHAP. 



At a deeper level the orbit is partly divided from the lateral tem- 

 poral fossa by a strong column which is formed by the meeting of 

 a downward process of the postfrontal with an inner process of the 

 jugal, and an ascending process of the ectopterygoid (cf. Fig. 108, 

 p. 458). This arrangement adds considerably to the strength of 

 the skull. The lateral temporal fossa is bordered in front by 

 the column just described ; below by the jugal and the quadrato- 

 jugal, which is firmly wedged in between the jugal and quadrate ; 

 behind by the quadrate ; above by the postfrontal, which forms a 

 strong superficial bridge with the squamosal. This rests upon 

 and often fuses with the quadrate and an intervening transverse 

 wing-like extension of the lateral occipital bone. By this 

 squamoso-postfrontal bridge part of the original temporal fossa 

 is divided into the lateral one just described, and a dorsal fossa. 

 The latter is bordered by the postfrontal, squamosal, and united 

 parietals. This dorsal temporal fossa is consequently not 

 homologous with that of the Parasuchia, a vestige of which is 

 however present in many, especially in young skulls of Crocodiles, 

 in the shape of a narrow passage which extends backwards from 

 the dorsal fossa, bridged over by the junction of the parietal with 

 the squamosal, and bordered below by the occipitals. 



The size of the upper temporal fossae stands in an inverse 

 ratio to that of the lateral fossae. In the older Eusuchia the 

 upper were the larger of the two. The temporo-mandibular 

 muscle which lifts or shuts the lower jaw arises from the walls 

 of the upper fossa, passes beneath the jugal arch, and is inserted 

 into the supra-angular portion of the lower jaw. In the more 

 recent Crocodiles this muscle is more and more superseded by 

 the pterygo-mandibular muscle, which, arising chiefly from the 

 dorsal surface of the much broadened-out pterygoid bone, fills 

 the widened space beween the latter and tlie quadrate, and is 

 inserted into the outer surface of the os angulare of the lower 

 jaw. This muscle, owing to its general disposition, is capable of 

 mucli more powerful development and leverage than the temporo- 

 maxillary muscle, which latter, being more reduced, allows the 

 dorsal fossae to be more and more closed up by the surrounding 

 bones. 



'I'lie fossae are still comparatively large in the long-snouted 

 genera Gavialis and Tomistoma, which live entirely upon fish and 

 scarcely chew their food, wliilst these holes almost completely 



