EXISTING ORGANISMS— ANATOMY 75 



between the lower jaw and the skull. The changes in the lower 

 jaw involve in the lower classes the addition of an outer series 

 of bones including the anterior dentale, which usually bears teeth, 

 followed by a splcnial and angulare, above which lies the surangu- 

 lare. The coronoid runs back from the dentale above the surangu- 

 lare. The posterior end of the cartilage itself may develop into 

 an articular bone by which the jaw is articulated with the quadrate. 

 All of these parts are present in the existing reptiles. 



The modification of these bones in the mammals leaves the 

 upper jaw with the same parts, excepting the quadrate bone. 



Fig. 50. — Pectoral fin and girdle of dogfi.sh. s, scapula; ss, .suprascapula; c, 

 coracoid; p, propterygium; ms, mesopterygium; mt, metapterygium; rad, 

 radials. (From Wilder's History of the Human Body, with the permission 

 of Mrs. H. H. Wilder and Henry Holt and Company.) 



The lower jaw consists of two mandibles, firmly united in man to 

 form a single bone, consisting of the dentales and possibly the 

 splenial and coronoid bones. Other homologies are obscure, but 

 the angulare is said by Kingsley to be apparently the tympanic 

 bone of the skull. The articulation of the lower jaws with the 

 skull is thus shifted in the mammal to the mandible (dentale?) 

 and squamosal. The articulare and quadrate, freed from this 

 function, are found in the middle ear, the former being certainly 

 the malleus, while the quadrate is possibly the incus. 



The remaining parts of the visceral skeleton form the hyoid 

 apparatus and embrace the branchial region in the fishes, furnishing 

 support for the gill arches, while in terrestrial classes their first 

 function continues and they are otherwise represented by the 

 cartilages of the lar>'nx and upper part of the trachea. 



The Appendicular Skeleton of Fishes. The appendicular 

 skeleton is simplest in the fishes. Since their bodies are buoyed 

 up at all points by the heavy medium in which they live, the 



