532 



URODELA 



[CH. 



bones originally dermal bones, like the pterygoid and palatine 

 bones in Urodela, in more completely ossified animals, such as the 

 Teleostei (and as we shall presently see in the higher Amphibia 

 also), have begun to eat into the subjacent cartilage and thus to 

 deserve the name of cartilage bones. 



The upper lip has tooth- 

 bearing premaxillary and 

 maxillary bones developed, 

 the lower has a dentary on 

 the outside of Meckel's car- 

 tilage and a splenial on the 

 inner. Above the maxilla there 

 is a small prefrontal bone. 



If we examine the skeleton 

 of the limbs we find that 

 the pectoral girdle consists of 

 two plates of cartilage which 

 slightly overlap in the mid- 

 ventral line. The lower half 

 of each is forked, the forks 

 being called precoracoidand 

 coracoid respectively. The 

 centre of each half of the 

 girdle has a hollow termed the 

 glenoid cavity for the articu- 

 lation of the arm. All around 

 the glenoid cavity the girdle 

 is converted into bone ; there 

 is a bone termed the scapula 

 above, and a coracoid bone 



below. The un ossified part 



FIG. 257. A. ventral, and B. lateral view c , u -, 



of the shoulder girdle and sternum of of the coracoid IS Simply 

 an old male Crested Newt, Molge cris- termed the coracoid carti- 

 tata x 3. After Parker. , m i . , 



lage. The upper part of the 



3. Cora- 



coid. 6. Sternum. bone is called the supra- 



scapula. It remains carti- 

 laginous, but is often calcified. The two coracoids are fastened 

 behind to a small median cartilage called the sternum. The 

 meaning of this will be discussed later. 



The manus has only four fingers, the thumb and the cor- 

 responding small bone in the wrist or carpus having disappeared 



