266 FOSSIL REPTILES. 



the second rib. Sometimes in this hgament are one, or even 

 two particular little bones. One of these bones is at first a 

 little cylindrical. It goes forward, and after having given from 

 its external face a portion of the articalary facet which re- 

 ceives the head of the humerus, it goes, making a greater or 

 less inflexion internally, to attach its other extremity to the 

 internal face of the sternum. The rest of the facet for the 

 articulation of the humerus is furnished by another bone, 

 which goes back more or less obliquely, and towards the cen- 

 tral line, widening like a fan. This remains nearly parallel to 

 the sternum. 



All the muscles which proceed to the arm are respectively 

 the same as in birds, whatever changes may take place in their 

 position relatively to the horizon, and in their size and figure. 



The existence of a clavicle is doubtful. A shoulder with 

 three branches, an omoplate nearly cylindrical, an acromial 

 portion nearly equal in volume to the rest of the omoplate, are 

 characteristic of the tortoises. There is nothing similar in 

 other animals, because in no other is the shoulder within the 

 thorax. Their varied forms present very good characters for 

 distinguishing the subgenera. 



In the sea-tortoises, that part of the omoplate which forms 

 the articulary face, is detached in some sort from the bone, 

 and forms a lateral apophysis ; and the two branches at the 

 re-entering angle which they form together are compressed, 

 broad and flat. The acromium is compressed, but in another 

 direction, and the coracoid bone is very long and not very 

 wide at its sternal extremity. 



In the land-tortoises, in which the dorsal buckler, being more 

 raised, gives more room for the extension of the omoplate and 

 its acromium, the angle is more open and the bone less com- 

 pressed. The coracoid is short, and so widened, that its ster- 

 nal edge is equal to its length. 



The shoulder of the fresh- water tortoises is a sort of medium 

 between these two. The coracoid bone is more long than 



