79 



being complete in Choleepus, whilst it is only a rudimentary appendage in Bra- 

 dypus proper. 



The scapula of the Megatherium, while it exhibits the same essential charac- 

 ters as that of the Mylodon, differs very recognizably in the position of the 

 spine, which commences much nearer the lower angle, and, running parallel 

 with the inferior costa, leaves above it a much greater proportional extent of 

 supraspinal fossa, than in the Mylodon. The general configuration of the 

 scapula is different in the Megatherium : the base is straighter and relatively 

 longer ; the inferior costa relatively shorter ; the anterior border is longer, 

 especially below the glenoid cavity, so that the blade of the scapula in the Me- 

 gatherium presents almost the form of a trapezium, save that the greater extent 

 of the posterior border destroys the paralleUsm of the upper and lower borders. 

 The inferior and anterior angle of the scapula is bent outwards in the Mega- 

 therium, increasing the depth of the subspinal fossa. The ridge extending from 

 the inferior and posterior angle forwards upon the under surface of the scapula 

 is relatively stronger in the Megatherium, more abruptly terminated, and from 

 its lower position and the bending outwards of the inferior costa, it seems to 

 prolong the inferior surface of the scapula downwards, and, to the same extent, 

 gives the everted inferior costa the character of a second spine. As such a se- 

 cond spine, and the greater, prolongation of the blade-bone below it, is the 

 characteristic of the scapula in the Ant-eaters, this indication, although slight, 

 of the affinity of the Megatherioid quadrupeds to the Ant-eaters is not without 

 interest. 



Both the acromion and coracoid are relatively more produced in the Mega- 

 therium than in the Mylodon : the clavicular cavity is also deeper and more 

 irregular, indicating a hgamentous union of the bones. The glenoid cavity is a 

 broader ellipse. 



Compared with the scapula of the Scelidotherium, that of the Mylodon is also 

 more equally divided by the spine : it is evident from the remains of the inferior 

 costa, at the anterior part of the scapula, that the infraspinal fossa was of rela- 

 tively less extent in the SceUdo there. Both the superior costa and the base are 

 straighter in the Scehdothere, and the upper and posterior angle is less rounded. 

 The acromio-coracoid bridge is longer and narrower ; the clavicular cavity rela- 

 tively smaller, but of the same form and with a smooth surface. 



