61 



of lumbar vertebrae with the pelvis, should be repeated separately, the one by an 

 existing, the other by an extinct species of the same natural tribe, and by no 

 other known mammalian animals. The figures of the skeleton of the Megathe- 

 rium by both Garriga and Pander show the three lumbar vertebrae as separate 

 bones ; and the first sacral vertebra in the pelvis in the College Museum presents 

 a free surface for hgamentous articulation on the anterior part of its body ; and 

 the left oblique process with its articular surface. In the Scelidotherium, like- 

 wise, the three lumbar vertebrae are unanchylosed. Two of the species of Myr- 

 mecophaga have three lumbar vertebrae ; the largest species {Myr. jubata) has 

 only two*. Not any of the other genera of Edentata have fewer than five lumbar 

 vertebrae. 



In the breadth of the ribs the Megatherioid animals resemble the Sloths and 

 the Edentata generally. This character is however exaggerated in the true Ant- 

 eaters, in which the vertebral ribs overlap each other. It is common to the 

 Ant-eaters, Pangolins, and Armadillos, with the Sloths, to have the cartilages 

 of the ribs ossified ; but only in the Myrmecophagae are the sternal ribs articu- 

 lated by double joints with the sternum. 



In the Sloths the sternal portion soon becomes anchylosed to the vertebral 

 portion, especially in the anterior ribs ; and the same thing happens in both the 

 Mylodon and Megatherium. 



Amongst extinct animals, the ribs of the Megatherium offer the nearest resem- 

 blance to those of the Mylodon, but with sufficiently recognizable distinctions. 

 The first rib is relatively shorter; its sternal partf is more expanded, and the 

 sternal articulation broader ; the anterior surface has not the longitudinal exca- 

 vation which the first rib of the Mylodon presents. 



The proximal or vertebral ends of the succeeding ribs present in the Megathe- 

 rium, as in the Mylodon, three distinct articular surfaces ; one terminal, subcir- 

 cular, and flat, for the body of the vertebra next in front ; the second on the 

 upper part of the head, horizontal, convex, oval, for the surface on the base of 



* In the skeleton of an aged individual of this species in the Museum of George LangstafF, Esq., 

 the last lumbar vertebra is anchylosed to the sacrum. 



f This rib offers no surface on its outer part for the attachment of the clavicle, as represented in 

 the figures of the Madrid skeleton, in which the anterior production of the manubrium is turned 

 backward. 



