SKULL OF THE SLOTH. 198 



be turned round every part of a branch in quest of the \ 

 leafj food by this mechanism of the neck. As the trunk 

 is commonly suspended from the limbs with the back 

 downwards, the muscles destined for the movements of 

 the back and support of the head are feebly developed, 

 and the vertebral processes for their attachment are pro- 

 portionally short. The spines of the neck-vertebrae are 

 of more equal length than in most mammals — that of the 

 dentata being little larger than the rest: the spines gra- 

 dually subside in the posterior dorsals, and become 

 obsolete in the lumbar vertebras. The first pair of fully- \ 

 developed ribs, marking the beginning of the true " dorsal" j 

 series of vertebra, are anchylosed to the breast-bone i 

 v/hich consists of eight ossicles. In the two-toed sloth, | 

 however, which has twenty-three dorsal vertebrae, there 

 are as many as seventeen subcubical sternal bones in one 

 long row, Avith their angles truncated for the terminal 

 articulations of the sternal ribs, which are ossified. 



The skull of the sloth is chiefly remarkable for the 

 size, shape, and connections of the malar bone, Avhich is 

 freely suspended by its anterior attachment to the maxil- 

 lary and frontal, and bifurcates behind ; one division ex- 

 tending downwards, outside the lower jaw, the other 

 ascending above the free termination of the zygomatic 

 process of the squamosal. The premaxillary bone is 

 single and edentulous, being represented only by its 

 palatal portion completing the maxillary arch, but not 

 sending any processes upwards to the nasals. 



The skull in the toothless ant-eater chiefly forms a 

 long, slender, slightly-bent bony sheath for its still longer 

 and more slender tongue, the main instrument for ob- 

 taining its insect food. The mouth in the living animal 

 is a small orifice at the end of the tubular muzzle, just 

 17 



