1882.] PROF. W. H. FLOWER ON THE EDENTATA. 361 
In tracing true affinities we must not look to these obviously 
adaptive characters, but to others of really deeper significance. 
To commence with the skeleton, one of the most striking characters 
by which the Myrmecophagide differ from ordinary mammals is 
the presence on the posterior dorsal and the lumbar vertebra of 
accessory articulating surfaces, in addition to the true zygapophyses 
common to all mammals, and causing a remarkable interlocking of 
the arches of these vertebrae. Such articulations are found equally 
well-developed in the Megatheriide and in the Dasypodide, and 
in a comparatively rudimentary state in the Bradypodide, especially 
in Bradypus’. 
The whole vertebral column of the Sloths, especially the dorsal 
and lumbar region, is poorly developed, evidently in relation to the 
subordinate function of the muscles attached to it. In the ordinary 
position the animal hangs below the branches of the trees in which 
it dwells, the trunk being merely slung between the two pairs of 
extremities ; progression is effected chiefly by the body being 
dragged along by the fore limbs; the hind legs, which usually take so 
active a part insupporting and propelling the trunk, aresmall and weak, 
andthe functions of walking, running, andjumpingare alike in abeyance. 
Hence all the processes of the vertebral column—the spinous, trans- 
verse, and accessory—are but feebly developed. The existence then, 
even in a rudimentary form, of these additional articulations is ex- 
tremely significant. It may almost be said that they prove that 
the Sloths are descended from animals in which they existed in a 
fully developed form. On the other hand, like as in some respects 
the vertebral column of Manis is to that of Myrmecophaga, not a 
trace of either of these articulations or of the processes on which they 
are situated are to be found in the former. ‘There is a strong inter- 
locking of the lumbar vertebrze ; but it is formed by the greatly curved 
form of the true zygapophyses, and not by the addition of any 
superadded parts. In Oryeteropus also they are entirely absent. 
On this ground alone we might be justified in assuming that the 
Old-World Edentates are not closely related to the American forms. 
Nothing can be more different than the characters of the sternum 
of Myrmecophaga and of Manis. In the former the numerous meso- 
sternal segments are small, laterally compressed, and articulated with 
each other and with the strongly ossified sternal ribs by synovial 
joints. In Manis the sternum is broad and flat, and the sternal 
ribs only partly ossified, and connected with it in the normal manner. 
In these characters, the Bradypodide, Megatheriide, and Dasy- 
pedide agree with the Anteaters, and Orycteropus is more nearly 
related to Manis. 
The gigantic post-Tertiary Edentates of the New World, Mega- 
therium and its allies, throw much light upon the close affinity of 
the Sloths and true Anteaters. By common consent they have been 
placed among the former when the order is divided into two divisions, 
and are spoken of as ‘‘Ground-Sloths;” yet in many important 
characters, perhaps in all those not relating to the functions of 
1 See ‘Osteology of Mammalia,’ 2nd edit., 1876, p. 55. 
