No. 2.] THE HARD PARTS OF THE MAMMALIA. 217 
than that of the earth. In the case of the Quadrumana the 
movements of the fore legs are much varied, but include many 
transverse strains. The use of these limbs in swinging the 
body in all directions when climbing, furnishes ample use for a 
clavicle, and cause sufficient to prevent its atrophy. 
5. THE PEetvic ARtH. 
Modifications of the pelvic arch in Mammalia are seen chiefly 
in the form of the ilium and the direction of the pubis. 
The ilium differs in regard to the expansion of its proximal 
part, and the consequent length of its crest. It is a narrow 
bone in Marsupialia and Rodentia, and is a little wider and more 
flattened in Carnivora. In Edentata and Quadrumana it is con- 
siderably expanded, but the greatest expansion is seen in the 
Ungulata which are not Taxeopoda. There is a direct relation 
between the form of the iliac plate and the weight that it has 
to bear. In the mammals with narrow ilium the abdominal 
viscera are light as a consequence of either relatively or ab- 
solutely small size. In the types with wide ilia, these bones 
support weight either (1) with the length of the crest; or (2) 
with the long axis of the plate; or (3) transversely to the long 
axis. In (1) the iliac crest supports the huge belly with elongate 
viscera, of the Proboscidia, Amblypoda, and Diplarthra, all 
herbivorous or omnivorous. In (2) the body is erect more or 
less of the time, and the weight of the viscera passes downwards 
into the pelvis, spreading laterally against the iliac plates. In 
the smaller Edentata this pressure is insignificant, or rarely 
felt ; but in the huge extinct forms of the order the Megatheriide, 
the customary attitude in feeding was, as Owen pointed out, 
obliquely erect, leaning against the trees, or reaching upwards 
to obtain their branches and foliage. In the Quadrumana, the 
most constantly erect species, man, has the most widely ex- 
panded ilia. In (3), the only representation is the family of the 
sloths. Here the ilia bear a part of the viscera, directly, as 
the animal hangs suspended from the limb of a tree. 
The only noteworthy peculiarity of the pubis is the posterior 
direction which it presents in the Edentata. This character is 
traceable to the semi-erect position of the ancestors of the 
