XV. 
progression employed by various quadrupeds, according to the 
amount of palmar and plantar surfaces in contact with the 
ground; thus those, as the Bears, which use the whole of 
the lower surface of the carpus, metacarpus, and phalanges, 
are termed “plantigrade”; those, as the Horse, which apply the 
distal surface of the ungual phalanx and the horny structures 
surrounding it, “‘ wnguligrade”; intermediate forms exist, such 
as “nhalangigrade” for the Camel, and “subplantigrade” for 
most Carnivores. In the Bats the digits are enormously elongated 
for the purpose of supporting a cutaneous expansion constituting 
the organs of flight ; while in the Whales and Dolphins the manus 
is formed into a paddle, covered by continuous integument, and 
without any trace of nails or claws, and the number of phalanges 
belonging to the second and third digits always exceeds the 
normal number in Mammals, and sometimes very considerably. 
Posterior limb.—The posterior limb consists of a pelvic girdle, 
and three segments belonging to the limb. proper, the thigh 
(femur), the leg (tibia and fibula), and the foot (pes). 
Pelvic girdle.—The pelvic girdle is present in some form in all 
Mammals, but in the Sirenians and Cetaceans it is in a very 
rudimentary condition. Hach half of this girdle consists of three 
bones, which in the adult state are ankylosed together into a 
solid mass, and the single bone thus formed is technically known 
as the “os innominatum.” Of the three sections of which this 
bone is composed, the upper (z/iwm) is firmly articulated to the 
sacrum, and of the two lower, the antero-inferior (pubis) forms a 
symphysis with its fellow of the opposite side, except in the 
Insectivorous genera, Soricide, Talpide, and Chrysochloride, 
where these bones are entirely separated, while the postero- 
inferior /ischiwm) are never united. These three sections unite 
around a cup-shaped cavity, the acetabulum, into which the 
proximal end of the femur is received. Between the pubis and 
ischium there is a large opening known as the “‘obtwrator foramen.” 
The two innominate bones, in conjunction with the sacral, form 
the pelvis. By this direct articulation of the innominate bones 
with the vertebral column, greater strength is given to the 
hind limbs to increase their powers of supporting and propeling 
the body. In the Monotremes and Marsupials an additional 
pair of thin, flat, elongated bones, called the “ epipubie” or 
“marsupial” bones, the exact function of which is but im- 
perfectly understood, is attached to the fore part of the pubis, 
and projects forward into the muscular wall of the abdomen. 
Thigh and Ley.—As with the fore-limb, the proximal segment 
of the hind limb has but one bone, the femur, and the second 
two, the tibiw and the fibula ; these lie parallel to one another, 
the former, which is much the more strongly developed being on 
the inner side and more to the front, while the latter is on the 
outer side and behind. They are never either permanently 
