16 
Fretp Museum or Naturat History — Zodrocy, Vor. XI. 
the terminal part) are collectively known as mesosternum, while the 
lower end is called xiphisternum, xiphoid, or ensiform process of the 
sternum (see chart, p. 11). The presternum is often ‘‘keeled,” 
having a ridge along the middle line below, noticeably in the Bats, 
which like the birds require support for a large pectoral muscle as 
an aid to flight. 
Scapula, generally a broad, flat bone commonly called the “shoulder 
blade,”’ which is present in all mammals. It has a median ridge on 
the outer surface which is called the “‘spine,”’ the projecting end of 
which is known as the acromion process. 
Clavicle or collar bone in Man articulates with the upper border of the 
sternum and the acromion process of the scapula. It is present 
and complete in some mammals, such as Primates (Man, Monkeys, 
Apes, etc.), Bats, Insectivores, and others; and appears in rudi- 
mentary form in others, such as most of the Carnivores, some 
Rodents, etc., but it is absent in Whales, Seals, Ungulates, some of 
the Bears, some Rodents, and others. 
The Limbs and Feet — All mammals, with the exception of some of the 
aquatic species such as Whales, Manatees, etc., have four limbs and 
for this reason are often called Quadrupeds. In the fore limbs the 
bone of the upper arm is called the humerus; the lower part of the 
arm or ‘‘fore arm”’ has two bones, the radius and ulna. The wrist 
or carpal joint consists of several bones, usually 5 to 8, known as the 
bones of the carpus. The bones of the hand are designated as 
metacarpals and those of the fingers, phalanges. 
As has already been stated, the hind limbs are lacking in aquatic 
species, such as the Whales and Manatees. In the former even the 
pelvis is rudimentary and is represented by two small detached 
bones not connected with the skeleton. The bones of the hind 
limbs are: Thigh, femur; lower leg bones, tibia and fibula; ankle joint, 
bones of the tarsus; bones of the foot, metatarsals; and toes, phalanges. 
The variation in the character and shape of the limbs and feet 
is very great, as illustrated by the “flippers” of a Seal, the feet of a 
Horse or those of a Lion, Deer, Sloth, Monkey, Mole, etc. In 
some species practically the whole sole of the foot touches the 
ground in walking; these are known as plantigrade. Others walk 
on their toes and are called digitigrade.* In the Horse, for example, 
the true heel is elevated a foot or more from the ground. 
In nearly all mammals { the terminal extremities of the digits are 
protected by hard epidermal structures in the form of claws, nails, and 
2 
* Intermediate types are often termed semi-plantigrade, unguligrade, etc 
+ Absent in the Whales, but rudiments have been found in the foetus 
