476 RIBS AND STERNUM.—BONES OF SHOULDER. 
connected with the cartilage of the seventh rib; while the 
other two ribs, being completely unattached at the anterior 
ends, are termed floating ribs. The sternum or breast-bone 
is flat and of simple form in Man; but it is much larger in 
many other animals. In those which have need of great 
strength in the upper limbs, such as Birds, Bats, and Moles, 
it is not only increased in breadth, but is furnished with a 
projecting keel or ridge for the attachment of powerful muscles 
(fig. 250). In the Turtle tribe, on the contrary, it is very 
much extended on the sides, so as to afford, with the ribs, a 
complete protection to the contained parts (§ 83). 
634. We have next to consider the structure of the member: 
or appendages which are attached to*this central framework. 
These are spoken-of as superior and inferior, when we are 
treating of Man, whose erect posture places one pair above 
the other: but when the ordinary Quadrupeds are alluded to, 
they are termed anterior and posterior, one pair being in front 
of the other. Each member consists of a set of movable 
bones, which serve as levers; but the socket in which the 
first of these works, is formed by a bony framework, which is 
connected more or less closely with the spinal column. This 
framework, in the upper extremity, consists of the Scapula 
or blade-bone, and the Clavicle or collar-bone. In the lowe 
extremity, it is formed by a set of bones, the union of which 
with the sacrum completes the Pelvis or bason at the bottom 
of the spinal column (fig. 223). 
635. The Scapula is a large flat bone, which occupies the 
upper and external! part of the back. Its form is somewhat 
triangular ; and at its upper and outer angle is a broad but 
shallow cavity, destined to receive the head of the humerus 
or arm-bone. Above this cavity is a large projection, termed 
the acromion-process, which is united by ligaments, &c., with 
the external end of the clavicle, and thus forms the bony 
eminence that we feel at the top of the shoulder. A little 
internally to this we find another process, the coracoid, which 
only serves in Man for the attachment of certain muscles, but 
which in Birds is developed into a distinct bone (§ 668). 
The hinder surface of the scapula is divided into two by a 
projecting ridge or keel, which gives a more extensive and 
1 The term external is continually used in Anatomy, to describe the 
parts furthest removed from the central or median line of the body. 
