THE PECTORAL GIRDLE.--The skeleton by which the fore-limb is connected with the trunk is known as the Pectoral Girdle. The main part of this girdle is formed by the large scapula, or blade-bone as it is often termed. The coracoidal elements will be dealt with later. The scapula is not firmly connected with the backbone; it is attached merely by muscles, thus presenting a great difference from the corresponding pelvic girdle. The reason for this difference is not easy to understand. On the one hand it may be pointed out that in all running animals at any rate there is a greater need for the fixation in a particularly firm way of the hind-limbs; but, again, in the climbing creatures both limbs would, one might suppose, be bettered by a firm fixation. It must be remembered, however, that in the latter case the same result is at least partly brought about by a well-developed clavicle, which fixes the girdle to the sternum and so to the vertebral column by means of the ribs. Broadly speaking, too, the fore-limbs require a greater freedom and variety of movement than the hind-limbs, which are supports {36} for or serve to push along the rapidly-moving body. Stronger fixation is therefore a greater necessity posteriorly than anteriorly. In any case, whatever the explanation, this important difference exists. [Illustration] FIG. 25.--Right scapula of Dog (_Canis familiaris_). x 1/4. _a_, Acromion; _af_, prescapular fossa; _c_, coracoid; _cb_, coracoid or anterior border; _css_, indicates the position of the coraco-scapular suture, obliterated in adult animals by the complete ankylosis of the two bones; _gb_, glenoid or posterior border; _gc_, glenoid cavity; _pf_, postscapular fossa; _s_, spine; _ss_, suprascapular border. (From Flower's _Osteology_.) [Illustration] FIG. 26.--Right scapula of Red Deer (Cervus elaphus). x 1/4. _a_, Acromion; _af_, anterior or prescapular fossa; _c_, coracoid; _gc_, glenoid cavity; _pf_, postscapular fossa; _ss_, partially ossified suprascapular border. (From Flower's _Osteology_.) The shoulder-blade of mammals is as a rule a much-flattened bone with a ridge on the outer surface known as the spine; this ridge ends in a freely-projecting process, the acromion, from which a branch often arises known as the metacromion. This gives a bifurcate appearance to the end of the ridge. The spine is less developed and the scapula is narrower in such animals as the Dog and the Deer which simply run, and whose fore-limbs therefore are not endowed with the complexity of movement seen, for instance, in the Apes. {37} [Illustration] FIG. 27.--Right scapula of Dolphin (_Tursiops tursio_). x 1/4. _a_, Acromion; _af_, prescapular fossa; _c_, coracoid; _gc_, glenoid cavity; _pf_, postscapular fossa. (From Flower's _Osteology_.) [Illustration]