FIG. 28.--Side view of right half of shoulder girdle of a young Echidna (_Echidna hystrix_). x 2/3. _a_, Acromion; _c_, coracoid; _cb_, coracoid border; _cl_, clavicle; _css_, coraco-scapular suture; _ec_, epicoracoid; gb, glenoid border; _gc_, glenoid cavity; _ic_, interclavicle; _pf_, postscapular fossa; _ps_, presternum; _s_, spine; _ss_, suprascapular epiphysis; _ssf_, subscapular fossa. (From Flower's _Osteology_.) It has been pointed out that the area which lies in front of the spine, the prescapular lamina, is most extensively developed in such animals as perform complex movements with the fore-limbs. The Sea Lion and the Great Anteater are cited by Professor G. B. Howes as examples of this preponderance of the anterior portion of the scapula over that which lies behind the spine. The general shape of the scapula varies considerably among the different orders of mammals; but it always presents the characters mentioned, which are nowhere seen among the Sauropsida except among certain Anomodonts, which will be duly referred to (see p. 90). The most conspicuous divergences from the normal are to be found in the Cetacea and the Monotremata. In the former the acromion is approximated so nearly to the anterior border of the blade-bone that the prescapular fossa is reduced to a very small area; and in _Platanista_ the acromion actually coincides with the anterior border, so that that fossa actually disappears. In the Whales, too, the scapula is as a rule very broad, especially above; it has frequently a fan-like contour. In the Monotremata the acromion also coincides with the anterior border of the scapula; but the sameness of appearance which it thus presents (in this feature) to the Cetacean scapula is {38} apparently not due to real resemblance. What has happened in the Monotremata is, that the prescapular fossa is so enormously expanded that it occupies the whole of the inner side of the blade-bone, while the subscapular fossa which, so to speak, should occupy that situation, has been thus pushed round to the front, where it is divided from the postscapular fossa by a slight ridge only. The clavicle is a bone which varies much in mammals. It is sometimes indeed, as in the Ungulata, entirely absent; in other forms it shows varying degrees of retrocession in importance; it is only in climbing, burrowing, digging, and flying mammals that it is really well developed. [Illustration] FIG. 29.--Shoulder girdle, with upper end of sternum (inner surface) of Shrew (_Sorex_), after Parker, x 7. _a_, Acromion; _c_, coracoid; _cl_, clavicle; _ec_, partially ossified "epicoracoid" of Parker, or rudiment of the sternal extremity of the coracoid; ''ma'', metacromial process; _mss_, ossified "mesoscapular segment"; _ost_, omosternum; _pc_, rudiment of precoracoid (Parker); _ps_, presternum; _sr_^1, first sternal rib; _sr_^2, second sternal rib. (From Flower's _Osteology_.)