. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. PECTORAL ARCH. 91 Fu(Cl), for its relations to the rest of the pectoral arch and to the sternum). Amongst the Cursorial Birds, the Emeu (DromaBiis) and Casso- wary (Casuarius) possess rudimentary clavicles: in the others they are wanting. In Archseopteryx, the scapular region only of the pectoral arch has been satisfactorily made out, and this resembles that of existing Birds. Mammals.—In Monotremes only amongst Mammals does the coracoid extend ventrally to reach the sternum ; in all the others
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. PECTORAL ARCH. 91 Fu(Cl), for its relations to the rest of the pectoral arch and to the sternum). Amongst the Cursorial Birds, the Emeu (DromaBiis) and Casso- wary (Casuarius) possess rudimentary clavicles: in the others they are wanting. In Archseopteryx, the scapular region only of the pectoral arch has been satisfactorily made out, and this resembles that of existing Birds. Mammals.—In Monotremes only amongst Mammals does the coracoid extend ventrally to reach the sternum ; in all the others it becomes reduced, and simply forms a prominent process on the scapula (coracoid process), which becomes ossified from a. FIG. 75.—PECTORAL ARCH OF Ornithorhynchus paradoxus. Sf, sternum ; Ep, inter-clavicle ; Co, coracoid ; Co\ epicoracoid ; S, scapula ; Of, clavicle ; G, glenoid cavity. separate centre. Thus the scapula alone serves to support the extremity; it becomes at the same time greatly broadened out, and gives rise on its outer side—in connection with the highly differentiated muscles of the limb—to a strong ridge (spina scapulae), which extends downwards to form the so-called acromion. The distal end of the clavicle usually becomes connected with the acromion, its proximal end articulating with the anterior edge of the sternum. In those Mammals in which the fore-limhs are capable of very varied and free movements, the clavicles are very strongly developed. In others, such as the Carnivora and Ungulata, they may he entirely wanting or only rudimentary, and in the latter case their relations to the scapula become Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wiedersheim, Robert, 1848-1923; Parker, W. N. (William Newton), d. 1923. London, New York, Macmillan
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