. Bensley's Practical anatomy of the rabbit : an elementary laboratory text-book in mammalian anatomy. Rabbits -- Anatomy. THE APPENDICULAR SKELETON 61 chiefly for the strong development of the scapula as opposed to the weakness of the ventral, pectoral portion. In the rabbit the clavicle is vestigial, and in many mammals, such as the ungulates, it is entirely absent. In man, how- ever, as well as in other mammals in which the fore limb is capable of much movement transversely in- stead of only anteroposteriorly, the clavicle is well developed and is ar- ticulated at its ends with the scap- ul
. Bensley's Practical anatomy of the rabbit : an elementary laboratory text-book in mammalian anatomy. Rabbits -- Anatomy. THE APPENDICULAR SKELETON 61 chiefly for the strong development of the scapula as opposed to the weakness of the ventral, pectoral portion. In the rabbit the clavicle is vestigial, and in many mammals, such as the ungulates, it is entirely absent. In man, how- ever, as well as in other mammals in which the fore limb is capable of much movement transversely in- stead of only anteroposteriorly, the clavicle is well developed and is ar- ticulated at its ends with the scap- ula and sternum. In this condition it acts as a prop upon which the well-developed pectoral muscles of adduction move the limb. The absence of direct articulation with the vertebral column and the at- tachment thereto by muscles and ligaments provide a shock-absorb- ing apparatus which is of evident value in a quadruped, like the rab- bit, w^here locomotion is largely of a leaping character with the fore limbs reaching the ground first after each leap. Both pectoral and pelvic gir- dles in terrestrial vertebrates con- form more or less closely to a tri- radiate shape if the two halves are considered individually. The corresponding portions may be identified (Fig. 34), though in mammals the ventral portion in the case of the pectoral girdle is greatly reduced. Of the ventral elements, those commonly present in vertebrates are the coracoid, which forms the posterior ray, and the procoracoid, the anterior ray, the latter being partly covered in front by a derm splint, the clavicle. This condition, though not characteristic of mammals generally, is still found in monotremes and rudiments of the cora- coid extension ventrally are identifiable in embryonic marsupials. Adult marsupials and placentals show only a small hook-like. Fig. 34. Plan of the anterior limb skeleton in walking vertebrates, the equivalent elements of the posterior limb indicated in brackets: si, scapula (ilium), pp
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