26. TARSUS, OR HOCK BONES.--The tarsus, or hock, corresponding to the ankle-joint of a man, is composed of six irregular compact bones, situated between the lower end of the tibia and the superior or upper extremity of the metatarsus; they are arranged in two series; one consisting of the cuboid and three cuneiform bones, the magnum, medium, and parvum, corresponds to the lower row or carpal bones; the other upper series consists of the astragalus and calcaneum; the first, forming with the bone above the mobile portion of the joint, may be said to correspond to the upper row of carpal bones, while the latter, being the lever bone, corresponds to the trapezium. These bones, like those of the carpus, are thickly covered with cartilage on their articular surfaces, which acts as a protection against concussion. It is these bones that become diseased and united when an animal is affected with bone spavin. The calcaneum bone which forms the prominent part, termed the point of the hock, and corresponds to the heel-bone of man. This bone gives attachment to the calcaneo-cuboid ligament, and it is this ligament that is sprained or ruptured in curb of the hock. 28. METATARSUS, OR OS METATARSI MAGNUM.--This bone presents the same general appearance as the large metacarpal or cannon bone, from which it differs principally in being about one-sixth longer and flattened from side to side. It is rounded and more prominent in front. This bone articulates above with the tarsus bones, and its lower portion articulates with the os suffraginis. 28. OSSA METATARSI PARVA, OR SPLINT BONES OF THE HIND LEG.--These also present the same general form as the small metacarpal bones of the front leg; the outer is the longest and largest, and has the largest head, with two surfaces which articulates with the cuboid bone; the inner one has also three articular surfaces, two for small, and one for the middle cuniform bones. The two surfaces on each head articulate with corresponding ones on the large metatarsal bone. The remaining bones of the hind extremity, viz.: the three phalanges, with their three accessory bones, so closely resemble the corresponding bones of the fore extremity, that it seems at first sight difficult to distinguish one from the other; the chief differences being, that the first phalanx of the hind extremity is longer; its upper end larger, and its lower end smaller, than in the fore extremity. COMPARATIVE OSTEOLOGY. In this section we shall endeavor to point out where the skeleton of the domesticated animals, other than the horse, differ from the typical skeleton of the latter in any important particular. The following descriptions are therefore in all cases comparisons, where comparison is possible, between the typical skeleton and the skeleton in question. RUMINANTIA. (Cud Chewing Animal.)