. The Cambridge natural history. Zoology. SKELETON 481 between them. They articulate with three carpal bones, the ulnare, intermedium, and radiale, while a small pisiform bone lies on the outer side, between the ulnare and the outer distal carpal bone. In Ichthyosaurus, from the Liassic period onwards, the ulna and radius are much shortened, broader than long, and touch each other without any intervening space ; the pisiform element is enlarged. Lastly. In Ophthalmosaurus of the Middle Oolite (but not in con- temporary species of Ichthyosaurus) the ulna and radius are still more reduced, and t
. The Cambridge natural history. Zoology. SKELETON 481 between them. They articulate with three carpal bones, the ulnare, intermedium, and radiale, while a small pisiform bone lies on the outer side, between the ulnare and the outer distal carpal bone. In Ichthyosaurus, from the Liassic period onwards, the ulna and radius are much shortened, broader than long, and touch each other without any intervening space ; the pisiform element is enlarged. Lastly. In Ophthalmosaurus of the Middle Oolite (but not in con- temporary species of Ichthyosaurus) the ulna and radius are still more reduced, and the pisiform has moved up to the humerus, so that the latter articulates with three ^m'-' n. Fig. 114.—A, Ventral view of the shoulder-girdle and right fore-limb of an Ichthyosaimis, from the Lias ; B, part of the fore-limb of a Mixosaurus, from the Trias ; C, part of the fore-limb of an Ophthalmosaurus, from the Chalk, c,, c^, first and second centrale carpi; CI, clavicle ; Co, coracoid ; H, humerus ; /, interclavicle ; i, inter- medium carpi; p, pisiform ; R, radius ; r, radial carpal; Sc, scapula; V, ulna; u, ulnar carpal. Other important features of these paddles are not only the much-increased number of phalanges (sometimes up to twenty or more), but also the increase of digits to six or more, produced apparently by a splitting of the third finger into two series, and by the development of additional rows of phalanx-like bones on the outer and inner margins of the paddle. This increase of fingers exists, for instance, in Ichthyosaurus communis, but not in I tenuirostris. Owing to this peculiar development of paddles the constituent bones are extremely numerous, and from the radius and ulna downwards they are all closely packed, and have assumed a polygonal, often hexagonal, shape, dwindling to more or VOL. VIII 2 ^. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
