. Elements of Comparative Anatomy. 480 COMPARATIVE ANATO]\IY. appendage as a large bone, wliicli forms a piece of about tlie same size as tbe rest of the appendage; tliis may be called tlie humerus. In Plesiosaurus two succeeding pieces, which in Ichthyosaurus are still indifferent, are also increased in size; these correspond to the fore- arm : radius and ulna; these are succeeded by two transverse rows of smaller pieces, which form a carpus, and these again by longer rows of bones, which represent the metacarpus and the phalanges of the fingers. The segmentation which affects the appendage a
. Elements of Comparative Anatomy. 480 COMPARATIVE ANATO]\IY. appendage as a large bone, wliicli forms a piece of about tlie same size as tbe rest of the appendage; tliis may be called tlie humerus. In Plesiosaurus two succeeding pieces, which in Ichthyosaurus are still indifferent, are also increased in size; these correspond to the fore- arm : radius and ulna; these are succeeded by two transverse rows of smaller pieces, which form a carpus, and these again by longer rows of bones, which represent the metacarpus and the phalanges of the fingers. The segmentation which affects the appendage after the stem and rays are broken up into several pieces, may here be seen in its different stages. The arrangements which are presented by the Amphibia are similar in character; for although one finger is atrophied, we can fill up the void by the aid of the arrange- ments seen in the hinder limb, where they are complete. The stem of the archiptery- gium must, therefore, be sought for in a lateral series of skeletal pieces, which ex- tends from the humerus, through the ulna to the fifth finger, and in the carpus con- sists of two pieces. The other skeletal pieces are arranged on these rays. One ray begins with the radius, and extends into the first finger. A second, third, and fourth begin in the carpus, and end in the second, third, and fourth fingers. The primitive carpus is therefore composed of ten pieces; five carpals carry the fingers, three are attached to the bones of the fore- arm ; these are the radial, intermedium, and ulnare; two centralia (cc) are enclosed by these two sets. The change in the function of this appendage is connected with a rotation of the humerus on its own axis, and this rotation may be observed in the individual development of higher forms. It brings about a difference in the position of the limb as compared with that of lower Fig. 265. Diagram of the fore-limb of an Amphi- bian. The dotted lines indicate the rays, which remain attached to
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