The ulnar or fibular side of the carpus or tarsus becomes divided into a proximal element—the ulnare or fibulare—the ulnare remaining partially united with the intermedium. There are also formed from this plate two carpals to articulate with digits 3 and 4; while in the foot the corresponding elements articulate respectively with the third digit, and with the fourth and fifth digits.

Götte, whose observations were made in a somewhat different method to those of Strasser, is at variance with him on several points. He finds that the primitive skeleton of the limb consists of a basal portion, the humerus, continued into a radial and an ulnar ray, which are respectively prolonged into the two first digits. The two rays next coalesce at the base of the fingers to form the carpus, and thus the division of the limb into the brachium, antebrachium and manus is effected.

The ulna, which is primitively prolonged into the second digit, is subsequently separated from it and is prolonged into the third; from the side of the part of the carpus connecting the ulna with the third digit the fourth digit is eventually budded out, and in the foot the fourth and fifth digits arise from the corresponding region. Each of the three columns connected respectively with the first, second, and third digits becomes divided into three successive carpal bones, so that Götte holds the skeleton of the hand or foot to be formed of a proximal, a middle, and a distal row of carpal bones each containing potentially three elements. The proximal row is formed of the radiale, intermedium and ulnare; the middle row of carpal 1, the centrale and carpal 4, and the distal of carpal 2 (consisting according to Götte of two coalesced elements) and carpal 3.

The derivation of the cheiropterygium from the ichthyopterygium. All anatomists are agreed that the limbs of the higher Vertebrata are derived from those of Fishes, but the gulf between the two types of limbs is so great that there is room for a very great diversity of opinion as to the mode of evolution of the cheiropterygium. The most important speculations on the subject are those of Gegenbaur and Huxley.

Gegenbaur holds that the cheiropterygium is derived from a uniserial piscine limb, and that it consists of a primitive stem, to which a series of lateral rays are attached on one (the radial) side; while Huxley holds that the cheiropterygium is derived from a biserial piscine limb by the “lengthening of the axial skeleton, accompanied by the removal of its distal elements further away from the shoulder-girdle and by a diminution in the number of the rays.”

Neither of these theories is founded upon ontology, and the only ontological evidence we have which bears on this question is that above recorded with reference to the development of the Urodele limb.

Without holding that this evidence can be considered as in any way conclusive, its tendency would appear to me to be in favour of regarding the cheiropterygium as derived from a uniserial type of fin. The humerus or femur would appear to be the basipterygial bars (metapterygium), which have become directed outwards instead of retaining their original position parallel to the length of the body at the base of the fin. The anterior (proximal) fin-rays and the pro- and mesopterygium must be supposed to have become aborted, while the radius or ulna, and tibia or fibula are two posterior fin-rays (probably each representing several coalesced rays like the pro- and mesopterygium) which support at their distal extremities more numerous fin-rays consisting of the rows of carpal and tarsal bones.

This view of the cheiropterygium corresponds in some respects with that put forward by Götte as a result of his investigations on the development of the Urodele limbs, though in other respects it is very different. A difficulty of this view is the fact that it involves our supposing that the radial edge of the limb corresponds with the metapterygial edge of the piscine fin. The difficulties of this position have been clearly pointed out by Huxley, but the fact that in the primitive position of the Urodele limbs the radius is ventral and the ulna dorsal shews that this difficulty is not insuperable, in that it is easy to conceive the radial border of the fin to have become rotated from its primitive Elasmobranch position into the vertical position it occupies in the embryos of the Urodela, and then to have been further rotated from this position into that which it occupies in the adult Urodela and in all higher forms.

Bibliography of the Limbs.

(477) M. v. Davidoff. “Beiträge z. vergleich. Anat. d. hinteren Gliedmaassen d. Fische I.” Morphol. Jahrbuch, Vol. V. 1879.
(478) C. Gegenbaur. Untersuchungen z. vergleich. Anat. d. Wirbelthiere. Leipzig, 1864-5. Erstes Heft. Carpus u. Tarsus. Zweites Heft. Brustflosse d. Fische.
(479) C. Gegenbaur. “Ueb. d. Skelet d. Gliedmaassen d. Wirbelthiere im Allgemeinen u. d. Hintergliedmaassen d. Selachier insbesondere.” Jenaische Zeitschrift, Vol. V. 1870.
(480) C. Gegenbaur. “Ueb. d. Archipterygium.” Jenaische Zeitschrift, Vol. VII. 1873.
(481) C. Gegenbaur. “Zur Morphologie d. Gliedmaassen d. Wirbelthiere.” Morphologisches Jahrbuch, Vol. II. 1876.
(482) A. Götte. Ueb. Entwick. u. Regeneration d. Gliedmaassenskelets d. Molche. Leipzig, 1879.
(483) T. H. Huxley. “On Ceratodus Forsteri, with some observations on the classification of Fishes.” Proc. Zool. Soc. 1876.
(484) St George Mivart. “On the Fins of Elasmobranchii.” Zoological Trans., Vol. X.
(485) A. Rosenberg. “Ueb. d. Entwick. d. Extremitäten-Skelets bei einigen d. Reduction ihrer Gliedmaassen charakterisirten Wirbelthieren.” Zeit. f. wiss. Zool., Vol. XXIII. 1873.
(486) E. Rosenberg. “Ueb. d. Entwick. d. Wirbelsäule u. d. centrale carpi d. Menschen.” Morphologisches Jahrbuch, Vol. I. 1875.
(487) H. Strasser. “Z. Entwick. d. Extremitätenknorpel bei Salamandern u. Tritonen.” Morphologisches Jahrbuch, Vol. V. 1879.
(488) G. ’Swirski. Untersuch. üb. d. Entwick. d. Schultergürtels u. d. Skelets d. Brustflosse d. Hechts. Inaug. Diss. Dorpat, 1880.
(489) J. K. Thacker. “Median and paired fins. A contribution to the history of the Vertebrate limbs.” Trans. of the Connecticut Acad., Vol. III. 1877.
(490) J. K. Thacker. “Ventral fins of Ganoids.” Trans. of the Connecticut Acad., Vol. IV. 1877.