. The development of the chick; an introduction to embryology . phalanges, itis naturally of considerable interest to learn how much of theancestral history is preserved in the embryology. The hand isrepresented in the embryo of six days V)y the s])atulate extremityof the foic-limb, which includ(-s the elements of carpus, meta-carpus, and phalanges. Ilom this expansion five digital raysgrow out sinudtaneously, th(> fiist and fifth V)eing relatively THE SKELETON 437 small; the second, third, and fourth represent the persistent each ray is a membranous skeletal element, which, howev
. The development of the chick; an introduction to embryology . phalanges, itis naturally of considerable interest to learn how much of theancestral history is preserved in the embryology. The hand isrepresented in the embryo of six days V)y the s])atulate extremityof the foic-limb, which includ(-s the elements of carpus, meta-carpus, and phalanges. Ilom this expansion five digital raysgrow out sinudtaneously, th(> fiist and fifth V)eing relatively THE SKELETON 437 small; the second, third, and fourth represent the persistent each ray is a membranous skeletal element, which, however,soon disappears in the first and fifth. Thus there are distinctindications of a pentadactyl stage in the development of thebirds wing. In the definitive skeleton there are but two carpal bones,viz., a radiale at the extremity of the radius, and an ulnare atthe extremity of the ulna. In the embryo there is evidence ofseven transitory pieces in the carpus arranged in two rows, proxi-mal and distal (Fig. 247). In the proximal row only two car- Pc/?. ^H Mc.^ Cp,4 C/)3 ^•^■ PcS. Fig. 247. — .Skeleton of the wing of a chick einl)ryo of 8 days. (After Parker.)Cp. 2, 3, and 4, Second, third, and fourth carpaha. C. U., Centralo-ulnare. H., Humerus. I. R., Intermedio-ratliale. Mc. 2, 3, 4, Second,third, and fourth metacarpaha. Pch., Perichondral lione R., , Ulna. tilages appear, viz., the radiale and ulnare; but in earlier stageseach appears to be derived from two centers: the radiale from aradiale and an intermedium, the ulnare from an ulnare a centrale. Evidence of such double origin of each is foimdalso in the cartilaginous condition {v. Parker, 1888). Fourelements in all enter into the composition of this proximal the distal row there are three distinct elements correspondingto the three persistent digits, and re])resenting, therefore, carpaliaII, III, and IV. These subsequently fuse with one another,and with the heads of the metac
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