. The development of the chick; an introduction to embryology. Birds -- Embryology. THE SKELETON 437 small; the second, third, and fourth represent the persistent digits. In each ray is a membranous skeletal element, which, however, soon disappears in the first and fifth. Thus there are distinct indications of a pentadactyl stage in the development of the bird's wing. In the definitive skeleton there are but two carpal bones, viz., a radiale at the extremity of the radius, and an ulnare at the extremity of the ulna. In the embryo there is evidence of seven transitory pieces in the carpus arran
. The development of the chick; an introduction to embryology. Birds -- Embryology. THE SKELETON 437 small; the second, third, and fourth represent the persistent digits. In each ray is a membranous skeletal element, which, however, soon disappears in the first and fifth. Thus there are distinct indications of a pentadactyl stage in the development of the bird's wing. In the definitive skeleton there are but two carpal bones, viz., a radiale at the extremity of the radius, and an ulnare at the extremity of the ulna. In the embryo there is evidence of seven transitory pieces in the carpus arranged in two rows, proxi- mal and distal (Fig. 247). In the proximal row only two car- M' /'cA. -H M'c.^ Cp.^ Cp3 ^â¢^â P'c/). Fig. 247. â Skeleton of the wing of a chick embryo of 8 days. (After W. K. Parker.) Cp. 2, 3, and 4, Second, third, and fourth carpalia. C. U., Centralo- iilnare. H., Humerus. I. R., Intermedio-radiale. M'c. 2, 3, 4, Second, third, and fourth metacarpaha. P'ch., Perichondral bone R., Radius. U., Ulna. tilages appear, viz., the radiale and ulnare; but in earlier stages each appears to be derived from two centers: the radiale from a radiale and an intermedium, the ulnare from an ulnare and a centrale. Evidence of such double origin of each is found also in the cartilaginous condition (v. Parker, 1888). Four elements in all enter into the composition of this proximal row. In the distal row there are three distinct elements corresponding to the three persistent digits, and representing, therefore, carpalia II, III, and IV. These subsequently fuse with one another, and with the heads of the metacarpals to produce the carpo- metacarpus. On the seventh day the metacarpus is represented by three cartilages corresponding to the three persistent digits, viz., II,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not
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