Abstract
During the routine examination of chick embryos which had died during incubation, we found in 1923 several embryos exhibiting a striking abnormality resembling the condition known in mammals as Chondrodystrophia foetais (Kaufman).∗ As far as our knowledge of the literature reaches, chondrodystrophia is here reported for the first time in bird embryos.
The abnormal embryos were found first in the eggs from one fowl, but subsequently some 50 embryos of the same type have been found among about 4,000 embryos from several strains and varieties of fowls which have been examined. Inheritance may play some part in the causation of this abnormality, although our evidence is conclusive that it is not a simple Mendelian trait. Such embryos (at least those showing this malformation in a recognizable degree) have never hatched. Embryos dying as early as the 12th to 14th day of incubation have shown some of the extreme characters of the chondrodystrophic condition. Most frequently the abnormal embryos die near the end of the incubation period (18th to 20th days), while some have been found still living, but unable to emerge from the shell on the 23rd day of incubation.
The external morphology of these embryos, and, as far as our observations go, the histological structure of the cartilage and of the bones as well, resemble very strikingly the characteristics reported for mammalian chondrodystrophia. A typical chondrodystrophic embryo, nineteen days old, is shown in Fig. 1. A comparison of this embryo with a normal embryo of the same age (Fig. 2) shows at once the extraordinary shortening of the legs and the abnormal conformation of the head. In the most extreme cases the legs scarcely protrude beyond the body, the plantar surface is directed towards the body, and the legs are bent towards the body, but are too short to reach each other.
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