. The development of the chick; an introduction to embryology . irds, and theelement ordinarily namedthe pubis as homologous tothe post-pubis of some rep-tiles. There is no evidencefor this in the spina iliaca develops asa cartilaginous outgrowth ofthe ilium and ossifies fromthe latter, not from an inde-pendent center (Mehnert). The Leg-skeleton. Theskeleton of the leg developsfi-om the axial mesenchyme,which is at first continuouswith the primordiura of thel)elvic girdle. In the processof chondrification it seg-ments into a larger numberof elements than found inthe adult, some
. The development of the chick; an introduction to embryology . irds, and theelement ordinarily namedthe pubis as homologous tothe post-pubis of some rep-tiles. There is no evidencefor this in the spina iliaca develops asa cartilaginous outgrowth ofthe ilium and ossifies fromthe latter, not from an inde-pendent center (Mehnert). The Leg-skeleton. Theskeleton of the leg developsfi-om the axial mesenchyme,which is at first continuouswith the primordiura of thel)elvic girdle. In the processof chondrification it seg-ments into a larger numberof elements than found inthe adult, some of which aresuppressed and others fusetogether. The digits growout from the jialate-like ex-pansion of tlie primitivelimb in the same fashion asin the wing. In general the separate elements arise in the ])roximo-distal order (Figs. 242 and 249). The femur rccjuires no spcM-ial descrii)tion: ossification ])egins on the niutli day. The priinordiuin of the fibula is from the first more slender than that of the tibia, thouiih relatively far larger than the adult. Fig. 24!). — Iliotofirapli of tlu skeletonof the leg of a chick emliryo of 15 daysincubation. Prepared by the potashmet hot!. (Preparation and photograjjhby Roy L. Moodie.)1, Tibia. 2, Filxila. :i, Patella. 4,Femur. 5, Ilium, (i, Pleurocentra ofsacral vertebrte. 7, Ischium. 8, , Tarsal ossification. 10, Second, third,and fourth metatarsals. 11, First meta-tarsal. I, II, III, IV, First, second, third,and fourtli digits. THE SKELETON 441 fibula. The fil)iilar cartilage extends the entire length of the cms,but ossification is confined largely to its proximal end; on thefourteenth day its lower half is represented by a thread-like fila-ment of bone. No separate tarsal elements are found in the adult; but in theembryo there are at least three cartilages,viz., a fibulare, tibiale and a large distalelement opposite the three main metatar-sals. In the course of development, thetwo proximal elements fuse with oneanother,
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