AN ANATOMICAL AND EMBRYOLOGICAL STUDY OF THE CLAVICLE IN CATS (FELIS-DOMESTUS) AND SHEEP (OVIS-ARIES) DURING THE PRENATAL PERIOD

The prenatal development of the clavicular area was studied in two spe cies: the domesticated sheep, which lacks a clavicle, and the cat, wit h a nonfunctional, rudimentary clavicle. A morphological and computeri zed morphometric study of the clavicle was performed in 18 cat embryos between 25 and 48 days of gestation, and in 12 sheep embryos of 37-45 days. One group of embryos was processed with double staining in tote according to Hanken and Wassersug in 1981. The other group was examin ed by histological techniques: hematoxylineosin-Alcian blue and picros irius. In both species, clavicular ossification is delayed (27% of ges tation time elapsed in sheep and 53% in cats) compared to 16% in human s, Histological and morphological differences in shape and length of t he clavicle were observed in both species, The clavicle is transient i n sheep, whereas in the cat it persists with little change. In neither species does secondary cartilage develop. In cats, the periosteum is well developed with active osteoblasts, whereas in sheep the clavicle is surrounded by a single layer of epitheloid cells and the periosteum is less developed and contains osteoclasts, These results suggest tha t the morphogenetic pattern for the clavicle is altered at about day 3 4 in cats and day 40 in sheep, and is subsequently partly inhibited in the former and blocked in the latter.