The Corpus fibule in Sheep (Ovis ammon f. aries) – its Ontogeny and Reduction or Persistence from Fetal Age to Adulthood

Abstract

The corpus fibulae (CF) in sheep is represented by a cartilaginous anlage during early embryogenesis, which may calcify and ossify with ongoing gestation and finally towards term is supposed to be replaced by a connective tissue cord called ligamentum fibulare (LF). A recent study in goat (Boos A and T Bartels, 2002), however, revealed that 58 % of the animals examined exhibited a pin‐shaped bone within the LF. This indicates that a complete transformation of the anlage of the CF to a connective tissue cord is not performed in all goats raising the question of existing parallels in sheep. Forty‐two fetuses and lower legs of 18 lambs and 100 sheep being elder than 2 years were collected at the slaughterhouse. Radiographs and macerated or enzymatically cleared and stained lower legs were assessed for the expression of a CF. In 28 of 42 fetuses (66%), 11 of 18 lambs (61%) and 48 of 100 adult sheep (48%) at least one cartilaginous – only fetal period – or osseous CF could be detected. Differences between groups were significant (Chi‐square test, P < 0.05). In 2, 3 and 15 animals, respectively, only a unilateral expression was evident. In early fetuses, the fibula either consisted of a long anlage having the length of the tibia or of a long proximal and a short distal part paralleling the tibia. In somewhat larger fetuses the CF was composed only of the proximal part or even completely lacked (crown rump length 7.5 ± 1.5 vs. 11.2 ± 2.4 and 12.2 ± 2.0 cm, respectively). Pre‐term fetuses, lambs and adult sheep were devoid of a CF (n = 5/7, 7/11 and 52/100, respectively) or exhibited a pin‐shaped bone of varying length within the LF. This osseous CF was either in close contact to the caput fibulae (n = 6 animals) – always separated by connective tissue – or located more distally. In the latter cases the centre of the osseous pin was usually situated at a level between the proximal and intermediate thirds of the tibia. Results suggest that the corpus fibulae in sheep may persist in many individuals (50%) as a pin‐shaped bone throughout life.Reference Boos, A., and T. Bartels, 2002: Ann. Anat. 184, 289–293