The development of pneumatisation in the postcranial skeleton of the domestic fowl.
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In a flock of Golden Comet pullets, the entire vertebral column and ribs, coracoids, os coxae and humeri were examined from hatching to 182 days of age. No pneumatization was found until 35 days after hatching, when it had occurred in several vertebrae, number 14 being the last. The usual pattern of adult pneumatization, involving vertebrae 3-16, was present in most birds from 63 days after hatching. In all the birds there were five vertebrae in the thoracic and 15 in the synsacral region. Pneumatization was found only in vertebral ribs 1 and 2, in the body and keel of the sternum, in the humerus (where it increased to 80% of the length of the bone 112 days after hatching), but not at all in the coracoid or os coxae. Comparative studies in White Leghorn pullets and cockerels revealed regular pneumatization of the humerus from the time of onset (28 days) and the coracoid was frequently pneumatized. Rate of pneumatization was more rapid in this breed and, within the breed, more rapid in pullets than in cockerels.