Anatomical features of the breast bone of the Baikal nerpa

Abstract

The breast bone forms the lower limits of the chest, where, under the influence of inspiratory muscles, it moves down, and expiratory muscles - up. During land travel, kinetic energy is absorbed through the breast bone. In the available literature, there are descriptions of the breast bone in some mammals, however, in the Baikal seal, the data require additional clarification. The material was sternum from Baikal seals aged from 6 months to 11 years (n=7). In the course of the study, the specific features of the morphology of the sternum of the Baikal seal in the age aspect were established. In particular, the sternum is formed from the handle, seven body segments, the xiphoid process and well-defined cartilages (the handle and the xiphoid process). The value of the length of the breast bone increases 1.4 times with age and is 47.7 ± 1.87 cm. Features of the morphology of the cartilaginous structures of the sternum, create mobility in its cranial part, and maximum strength between the 7th segment and the xiphoid process. The cartilage of the handle at the base is expanded, with age it undergoes ossification. In kumutkans, it is 68.4±2.33 mm long, 13.1±1.09 mm wide and 5.8±0.13 mm thick; by the age of mature seals, these values increased 1.6 times, 1.8 and 1.9 times, respectively. The segments of the thoracic bone body have a prismatic shape with rounded edges, and on the surfaces from the 3rd-4^th cranial ends of the segments and from the 1^st (2nd) to the 7th caudal ends, the presence of a pronounced median furrow is noted. On the xiphoid process, two pits and a protruding dorsally ridge stand out, and its cartilage has a pronounced pedicle, which caudally turns into a rounded plate.