The skeleton of Desmostylus mirabilis from South Sakhalin

V. Limb bones

Abstract

The long limb bones of Desmostylus mirabilis NAGAO from Keton are re-described. The author considered that the description formerly done by SHIKAMA (1966) seems to be in adequate for the mounting skeleton, and he stated somewhat different idea in the evaluation of the morphological characteristics of each bone (Table 1). The common characteristics of the long limb bones of Desmostylus mirabilis are able to be summarized as being stout in general and associated with well-developed epiphyses. Other features are as follows: Humerus: head faced rather backward than upward; major tubercle in lower level than head, protruded foreward feebly; deltoid tuberosity small, projected laterally; body flat fore-and-aft for the width; medial trochlea larger than the lateral in diameter. Forearm: radius and ulna in nearly equal thickness; olecranon thick, bended backward; trochleal axis at right angles to the long axis of carpal articular surface; distal epiphysis well-developed with its articular surface inclined medially. Femur: head spherical, neck constricted clearly along its circumference; major trochanter in lower level than head; minor trochanter in low level, extended long distally; body bended outward, flat fore-and-aft; femoral trochlea hardly concave transversely; intercondylar fossa narrow. Tibia: tibial tuberosity developed remarkably; anterior margin slanted medially to the distal, its free margin leaned laterally in the proximal region; tarsal articular surface inclined anterolaterally.