TLMGraphic-THQuinn-JBaume

Fig. 20A, B. Scheme demonstrating structures involved in the interlocking of the tuberculate part of the FDL tendon with the plicated part of the flexor tendon sheath. Longitudinal section of digit II of the foot of Corvus brachyrhynchos. A Ungual phalanx extended. B Ungual phalanx flexed. Not depicted: (1) interphalangeal joint capsules; (2) extensor tendon on dorsum of digit; and (3) podotheca of claw. Note: (l) In flexion, the insertion of the FDL tendon shifts away from the interphalangeal joint and subterminal phalanx, bringing the distal part of the tendon into contact with the tendon sheath. (2) The ungual podothecal pad is compressed by the flexed claw, the pad being displaced dorsoproximad against the tendon sheath. Both these actions cause the tendon sheath plicae to be engaged with the tendon tubercles (see text). 3. The robust extensor and flexor elastic ligaments with the claw extended A and their attenuated form with the claw flexed B (see text), elas ext lig, elastic extensor ligament of claw; ext proc, extensor process of ungual phalanx; elas flex lig, elastic ligament of flexor tendon; flex proc, flexor process of ungual phalanx;flex shth, flexor tendon sheath with plicae; interpad, podothecal interpad; subcutfat, subcutaneous fatty tissue; tend FDL, tendon of M. flexor digitorum longus with tubercles; ung pod pad, ungual podothecal pad with papillae. Credit: T.H. Quinn, J. Baumel

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