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Show 1896.] ANATOMY OF RHYNCHOPS. 301 Rhynchops shows a peculiar feature of Larus argentatus (cf. fig. 2) and of most Auks in the existence of these patagial tendons (A) on the ulnar side of the arm. In Rhynchops there are two instead of only one of these ; they run side by side obliquely, or really at right angles to the longus tendon when the wing is extended, and end upon the extensor metacarpi radialis muscle, on the inner side of the forearm ; the posterior of the two is inserted at a point Fig. 2. Patagial tendons of Larus argentatus (after a M S . sketch by the late W . A. Forbes). n, osseous nodule. Other lettering as in fig. 1. almost exactly corresponding with the insertion of the wristward slip of the brevis, though, as already said, on the opposite side of the arm. On the opposite wing I could find only a single tendon ; it was, however, very much longer, reaching further over the arm. The pectoralis muscle sends a slip to the patagial tendons, which is slightly differentiated from the rest of the pectoralis as a muscular belly: there is also a yellowish fibroid slip from the deltoid crest of the humerus. I could detect no biceps slip to the patagium on either wing. I looked, of course, very carefully for this muscle, as it is present in all the immediate allies of Rhynchops. The biceps is a very slender muscle which arises from the coracoid only. I found no trace of the missing humeral head. The muscle is divisible into two halves, the division commencing early in the slender tendon of origin. The outer of the two |
