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Show 1889.] ANATOMY OF POLYBOROIDES. 79 I find an identical arrangement of these tendons in Circus maurus, and they appear to be exactly the same (judging from a M S . sketch by Forbes) in Spizaetus occipitalis and Aquila imperialis. In Milvago chimachima and in Haliaetus albicilla and Astur approx-imans (Forbes, MS.) the tendon is single, but there is a trace of the second tendon in a short fibrous slip which, arising from near the Fig. 1. Tensores patagii and other muscles of Polyboroides typicus. t.p.l, tensor patagii longus; t.p.br, tensor patagii brevis; Anc, anconeus; B, deltoid. (The dotted parts represent tendons in this and the following figure.) insertion on to the forearm of the tensor patagii tendon, ends upon the patagium. This tendinous band may, however, perhaps be considered as the equivalent of the tendon which in other Accipitres (v. infra) unites the tendon of the tensor patagii longus with that of the tensor patagii brevis at the insertion of the latter on to the forearm. In Gypohierax1 the tensor patagii brevis resembles that of Polyboroides except that the outermost of the two tendons near to the 1 Fiirbringer, TJntersuchungen z. Morph. und Syst. d. Vogel, pi. xxii. fig. 9. |