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Show 1894.] ON THE FLEXOR MUSCLES IN BIRDS. 495 2. On the Perforated Flexor Muscles in some Birds. By P. CHALMERS MITCHELL, M.A., F.Z.S. [Received May 30, 1894.] However opinions may differ as to the value of muscles in classification, few would dispute that the ambiens muscle of birds, in the peculiarity and isolation of its position and course, and in the constancy of its relations, is an anatomical character difficult to overlook in classification. The ambiens, as all anatomists know from the researches of Grarrod, is a slender muscle which, after origin from a spine or ridge immediately in front of, or below, the acetabulum, runs along the inner side of the thigh to end in a thin tendon which usualiy crosses the knee and joins the flexor perforatus digitorum. Its presence and absence are associated with so many other peculiarities of structure that Grarrod divided all birds into the Homalogonatce, which possess the muscle in question, and the Anomcdogonatce, in which the ambiens is absent. While taking advantage of the abundant opportunities afforded by the laboratory in the Society's Gardens, by the kindness of my friend Mr. F. E. Beddard, the Society's Prosector, I have dissected the leg- and thigh-muscles iu the following birds:- Ba lea rica chrgsop ela rgus. Hcdiactus leucogaster. Psophia leucoptera. Thaumalea amherstice. Fulica leucoptera. Leptoptilus crumeniferus. Palamedea cornuta. Aramides ypecaha. Hcematopus ostralegus. Nycticorax gardeni. Eclectus roratus. Corvus capellanus. Bubo maximus. In the first nine of these the ambiens is present, and the relation of its tendon to the flexor perforatus digitorum is constant. In these, as in other birds which I have dissected, the perforated flexors lie immediately under the two " perforated and perforating " flexors, those of the second and third digits. Fig. 1 (p. 496), which I have drawn from a dissection of the Cape Crowned Crane, shows an arrangement wdiich is, in the main, typical of the other eight birds. Distally, the three tendons pass respectively to the second, third, and fourth toes. These tendons arise from a mass of muscle innervated by that branch of the ischiadic nerve that also supplies the middle head of the gastrocnemius muscle. The mass of muscle has three distinct origins-an inner head, which arises from the intercondylar notch very close to, and sometimes in common with, the head of the flexor longus hallucis • an outer head, from the outer condyle of the femur under and partly in common with the origins of the flexores perforati et perforantes, and from which a strong fibrous connection, sometimes double, ruus to the short arm of the biceps sling; and an ambiens head, sometimes fleshy, sometimes tendinous, from the tendon of the ambiens. From |
