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Show 1876.] ANATOMY OF CHAUNA DERBIANA. 19.T 2. The presence or absence of a special muscular slip from the Biceps humeri to the Patagium. The biceps humeri, the main flexor of the arm, arises from the upper end of the coracoid bone, and from the upper portion of the flexor surface of the humerus. In certain birds this muscle sends off from its upper end a slender fusiform belly, which runs through the proximal portion of the patagium to join its marginal tendon near the middle of its course (Plate XIV. fig. 2). The presence or absence of this muscular fasciculus is a very constant character among closely allied birds. In the Table (p. 199) are recorded the names of all those birds in which, according to m y experience, it is to be found. The only Anomalogonatous birds in which I have seen it are the Caprimulgida. 3. The Area of Origin of the Obturator internus. It is not my intention on the present occasion to enter into the consideration of whether the muscle here called obturator internus is homologous with the same-named muscle in Mammalia; suffice it to say that it arises from the pelvic surface of the pubis and ischium, and ends by a tendon which is inserted into the outer surface of the head of the femur. In a large number of birds, on looking at the pelvic view of this muscle when undisturbed, its shape is seen to be an elongated oval, occupying the obturator fossa, and covering the line of junction of the ischium and pubis. In another large number of birds, instead of being oval it is triangular, its posterior fibres expanding in such a way as to cover most of the pelvic surface of the ischium. There are a few birds in which an intermediate condition is found; they are, however, very few. In most there is not the least difficulty in deciding whether the obturator internus is oval or triangular (compare Plate XV. figs. 1 and 2). From the Table (p. 199) the arrangement existing in most birds can be found. 4. The degree of Development of the Tensor-cruris fascia. To this point I have referred in m y paper on the muscles of Birds*, where its relations are explained. "It is the superficial muscle of the outside of the thigh, covering the femur. It is flat and triangular in shape, and arises as a membranous expansion which covers the gluteus ii., from the lower two thirds of the posterior border of the iliac fossa in which that muscle is situated, and from the fibrous septum which separates that muscle from the gluteus iii. Further down it has origin also from the whole length of the ridge which separates the postacetabular area from the external lateral surface of the ischium, and which may be termed the postacetabular ridge, as well as from the posterior border of the ischium, as far forwards as its junction with the pubis, being here slightly overlapped by the semitendinosus. The fibres converge towards the knee ; and the deep portion of the muscle blends in its course with the vastus externus, together with which it continues * P. Z. S. 1873, p. 628. 13* |