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Show 1873.] CERTAIN M U S C L E S O F B I R D S . 629 back of the leg superficially. A small part of the main muscle, the inner, goes straight forward to end at the inner side of the upper extremity of the tibia by a flat tendon ; but most of it joins the accessorius to be continued down the leg. Some birds, as the Eagles and Owls, have no semitendinosus at all; some, as the Anserine birds and Penguins, have no accessory simitendinosus, in which case all the fibres go straight to the tibia-head ; whilst in most the above-described condition maintains. Semimembranosus.-This ribbon muscle runs parallel to, deep of, and next to the semitendinosus. It arises from the outer border of the anterior margin of the ischium for about a third of an inch, at the place where it is in contact with the pubis, the origin extending down to the lower end of the slight prominence at the point where the ischium slightly overlaps the pubis. It is inserted along with the tibial end of the semitendinosus into the inner side of the head of the tibia by a broad flat thin tendon. This muscle is very constant in birds : in the Grebes it is extremely thin, and may sometimes be absent, as stated by Sundevall; but I have seen it in some fresh specimens of Podiceps minor, though but very slightly developed. Ambiens.-This peculiar, small, but very long muscle is triangular or fusiform in shape. It arises from the tip of the short anteriorly directed spine which is situated just above the anterior border of the acetabulum, and runs along the inner side of the thigh to the inner side of the knee, where it is covered by the sartorius, which is above it in the former part of its course. Its thin tendon then crosses the knee, running in the substance of the fascial extensor tendon, just in front of the patella, to the outer side, where it joins the fibres of origin of the flexor perforatus digitorum. Femoro-caudal.-This long ribbon muscle is covered superficially by the tensor fasciae and biceps above, as well as by the semitendinosus lower down. The sciatic artery and nerve cross it superficially at right angles close to its insertion as they course from the sciatic foramen, parallel to the femur, to the popliteal region. The femoral vein separates this muscle from the adductor muscles at their insertions, except in Dacelo, where it crosses the femoro-caudal superficially*. It arises from the (anterior) transverse processes of the two last coccygeal vertebrae, and is inserted into the linea aspera of the femur, at about one third its length from the trochanter. A n accessory head, arising from the upper three fourths of the postacetabular ridge, and from the ridge which forms the lower margin of the origin of the obturator externus, joins the tendon of insertion of this muscle, and is also partly inserted into the linea aspera, between it and the head of the femur. It is thin, muscular, and broad, covering the obturator externus superficially, and is partially intersected by a fibrous sheet where it crosses its anterior border. The sciatic artery and nerve cross it superficially; and the nerve to the semimembranosus is deep of it, whilst that to the semitendinosus is superficial in some cases ; the biceps completely covers it. Of the above-described muscles, five of them (the ambiens, the * In Centropus phasianus the main artery of the leg is also the femoral, and not the sciatic, as in other birds; it therefore runs with the femoral vein in that bird. |
