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Show 408 MR. ST. GEORGE MIVART AND DR. J. MURIE [June 26, part very intimately united (figs. 4 & 5, B.). The anterior portion arises from the sacral vertebrae, and is strongly muscular at its origin; superficially fibres pass on to the outside of the heads of the tibia and fibula, mingling with those of the broader second portion ; but deeply this portion of the muscle terminates in a flat, thin and narrow tendon, which is inserted into the outer side of the patella. The second portion originates by a very strong but short tendon from the outer side of the tuberosity of the ischium, and, expanding into a broad sheet of muscle, is inserted by aponeurosis into the outside of the leg down to the ankle. It thus seems that the tensor vaginae femoris, gluteus maximus, and the two parts of the biceps form together an almost continuous investment or sheet of muscle from the crest of the ilium to the caudal vertebrae and ischium, and from the patella to the ankle: together most powerfully flexing the limb. In the Guinea-pig the arrangement is very similar, except that the two parts are rather more distinct and that the anterior portion is narrower. In the Hare the two parts are very distinct, and the tendon of the anterior portion to the patella is much stronger and longer. The posterior portion presents no essential difference in attachments ; but the muscular sheet, which in the two former animals extends to the ankle, in the Hare is much more aponeurotic. The semimembranosus, unlike the condition of this muscle in Hyrax *, arises singly ; but it agrees in being an uncommonly large muscle. It has origin from the whole of the triangular space (or tuberosity) of the ischium, and is inserted broadly from the inner condyle of the femur to the head of the tibia (fig. 4, S. m.). A slight dissection, moreover, shows a division at its insertion into three portions, as in Man. The middle one is more or less formed by a distinct round and strong tendon, which springs from a separate belly of muscle more or less surrounded and enclosed by the rest of the semimembranosus. In the Guinea-pig, Hare, and Rabbit this separation, as it were, into two muscles is more strongly marked ; in the two last the fleshy insertion of the largest portion into the tibia is not so extensive as in the Agouti and Guinea-pig. It is relatively very large in the latter. Semitendinosus. Strong and bulky, it has two origins. The first arises by fleshy fibres from the caudal vertebrae as far back as opposite the tuberosity of the ischium, the fibres adhering to the deep fascia in the interspace between these two points. A second head, much smaller than the preceding, but also muscular, comes from the tuberosity of the ischium, and immediately joins the larger head. The anterior border of the first head is closely adherent to the posterior border of the gluteus maximus. Insertion: by a broad translucent strong sheet of tendon the whole length of the shaft of the tibia to os calcis (figs. 4 & 5, St.), as mentioned on the opposite page in the description of the gracilis. * P. Z. S. 1865, p. 347. |