| OCR Text |
Show 268 MESSRS. B. C. A. WINDLE AND F. G. PARSONS ON [Nov. 3, the delamination of the gluteal mass is not nearly so complete as it is in Man. In the Pig (4, 5, 8, 9, 11, 14), O x (35, 36, 38), and Sheep (41, 42, 43, 46, 47) the pyriformis is so completely fused with the meso- or entogluteus that no trace of it can be found. In no case does it come out of the great sciatic foramen, for this is closed by a membrane, and when the muscle is distinct it rises from the surface of this. The nerve-supply in the Duiker-bok and Harnessed Antelope is the superior gluteal. Obturator internus.-This muscle in the Suidas (4, 8, 11, 14), TragulidaB (20, 21), Giraffida? (32-34), Bovida? (36, 39, 41, 46, 48, 50, 53, 54, 55), and Procaviidse (74, 75) is small, and more nearly resembles a gemellus than the usual mammalian obturator internus : the reason for this is that the obturator tertius usurps the normal origin of the muscle, and the internus has to arise from the body of the ischium at the lesser sciatic notch, thus reverting to what is probably the original and generalised origin. Of its arrangement in the Cervidse we are not sure, but Watson and Young describe it in the Elk ( X X X . & XXXI.) as having the usual origin from the inner side of the obturator membrane. In the Perissodactyla and Elephantidse the muscle rises from the inner side of the true pelvis as usual. In all cases it is inserted into the bottom of the trochanteric (digital) fossa, and it is supplied by a branch of the sacral plexus. Gemelli.-In those animals just mentioned in which the obturator internus rises at the lesser sacro-sciatic notch, the gemelli are fused with it; in the others only an inferior gemellus is as a rule present. In the Horse, however (63, 65), three gemelli are often met with, the third rising a little ventral and caudal to the inferior, between it and the obturator externus. In the Elk (30) the two gemelli are joined. Obturator externus and Obturator tertius (see text-figs. 25 & 26).- Mivart and Murie nearly forty years ago described a muscle in Hyrax (74) passing through the obturator foramen and being inserted into the trochanteric fossa with the obturator externus; this they named the obturator tertius. Later Murie found the same muscle in the Giraffe (33),and Lesbres (V.) has evidently noticed the same thing, for he says that, in the Horse, Pig, and Ruminants, part of the obturator internus rises from the pelvis above the obturator vessels as high up as the ilium, while the other part passes through the obturator foramen. W e have carefully studied this muscle in the Chevrotain, Ox, Sheep, Goat, Pig, Duiker-bok, Harnessed Antelope, and Hyrax, and are convinced that the following is the explanation of it. The obturator tertius is really a part of the obturator externus, which has made its way through the obturator foramen from outside, pushing the obturator membrane in front of it. In doing this it has stolen a good deal of the usual origin of the obturator internus and pushed that muscle out of the pelvis, so that it rises, as we have shown, from the margin of the lesser sciatic notch. There is, therefore, the curious paradox of the obturator externus rising inside the pelvis, while the internus |
