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Show 284 MR. F. G. PARSONS ON THE [Mar. 20, The intra-pelvic portion seems often to be wanting, in which case it is very difficult to define the muscle. In the Dipodidae it is continuous with the gluteus minimus (Dipus cegyptius). Among the Octodontidae it is found between the two layers of the folded gluteus minimus in Aulacodus and Capromys; in Myopotamus aud Octodon it is normal. In the Hystricidae it was not seen in Hystrix, but was present in Sphingurus. In the Chinchillidae it was not seen in Chinchilla, but was made out with some difficulty in Viscacha. In the Dasyproctidae it is large and well marked, partly overlapping the gluteus medius (Dasyprocta, Ccelogenys). In the Caviidae it rises from the sacrum, but is continuous with the posterior border of the gluteus minimus (Cavia cobaya, Ceredon rupestris). In all the Sciuromorpha examined it was present and normal, except in Castor, where it was not seen. Obturator Internus and Gemelli.-These muscles usually have the same origin as in Man, but they are inserted into the digital (trochanteric) fossa of the femur. The gemelli are large, especially the anterior one. W h e n the obturator internus is cut through a number of tendons are seen on its deep surface converging to the digital fossa ; this is well shown in Ccelogenys. In Castor canadensis the origin of the obturator internus and gemellus posterior was taken up by the great tail-muscles, so that the anterior gemellus was the only part of this group present. Obturator Externus.-In all the Eodents dissected, this muscle had the usual human attachments. Its insertion into the digital fossa is deep to that of the obturator internus. Quadratus Femoris.-The quadratus femoris rises from the outer side of the tuber ischii, and is inserted into tbe back of the femur midway between the great and small trochanters. In the Hystricomorpha it is usually inserted by a narrow tendon, but in Sphingurus and the Sciuromorpha the insertion is fleshy and the muscle quadrilateral. Biceps Femoris.-The biceps rises from the spines of the anterior caudal vertebrae and the fascia over the tail-muscles; also by a dee]) head from the tuber ischii. These two parts, as a rule, unite and are inserted into the outer side of the patella, and the fascia of the leg from the knee almost, if not quite, to the ankle. This arrangement obtains in all the Rodents dissected, with the following exceptions :-In Sphingurus the two parts remain distinct, the superficial or caudal portion being inserted into the outer side of the patella and ligamentum patellae, while the deep portion from the tuber ischii is joined by a slip from the posterior sacral vertebrae and is inserted into the fascia of the leg continuing the plane of insertion of the former part. In Erethizon dorsatus1 1 P. Z. S. 1882, p. 271. |