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Show 178 MR. F* G. PARSONS ON THE [Jan. 14, Muscles of Posterior Extremity. Gluteus Maximus, Tensor Fasciae Femoris, and Sartorius.-The description already givenl applies perfectly to the Myomorpha; the tensor fasciae and sartorius are, however, as a rule less well marked, and there is also a closer union between the posterior border of the gluteus maximus and the anterior border of the biceps femoris. The bony insertion of the gluteus maximus is into the middle of the femur except in Cricetus, where it is also attached to the external supra-condylar ridge of the femur, and in Rhizomys, where it is attached almost entirely to the third trochanter in the upper part of the bone. The sartorius and tensor fasciae femoris are best marked in Cricetus, while in Georychus they are practically absent. Gluteus Medius and Minimus.-These muscles present no differences from those already described in other Rodents. Scansorius.-The scansorius is so closely fused with the gluteus minimus, that it is only possible to make it out as a distinct muscle in Cricetomys, though even there the separation is not very clear. Pyriformis.-This muscle is also much more closely fused with the gluteus minimus than in the other Rodents; indeed, the Myomorpha are remarkable for the unsatisfactory differentiation of the muscles composing the gluteal mass. Obturator Internus, Externus, and Gemelli.-These muscles correspond to their descriptions in the other Rodents. The anterior gemellus is always better marked than the posterior one. Quadratus Femoris.-There is usually a very slight tendon at the insertion, the muscle being triangular as in the Hystricomorpha and differing from the quadrilateral Sciuromorphine type; it is always large and distinct. Biceps Femoris.-In Myoxus, Mus barbarus, and Mus rattus the two parts of which the biceps is composed are closely united and have one continuous insertion, as is the case in the Hystricomorphine Rodents. In the other Myomorpha the two parts are easily separable, as they are in Sphingurus2. When this happens, it is the upper part which rises from the anterior caudal vertebrae and is inserted into the outer side of the patella and ligamentum patellae, while the lower part rises from the tuber ischii and is inserted into the fascia on the outer side of the leg. In certain cases, e. g. Cricetomys and Myodes, the upper portion is very closely connected to the gluteus maximus; while in Cricetus it is so closely blended with that muscle, that it has already been described as a part of the gluteus maximus which is inserted above the external condyle of the femur. In Georychus, Bathyergus, Rhizomys, and Heteromys the two parts are separate from one another and from the gluteal. 1 P.Z.S. 1894, p.282. 2 P.Z.S. 1894, p. 284. V |
