OCR Text |
Show 180 MR. F. G. PARSONS ON THE [Jan. 14. and Bathyergus the straight head was reduced to a minimum; the reflected head has usually some fleshy fibres rising directly from it. With regard to the other muscles the vastus externus is large and separate, while the internus is small and closely blended with the crureus. Adductors.-The adductor mass in the Myomorpha resembles in its complexity that of the Sciuromorpha, although one frequently finds attempts at the more simple arrangement of the Hystrico-morpha by fusion or non-differentiation of contiguous parts. As in the other Rodents, the supracondylar slip has been described with the semimembranosus, to which it undoubtedly belongs. Perhaps the animal which shows the greatest differentiation is Cricetomys: in it the mass consists of the following parts:-(1) The most anterior portion from the ilio-pectineal line to the middle of the posterior border of the femur by a narrow flat tendon. (2) Deep to this is another bundle which has the same origin but comes from rather more of the symphysis and goes to the whole of the femur as low as the ligamentum patellae. (3) Behind the last is a thin flat portion rising by tendon from the horizontal ramus and being inserted into the lower half of the femur. (4) Most posteriorly, there is a thick mass from the ramus and tuber ischii which is inserted into the whole length of the back of the femur from the insertion of the quadratus femoris to the internal condyle. In Cricetus (1) and (2) are fused and (4) only goes to the upper half of the femur. In Microtus (1) and (2) are fused, as are also (3) and (4). In Gerbillus, Mus barbarus, and Mus rattus (3) was not identified, while (4) was only inserted into the upper half to two-thirds of the femur. Rhizomys closely resembles Cricetomys. In Georychus and Bathyergus (1) is inserted into the middle third of the femur behind the pectineus, while the other three parts are fused into one great mass, which in Georychus is inserted into the middle two-fourths of the back of the femur, while in Bathyergus it goes to the whole length of that bone. In Hydromys, according to Windle, the adductor magnus, which apparently corresponds to the part which I have described as (4), reaches as low as the head of the tibia l. Tibialis Anticus.-This muscle always has the human origin; it never rises from the femur as in some of the Hystricomorpha. In Georychus the tibia above the cnemial crest is flattened, and forms a triangle with the apex downward and the surface a little concave; from this the muscle rises. As a rule, the tendon divides slightly below to be inserted into the internal cuneiform and the base of the first metatarsal, the latter insertion being the smaller. In Microtus, however, the tendon divides into two equal parts. In Gerbillus, Mus barbarus, Mus rattus, and Myodes the tendon does not divide at all, but goes entirely to the cuneiform. In Heteromys the division is well marked, but both parts are inserted into the cuneiform. ...::... 1 P.Z.S. 1887, p. 58, ' |