180 ^i«. f. G. PAESONS 6n the [Jan. 14. 



and Bathyenjxis 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 tlie 

 crureus. 



Adductors. — The adductor mass in the Myoraorpha resembles in 

 its complexity that of the Sciiiromorpha, 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 

 Gricetomys; 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 patellee. (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 aud 

 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 Ci-ieetus (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) aud (4). In Gerbillus, Mus larbcirus, and Mus rattus (3) was 

 not identified, while (4) was only inserted into the upper half to 

 two-thirds of the femur, llldzomys closely resembles Gricetomys. 

 In Qeorychus 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 Oeori/chus is inserted into the 

 middle two-fourths of the back of the femur, while in Duthyergus 

 it goes to the whole length of that bone. In Hydromys, according 

 to Windle, the adducior magnus, which apparently corresponds 

 to the part which I have described as (4), reaches as low as the 

 head of the tibia '. 



Tibialis Anticus. — This muscle always has the human origin ; it 

 never rises from the femur as in some of the ITystricoinorplia. 

 In Oeorychus 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 Oerbillus, Mus barbarus, Mus rattus, and Myodes the tendon 

 does not divide at all, but goes entirely to the cuneiform. In 

 Heterofiiys the division is well marked, but both parts are inserted 

 into the cunfeiform. ■ ■ - 



' P.Z.S. 1887, p.68. ■ 



