THE MUSCLES OF THE HIND-LIMB 59 



limbs have taken on some part of the bodily support, the 

 condition is as yet unchanged, so far as the fibular origin 

 of the M. pronator tibiae is concerned, and this muscle is 

 found as (but perhaps only as part of) the M. popliteus 

 of the higher Vertebrates. The superficial ^portion pos- 

 sesses practically no power of rotation, and the move- 

 ment between the two bones is becoming somewhat more 

 limited. Among the Mammals, the Monotremes and 

 some of the less specialized Marsupials still possess the 

 M. popliteus, which is the exact homologue of the deep, 

 or ulnar, part of the M. pronator radii teres, for it arises 

 from the upper end of the fibula, and is inserted into the 

 tibia, upon which bone it produces some degree of rota- 

 tion. Among some of the Insectivora, the M. popliteus is 

 in a half-way stage, for it arises from the upper end of 

 the fibula and from the capsule of the knee-joint. This 

 is the case in some of the Shrews, and apparently also in 

 Chrysochloris, the Golden Moles (Dobson). In the common 

 Hedgehog (Erinaceus), the muscle has migrated still 

 farther towards the femur, but it still arises from the 

 capsule of the joint as well as from the femoral condyle. 

 In some of the Lemurs, the M. popliteus still retains 

 connection with the fibula through the intervention of a 

 tendon and a sesamoid bone, just as it does in some 

 Lizards; but in all other Primates the main origin is 

 entirely from the femur, with occasional slight excursions 

 to the ligaments of the joint. A small, deeper portion, the 

 M. peroneo-tibialis, however, retains connection with the 

 fibula, but this muscular slip is derived, in all probability, 

 from the deeper interosseous muscle of the lower Verte- 

 brates. In Man the popliteus muscle arises entirely 

 from the femur, and even the peroneo-tibialis is only 

 present in one out of some seven subjects, according to 

 Gruber (see Fig. 21). The story of this muscle group 

 appears to be fairly clear from the functional point of 

 view. So long as the old mobility was retained, the 

 rotator muscle passed from bone to bone across the second 



