J. Playfair McMurrich 59 



In the opossum tlic pronator tibite is a muscular sheet which extends 

 obliquely from the fibula to the tibia throughout the greater part of the 

 length of those bones. It takes its origin partly from the inner border 

 of the fibula, but mainly from the strong aponeurosis which separates 

 it from the tibialis posticus and the flexor digitorum tibialis above and 

 the flexor digitorum fibularis below. In its upper part the fibers are 

 directed very obliquely, indeed, almost directly tibia-wards, to the upper 

 part of the tibia, and in this upper portion the muscle is composed of 

 two fairly distinct sheets of fibers, one lying anterior to the other and 

 separated from it by a distinct layer of areolar tissue. Below (Fig. 

 7, PT) , however, there is no such separation of two layers, and the fibers 

 have a more vertical course. The partial separation above, already 

 noted by Young, 8i, is apparently of " prophetic " interest in fore- 



FiG. 12. — Transverse section through the cius of the Mouse just below the knee 

 joint. F, fibula ; Ge, gastrocnemius lateralis ; Oi, gastrocnemius medialis ; P^ and P^, 

 oblique and vertical portions of popliteus ; PI, plantaris ; T, tibia. 



shadowing the difi:erentiation of the muscle into an upper or popliteal 

 portion and a lower or pronator tibial portion. 



In the mouse the popliteus arises from a strong fibro-cartilaginous 

 band attached above to the outer condyle of the femur. Those fibers 

 which arise from the tibial side of the band (Fig. 12, P") have a much 

 more oblique direction than the rest (P-) and are inserted into the tibia 

 above them. iSTo distinct indications could be discovered of a repre- 

 sentative of the pronator tibiae, i. e., a lower portion of the muscle, 

 although it is possible that some scattered fibers which lie anterior to 

 the main mass of the flexor digitorum fibularis and have an oblique 

 direction, may represent it. A separation between these fibers and the 

 flexor was, however, at best indistinct. 



In the cat the popliteus takes its origin from a sesamoid bone which 

 is attached by a strong tendon to the outer condyle of the femur. The 



