166 ANATOMY OF THE WOOD RAT 



or 14 per cent of the length of the tibia, is usually described as 

 pear-shaped (although like half a pear would be more ap- 

 propriate), and fits against the trochlea of the femur. It is 

 imbedded in the capsule of the joint, and the patella liga- 

 ment passes from its distal end to the tibia. 



Upon the cranio-proximal part of the patella is inserted 

 the rectus femoris, and on the latero-distal part, the biceps 

 femoris anticus. Upon the tendinous tissue cranio-proximad 

 and mediad to the patella are inserted the gluteus superficialis 

 anterior, vasti lateralis, medialis, and femoris, and the 

 adductor magnus. 



Tibia. The tibia is the longer of the two bones of the 

 lower leg, and is seldom shorter than the femur. In Homo- 

 dontomys it measures from 44.7 to 45.2 per cent of the func- 

 tional length of the hind leg; in Neotoma, from 44.3 to 44.8 

 per cent; and in Teonoma a trifle less — about 43 per cent. 

 It is relatively lightest in Neotoma, and considerably the 

 most robust in Teonoma. 



The proximal head of the tibia is divided into a lateral 

 and a medial tuberosity, with a slight depression between. 

 Distad to the head, upon the cranial border, is the tubercle. 

 This has its own center of ossification, and the distal margin 

 is often separated from the shaft in the case of a well- 

 cleaned skeleton. The lateral tuberosity has a caudal pro- 

 jection with an articular surface for the attachment of the 

 fibula. 



The cranio-medial border of the shaft is largely devoid 

 of muscle. Upon the extreme cranio-medial portion ad- 

 joining the head is inserted the semimembranosus anticus. 

 This point is marked by a roughness which stands in relief 

 from the remainder of the shaft — not a true process, as it 

 conforms to the shape of the head, but one to all intents. It 

 is considerably best defined in Teonoma, although in that 

 animal the attached muscle appears no larger. Distad of the 

 above prominence is situated the popliteal fossa, over which 



