78 ELEMENTS OF MAMMALIAN ANATOMY 



The patella, or knee-cap (Fig. 22), is a sesamoid bone de- 

 veloped in the tendon of the quadriceps extensor muscle (Fig. 

 58). It is somewhat the shape of an almond and about half 

 its size. It articulates with the trochlea of the femur. 



The tibia is the larger bone of the crus. It presents two 

 enlarged extremities and a shaft whose cross-section is tri- 

 angular. It articulates with the femur and fibula proximally 

 and the fibula and talus distally (Fig. 22). This is the longest 

 bone in the cat's skeleton. Between the concave condyles on 

 the proximal end is a notch giving attachment to the crucial 

 ligament of the knee-joint (Figs. 42, 47). 



The prominences of the lateral and medial aspects of the 

 proximal extremity are the external and internal tuberosities 

 respectively. Beneath the former is the facet for articulation 

 with the fibula (Fig. 42). The tubercle, a prominence on the 

 cranial side of this extremity, is for the insertion of the liga- 

 mentum patellcB, which is really the termination of the tendon of 

 the quadriceps extensor muscle (Fig. 58). On the caudal 

 aspect between the condyles is the popliteal notch. The sharp 

 cranial border of the bone forms the crest. On the distal 

 extremity is a process, the internal malleolus, bearing two 

 grooves, the more caudal of w^hich shelters the tendon of the 

 flexor longus digitorum muscles while the other is for the tibialis 

 posticus (Fig. 58). A facet is present on the lateral aspect of 

 this extremity for articulation with the fibula. 



The fibula in proportion to its length is the slenderest bone 

 in the skeleton. It is the outer or lateral bone of the crus, and 

 articulates proximately with the tibia and distally with the tibia 

 and talus (Fig. 22). The proximal extremity is the head, upon 

 which is a circular facet for articulation w^ith the tibia. The 

 sharp edge along the cranial aspect of the shaft furnishes 

 attachment to the interosseous membrane uniting the two bones 

 of the crus. The medial aspect of the distal extremity shows 

 a prominent facet for articulation with the talus. Immedi- 

 ately proximal to this is the articular surface for the tibia. 



