THE SKELETON. 



present in Halitherium, a fossil form. The hind-limbs are 



wanting among the Cetacea, but in a few forms nodules 



of bone or cartilage may represent the 



femur. In most Perissodactyla and Ro- 



dentia, and in some Insectivora and a 



few fossil Carnivora, a third trochanter 



is present. 



The patella, or knee-cap (Fig. 21), is 

 a sesamoid bone developed in the tendon 

 of the quadriceps extensor muscle (Fig. 

 52). It is somewhat the shape of an al- 

 mond and about half its size. It articu- 

 lates 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 triangular. 

 It articulates with the femur and fibula 

 proximally and the fibula and astragalus 

 distally (Fig. 21). 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. 41, 46). 



The prominences of the lateral and 

 mesal aspects of the proximal extremity 

 are the external and internal tuberosities 

 respectively. Beneath the former is the 

 facet for articulation with the fibula (Fig. 

 41). The tubercle, a prominence on the 

 cephalic side of this extremity, is for 

 the insertion of the ligamentum patellcz, 

 which is really the termination of the 

 tendon of the quadriceps extensor muscle (Fig. 52). On 

 the caudal aspect between the condyles is the popliteal 



ar 



FIG. 42. INNER OR 

 MESAL ASPECT 

 OF RIGHT FIB- 

 ULA. 



Facet for tibia; 

 ar, facet for as- 

 tragalus; ex, ex- 

 ternal malleolus; 

 h, head ; s, shaft ; 

 /, articular sur- 

 face for tibia ; gr, 

 groove for pero- 

 neus longus mus- 

 cle. 



a 



