THE BONES. 91 



105. 3. Patella s. Rotula, Knee-pan. 



Position : between femur and tibia, before the knee. The 

 largest os sesamoideum. 



Figure : flat, roundish, triangular, however very variable ; above 

 broad, below pointed. 



Connection : with the femur and tibia. 



a. Anterior surface, convex, covered by a thick fibrous tissue, beneath the 

 skin. 



b. Posterior surface, fits close upon the Trochlea of the inferior extremity 01 

 the femur; is covered with cartilage, and presents : 



1. Crista, from above, downwards and inwards. 



2. Fossa articular, externa, broad, and internet, narrow. 



c. Circumference. Superior border, basis, thick, for the tendons of the 

 extensors of the leg. Lateral borders, for lig. capsulare. Point, apex, lies 

 towards the Spina tibia [for ligam. Patella]. 



In flexion of the leg upon the thigh the Patella remains fixed and pro- 

 jects, in extension it is moveable and serves as a roller for the Extensor 

 muscles. 



Structure. Entirely spongy, only covered upon the anterior surface with a 

 thin layer of compact tissue which, as an exception in these short bones, con- 

 sists of longitudinal fibres. 



Development. From one osseous centre in the third year. 



III. Ossa pedis, Bones of the feet. 



106. 1. Tarsus, root of the foot, instep, 



consists of seven bones, placed unequally in two rows; arched 

 above, hollow below. 



a. Posterior row, consists of the two largest bones of the 

 Tarsus. 



1. Astragalus s. Talus, knuckle bone. Situation and connection: below the 

 Tibia, above the Colds, internal to Malleolus exter nits, fibula, behind the navicular 

 bone. Figure irregularly cubical. Six surfaces. Body and head. 



a. Body. Superior surface, a half trochlea for the tibia; Lateral surfaces 

 flat enclosed by the malleoli. Inferior surface, for calcaneus, concave. Poste- 

 rior surface with a groove, for flex, halluc. long. 



b. Head, for os naviculare, united to the body by the Collum astrag., has 

 above, a broad notch, before, an articular surface, for os naviculare, below, a fossa 

 which forms with another on the Proc. anterior Calcanei, the Sinus tarsi; lies 

 on the anterior surface of the astragalus. 



2. Calcaneus, heel bone, the largest of the tarsal bones. Position : below 

 the Astragalus, behind the Cuboid. Figure: longitudinal; a body and pro- 



a. Body. Posterior termination, proc. poster, s. calx, heel, for the tendo* 

 Achillis; inferior, narrow surface, with two tubercles; superior surface, with 

 two convex articular surfaces, for the Astragalus ; external surface, only covered 



