THE TIBIA, OR SHIN BONE 233 



In the male its direction is vertical and parallel with the bone of the opposite 

 side; but in the female it has a slightly oblique direction downward and outward, 

 to compensate for the oblique direction of the femur inward. It presents for 

 examination a shaft and two extremities. 



The Proximal or Upper Extremity. The upper extremity, or head, is 

 large, and expanded on each side into two lateral eminences, the internal and 

 external tuberosities (condylu* medial is and condylus lateralis). Superiorly, each 

 tuberosity presents a smooth, concave surface (Jades articularis superior), which 

 articulates with a condyle of the femur. The internal articular surface is oval in 

 shape and concave from side to side; the external one is circular, concave from side 

 to side, but slightly convex from before backward, especially at its posterior 

 part, where it is prolonged on to the posterior surface for a short distance; the 

 central portions of these surfaces articulate with the condyles, while the peripheral 

 portions are overlaid by the semilunar cartilages of the knee. Between the two 

 articular surfaces, and nearer the posterior than the anterior aspect of the bone, 

 is an eminence, the spine of the tibia (eminentia intercondyloidea); surmounted 

 by a prominent tubercle on each side (the tuberculum inter condyloideum mediale 

 and the tuberculum intercondyloideum laterale), on to the lateral aspect of which 



Posterior crucial 



External semilunar ^. ligament, 

 cartilage. ^ = *- 



Internal semilunar 

 rtilage. 



nternal semilunar 

 cartilage. 



External semilunar Anterior crucial 



cartilage. ligament. 



FIG. 187. Upper surface of right tibia, showing attachment of crucial ligaments and semilunar cartilages. 



the facets just described are prolonged; in front and behind the spinous process 

 is a rough depression (fossa intercondyloidea anterior and the fossa intercondy- 

 loidea posterior) for the attachment of the anterior and posterior crucial ligaments 

 and the semilunar fibrocartilages (Fig. 187). 



The anterior surfaces of the tuberosities are continuous with one another, form- 

 ing a single large surface, which is somewhat flattened; it is triangular, broad 

 above, and perforated by large vascular foramina; narrow below, where it ter- 

 minates in a prominent oblong elevation of large size, the tubercle of the tibia 

 (tuberositas tibiae); the lower half of this tubercle is rough, for the attachment of 

 the ligamentum patellae; the upper half presents a smooth facet supporting, in 

 the recent state, a bursa which separates the ligament from the bone. Poste- 

 riorly the tuberosities are separated from each other by a shallow depression, 

 the popliteal notch ( incisura poplitea), which gives attachment to part of the pos- 

 terior crucial ligament and part of the posterior ligament of the knee-joint. The 

 inner tuberosity presents posteriorly a deep transverse groove, for the insertion 

 of one of the fasciculi of the tendon of the Semimembranosus. Its lateral surface 

 is convex, rough, and prominent, and gives attachment to the internal lateral 

 ligament. The outer tuberosity presents posteriorly a flat articular facet (fades 

 articularis fibularis), nearly circular in form, directed downward, backward, 



