THE TIBIA 153 



surface is subcutaneous; a bursa intervenes between it and the skin. The posterior 

 surface is concave, and in great part cartilage-covered, forming a compound articu- 

 lar surface for gliding upon the femoral condyles. A slightly marked vertical 

 ridge divides this surface into an outer larger portion for the external condyle, and 

 an inner portion for the internal condyle. A slender articular facet close to the 

 inner edge is sometimes marked off by a faint vertical ridge; this facet comes 

 in contact with the internal condyle in extreme flexion of the leg. The lower 

 part of the bone is terminated by a blunt point, which is embedded in the patellar 

 ligament, especially on the posterior aspect. The upper two-thirds of the circum- 

 ference receives directly the fibres of the vastus internus and externus, the crureus 

 and rectus femoris muscles. 



Blood-supply. — The patella receives tAvigs from the superficial In-anch of the 

 anastomotica, anterior tibial recurrent, and the inferior articular of the popliteal. 



Ossification. — Tlie cartilage for the patella appears in the fourth month of 

 intra-uterine life. The ossitic nucleus is visible in the third year. 



TRU TIBIA 



The tibia is the larger bone of the leg; it is situated on the inner side of, and 

 nearly parallel Avith, the fibula. The upper extremity, or head, consists of two 

 lateral eminences, or tuberosities. The superior surfaces of the tuberosities receive 

 the condyles of the fenuu', the articular surfaces being separated by a non-articular 

 ridge, to Avhich ligaments are attached. The internal articular surface is oval 

 in shape and concave for the internal condyle of the femur. The external 

 articular surface is smaller, somcAvhat circular in shape, and presents an almost 

 plane surface for the external condyle. The peripheral portion of each articular 

 surface is overlaid by a fibro- cartilage of semilunar shape, connected with the 

 margins of the tuberosities by bands of fibrous tissue termed coronary ligaments. 

 Each semilunar fibro-cartilage is attached firmly to the rough tract separating the 

 articular surfaces. This intermediate space is broad and depressed in front, where 

 it affords attachment to the anterior limlj of the internal and external semilunar 

 cartilages and the anterior crucial ligament. Projecting upAvards from the middle of 

 this surface is the spine of the tibia. The posterior aspect of the base of the spine 

 affords attachment to the posterior limb of the external and internal semilunar 

 fibro-cartilages, and limits a deep notch inclined toAvards the inner tuberosity; this 

 notch gives origin to the jiosterior crucial ligament. Anteriorly, the tAvo tuberosities 

 are confluent, and form a somcAvhat flattened surface of triangular outline; its apex 

 forms the tubercle of the tibia. The ligamentum patellte is inserted into the 

 loAver part of the tuljercle; the upper part is smooth and separated from the liga- 

 ment l)v a bursa. Laterally, the inner tuberosity is less prominent though more 

 extensive than the outer; near the posterior part of its circumference there is a deep 

 horizontal groove for the central portion of the semimembranosus tendon. The 

 margins of this groove and the surface of bone beloAV give attachment to the internal 

 lateral ligament of the knee. At a corresponding point of the outer tuberosity there 

 is a rounded articular facet for the head of the fibula; the circumference of the 

 facet is rough for ligaments. Above and in front of it is a ridge for the ilio-tibial 

 band. 



The shaft is prismatic, and A'ery thick near the head; towards the loAver third it 

 is thinner and tapering, and gradually expands toAvards the loAver end. It has three 

 borders : the anterior is very prominent, and known as the crest of the tibia : 

 commencing on the outer edge of the tubercle, it runs downwards and curves 

 iuAvards, to terminate at the anterior margin of the malleolus. This border gives 

 attachment to the deep fascia of the leg. The internal border starts from the 

 back of the internal tuberosity, and ends at the posterior margin of the malleolus. 



