THE TIBIA 185 



or more bursse. The posterior surface is largely articular, covered with cartilage 

 in the recent state, and divided by a slightly marked vertical ridge, corresponding 

 to the groove on the trochlear surface of the femur, into a lateral larger portion 

 for the lateral condyle, and a medial smaller portion for the medial condjde. 

 Close to the medial edge a faint vertical ridge sometimes marks off a narrow articu- 

 lar facet, for the lateral margin of the medial condyle of the femur in extreme 

 flexion of the leg. Below the articular surface is a rough, non-articular depression, 

 giving attachment to the ligamentum patellae, and separated by a mass of fat from 

 the head of the tibia. 



The base or superior border is broad, sloped from behind downward and for- 

 ward, and affords attachment, except near the posterior margin, to the common 



Fig. 223. — The Superior Border or Base of the Left Patella. 

 Anterior surface 



Area for insertion of the quadriceps 

 extensor muscle 



Area in relation with synovial mem- 

 brane of knee-joint 



tendon of the quadriceps. The borders, thinner than the base, converge to the 

 apex below, and receive parts of the two vasti muscles. The apex forms a blunt 

 point directed downward, and gives attachment to the ligamentum patellae, by 

 which the patella is attached to the tibia. 



Structurally the patella consists of dense cancellous tissue covered by a thin compact layer, 

 and it receives nutrient vessels from the articular branch of the suprema genu (anastomotic), 

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



Ossification. — The cartilaginous deposit in the tendon of the quadriceps muscle takes place 

 in the fourth month of intra-uterine life. Ossification begins from a single centre during the 

 third year, and is completed about the age of puberty. 



THE TIBIA 



The tibia (figs. 224, 225) or shin-bone is situated at the front and medial side 

 of the leg and nearly parallel with the fibula. Excepting the femur, it is the 

 largest bone in the skeleton, and alone transmits the weight of the trunk to the 

 foot. It articulates above with the femur, below with the tarsus, and laterally 

 with the fibula. It is divisible into two extremities and a shaft. 



The upper extremity (or head) consists of two lateral eminences, or condyles. 

 Their superior articular surfaces receive the condyles of the femur, the articular 

 parts being separated by a non-articular interval, to which ligaments are attached. 

 The medial articular surface is oval in shape and concave for the medial condyle 

 of the femur. The lateral articular surface is smaller, somewhat circular in shape, 

 and presents an almost plane surface for the lateral condyle. The peripheral 

 portion of each articular surface is overlaid by a fibro-cartilaginous meniscus of 

 semilunar shape, connected with the margins of the condyles by bands of fibrous 

 tissue termed coronary ligaments. Each semilunar meniscus is attached firmly 

 to the rough interval separating the articular surfaces. This interval is broad 

 and depressed in front, the anterior intercondyloid fossa, where it affords attach- 

 ment to the anterior extremities of the medial and lateral menisci and the anterior 

 crucial ligament; elevated in the middle to form the intercondyloid eminence or 

 spine of the tibia, a prominent eminence, presenting at its summit two compressed 

 intercondyloid tubercles, on to which the condylar articular surfaces are prolonged; 

 the posterior aspect of the base of the eminence affords attachment to the posterior 

 extremities of the lateral and medial semilunar menisci, and limits a deep notch, 

 inclined toward the medial condyle, known as the posterior intercondyloid fossa 

 or popliteal notch. It separates the condyles on the posterior aspect of the head 

 and gives attachment to the posterior crucial ligament, and part of the posterior 

 ligament of the knee-joint. Anteriorly, the two condyles are confluent, and form 

 a somewhat flattened surface of triangular outline, the apex of which forms the 

 tuberosity of the tibia. The tuberosity is divisible into two parts. The upper 



