243 



A MANUAL OF ANATOMY 



portion of the vastus internus. The apex is blunt, and, together with 

 the adjacent marginal parts, gives attachment to the ligamentum 

 patellae, by which the bone is connected with the tubercle of the tibia. 



The anterior surface, which is slightly convex, is vertically 

 striated and covered by a prolongation of the tendon of the quadri- 

 ceps extensor cruris. It is perforated by numerous nutrient fora- 

 mina, and is subcutaneous, being separated from the integument 

 by the prepatellar bursa. 



The posterior surface is divided into two parts — articular and 

 non-articular. The non- articular part represents the lower fourth, 

 and is rough and depressed. It lodges a collection of fat covered 

 by synovial membrane. The articular part corresponds with the 

 upper three-fourths, and is divided into two unequal parts by a round 

 vertical ridge, which is received into the groove of the patellar 

 surface of the femur. The external division is broad and concave 

 from side to side, whilst the internal is narrow and convex in 

 the transverse direction. Excluding a narrow vertical zone at the 

 inner part of the inner division, each division is subdivided by 

 two slight transverse ridges into three horizontal zones — upper, 

 middle, and lower, of which the middle is the largest and broadest. 

 These six horizontal facets articulate with the patellar surface of the 

 femur, the lower facets being in contact with the upper part of the 

 patellar surface in extension of the knee-joint, the middle patellar 

 facets with the middle portion of the patellar surface of the femur in 

 semiflexion, and the upper patellar facets with the lower parts of 

 the patellar surface of the femur in flexion of the knee-joint. The 

 vertical zone at the inner part of the inner division of the articular 

 surface (close to the inner border of the bone) constitutes a seventh 

 facet, which may be called the miner's facet. In extreme flexion 

 of the knee-joint this facet articulates with the semilunar facet 

 (miner's facet) on the outer part of the tibial surface of the internal 

 condyle of the femur close to the intercondylar fossa, whilst the 

 upper and outer horizontal facet is in contact with the front part 

 of the external condyle. 



The patella receives its arteries from the superficial branch of 

 the anastomotica magna of the femoral, inferior articular branches 

 of the popliteal, and anterior tibial recurrent. 



Structure. — The patella, being a short bone, is composed princi- 

 pally of dense cancellated tissue with close meshes, surrounded 

 by compact bone, which is much thicker in front than behind. 



Ossification. — The original cartilage is deposited in the tendon of the quad- 

 riceps extensor cruris in the third month of intra-uterine life. In this cartilage^ 

 a single centre appears in the third year, and ossification is completed about : 

 the age of puberty. 



The Tibia. 



The tibia, or shin-bone, is the inner and larger of the two 

 bones of the leg, and alone transmits the weight of the body to 

 the foot. The posterior surfaces of the shafts of the tibia andj 



