292 



THE SKELETON. 



FIG. 218. Right patella. An 

 terior surface. 



FIG. 219. Right patella. 

 Posterior surface. 



anterior part of the knee-joint. It is usually regarded as a sesamoid bone, 

 developed in the tendon of the Quadriceps extensor. It resembles these bones 



(1) in its being developed in a 

 tendon ; (2) in its centre of ossi- 

 fication presenting a knotty or 

 tuberculated outline similar to 

 other sesamoid bones ; (3) in its 

 structure being composed mainly 

 of dense cancellous tissue, as in 

 the other sesamoid bones. It 

 serves to protect the front of 

 the joint, and increases the 

 leverage of the Quadriceps ex- 

 tensor by making it act at a 

 greater angle. It presents an 

 anterior and posterior surface, three borders, and an apex. 



The anterior surface is convex, perforated by small apertures, for the passage 

 of nutrient vessels, and marked by numerous rough, longitudinal striae. This 

 surface is covered, in the recent state, by an expansion from the tendon of the 

 Quadriceps extensor, which is continuous below Avith the superficial fibres of the 

 ligamentum patellae. Jt is separated from the integument by a bursa. The 

 posterior surface presents a smooth, oval-shaped, articular surface, covered with 

 cartilage in the recent state, and divided into two facets by a vertical ridge, which 

 descends from the superior border toward the inferior angle of the bone. The 

 ridge corresponds to the groove on the trochlear surface of the femur, and the two 

 facets to the articular surfaces of the two condyles ; the outer facet, for articulation 

 with the outer condyle, being the broader and deeper. This character serves to 

 indicate the side to which the bone belongs. Below the articular surface is a 

 rough, convex, non-articular depression, the lower half of which gives attachment 

 to the ligamentum patellae, the upper half being separated from the head of the 

 tibia by adipose tissue, in which may be found a bursa. 



The superior border is thick, and sloped from behind, downward and forward : 

 it gives attachment to that portion of the Quadriceps extensor which is derived 

 from the Rectus and Crureus muscles. The lateral borders are thinner, converging 

 below. They give attachment to that portion of the Quadriceps extensor derived 

 from the external and internal Vasti muscles. 



The apex is pointed, and gives attachment to the ligamentum patellae. 

 Structure. It consists of a nearly uniform dense cancellous tissue covered 

 by a thin compact lamina. The cancelli immediately beneath the anterior surface 

 are arranged parallel with it. In the rest of the bone they radiate from the 

 posterior articular surface toward the other parts of the bone. 



Development. By a single centre, which makes its appearance, according to 

 Beclard, about the third year. In two instances I have seen this bone cartilagi- 

 nous throughout, at a much later period (six years). More rarely, the bone is 

 developed by two centres, placed side by side. Ossification is completed about the 

 age of puberty. 



Articulations. With the two condyles of the femur. 



Attachment of Muscles. To four : the Rectus, Crureus, Vastus internus, and 

 Vastus externus. These muscles, joined at their insertion, constitute the Quadriceps 

 extensor cruris. 



Surface Form. The external surface of the patella can be seen and felt in front of the 

 knee. In the extended position of the limb the internal border is a little more prominent than 

 the outer, and if the Quadriceps extensor is relaxed, the bone can be moved from side to side 

 and appears to be loosely fixed. If the joint is flexed, the patella recedes into the hollow 

 between the condyles of the femur and the upper end of the tibia, and becomes firmly fixed 

 against the femur. 



Surgical Anatomy. The main surgical interest about the patella is in connection with 

 fractures ; which are of common occurrence. They may be produced by muscular action ; that 



