704 MAMMALIAN ANATOMY 



posterior surface. In the border is inserted part of the tendon of the 

 quadriceps extensor muscle. 



The external and internal borders are rounded, and afford attach- 

 ment to the external and internal parts of the quadriceps muscle. 



The anterior surface is gently convex, vertically striated, and 

 marked by venous foramina ; it is covered with an expansion of the 

 quadriceps tendon, and separated from the skin only by a sac filled 

 with fluid, a so-called bursa. At the apex is fastened the ligameiitum 

 patellae. 



The posterior surface (Fig. -540) is mainly occupied by a large, 

 transversely oval articular surface, covered in the recent state with 



a layer of articular cartilage. Below this sur- 

 FIG. 540. 



face is a triangular roughened area for the 

 attachment of the ligamentum patellae. The 

 articular surface is divided by a line of maxi- 

 mum convexity into two facets, whereof the ex- 

 ternal is larger and more deeply concave, and 

 EIGHT PATELLA, posTE- Hides on the external condyle of the femur, and 



RIOR VIEW. J 



i, 2, articular facet for the the internal is smaller, flatter, and glides on the 



trochlea of the femur ; 3, apex . -, - -, T-> j i r 



of the bone roughened for the internal COnclyle. jBOtll facets are CrOSSed trans- 

 attachment of its ligament. -, c> c ,1 -i i T 



versely not far from the upper and lower borders 



by two faint lines, and the internal facet exhibits, in addition, along 

 the internal border a narrow, more concave area. In this way the 

 articular surface may be said to present seven facets, which, in the 

 different motions of the knee-joint, are applied to the condyles as 

 follows : the two narrow upper facets touch the condyles only in ex- 

 treme flexion of the leg on the thigh, the larger middle facets in 

 partial flexion, and the smaller lower facets in extension, when the leg 

 is perfectly straight ; the vertical internal seventh facet glides on the 

 internal condyle in all positions of the leg. 



ADDITIONAL SESAMOID BONES. 



Three other sesamoid bones stand in relation to the back of the 

 knee-joint. 



Two of these are found in the tendons of the gastrocuemius muscle, 

 one on each side close to its origin on the supracondyloid ridge just 

 above the .condyle. These sesamoids are about the size of the unciform 

 of the wrist, but have the form of an irregular cone so placed that the 



