THE KNEE 



1445 



or by early tuberculous ulceration of the contiguous cartilages. The numerous 

 longitudinal striae or sulci on the anterior surface of this bone can now also be 

 detected. In these are embedded tendinous bundles of the rectus, so as to give 

 firmer leverage. The fact that these fibres, thus tied down, are liable after stretch- 

 ing and tearing to fold in between the ends of the bone after fracture, is a ready 

 explanation of the difficulty of ensuring bony union here. (Macewen.) The 

 patella is separated from the tibia by a pad of fat and a deep bursa, save at its 

 insertion. Owing to the lowest part of the patella being thus separated from the 

 joint by fat, fracture here does not, necessarily, open the joint. 



The bone has the following relation to the femur in different positions : — (1) In extension, the 

 pateUa rises over the condyles, and in full extension only the lower third of its articular surface 

 rests upon that of the condyles; its upper two-thirds lies upon the bed of fat which covers the 



Fig. 1163. — Deep Dissection of the Gluteal Region. 



Hunterian Museum.) 



Gluteus medius 



\ 



(From a preparation in the 



Gluteus minimus 



Piriformis, divided 



into two by the 



sciatic nerve 



Great trochanter 



Obturator externus 

 Quadratus f emoris 



Fascial insertion of 

 gluteus mazimus 



Horizontal fibres of 

 adductor magnus 



Insertion of gluteus 

 maximus 



Sciatic foramen 

 - (notch) 



Gluteal nerve sup- 



plying portions of 



gluteus medius 



Gluteus maximus 



Obturator internus. 

 Below is the infe- 

 rior gemellus. The 

 superior gemellus 

 is absent 



Perineal branches of 

 posterior cutaneous 

 nerve 



Sciatic nerve. Under it, 

 oblique fibres of adduc- 

 tor magnus are seen 



Posterior femoral 

 cutaneous nerve 



lower and front part of the femur. (2) In extreme flexion, as the prominent anterior surface 

 of the condyles affords leverage to the quadriceps, the patella needs to project very Uttle; thus, 

 only its upper third is in contact with the femur, its lower two-thirds now resting on the pad of 

 fat between it and the tibia. (3) In semiflexion the middle third of the patella rests upon the 

 most prominent part of the condyles. (Humphry.) While the bone now affords the greatest 

 amount of leverage to the quadriceps, it is also submitted to the greatest amount of strain from 

 this muscle, which is acting almost at a right angle to the long axis of the patella. This position 

 may therefore be called the 'area of danger,' as, in a sudden and violent contraction, the patella 

 may be snapped across by muscular action, aided by the resistance given by the condyles, in 

 the same way as a stick is snapped across the knee. The amount of separation of the fragments 



