TRICEPS EXTENSOR OF KNEE. 571 



nerves : the part external to the vessels is the vastus externus, and the 

 larger mass, internal to them, is the vastus internus. 



To make out the lower separation of the two, look to the outer aspect 

 of the thigh about half way down, where the long and vertical fibres of 

 the vastus externus descending to their tendon, cross over others (deeper), 

 which are continued obliquely inwards, and belong to the inner vastus. 



The VASTUS EXTERNUS has a very narrow attachment to the femur in 

 comparison with its size. It takes origin along the upper half of the 

 femur, by a piece from half an inch to an inch thick, which is attached 

 to the root of the neck of the femur, and the fore and outer parts of the 

 root of the great trochanter ; to the line connecting the trochanter with the 

 linea aspera ; and to the upper half of the linea aspera, and the contiguous 

 external intermuscular septum. Interiorly the fibres of the muscle end in 

 an aponeurosis which blends with the tendons of the rectus and vastus 

 internus in the common tendon, and sends a slip to the outer edge of the 

 patella. 



The muscle is pointed at the upper end ; but enlarged below where it 

 produces the prominence on the outer side of the thigh. Its cutaneous 

 surface is aponeurotic above, and is covered by the rectus, tensor vaginae 

 femoris, and gluteus muscles. The deep surface rests on the vastus inter- 

 nus, and receives branches of the external circumflex artery and anterior 

 crural nerve. 



The VASTUS INTERXUS (fig. 196, K ) form the large head of the exten- 

 sor. 1 The fleshy mass arises from the anterior and two lateral surfaces of 

 the shaft of the femur, except where the vastus externus is attached, and 

 its limits may be thus indicated : Upwards it reaches as far as the ante- 

 rior introchanteric line ; downwards, in the middle, to about two inches 

 from the articular end of the femur ; and laterally to both intermuscular 

 septa. At the lower end of the muscle the fibres terminate in an aponeu- 

 rosis, which blends in the common tendon of insertion, and is attached to 

 the patella lower than the vastus externus. 



The upper part of the muscular mass is buried beneath the sartorius 

 and rectus muscles ; but the lower part is superficial, arid projects more 

 than the vastus externus ; some of the lowest fibres are almost transverse, 

 and will be able to draw inwards the patella. The adductor muscles are 

 almost inseparably joined with this vastus along the attachment to the 

 linea aspera. 



Dissection. The tendon of the extensor will appear by dividing along 

 the middle line of the patella and knee-joint a thin aponeurotic layer, 

 which is derived from the lower fleshy fibres of the muscle, and covers the 

 joint. On reflecting inwards and outwards that fibrous layer the tendon 

 will be laid bare to its insertion into the tibia. 



The tendon of the extensor muscles of the leg is common to the rectus, 

 the vastus externus, and vastus internus. It is placed in front of the 

 knee-joint, to which it serves the office of an anterior ligament. Wide 

 above where the muscular fibres terminate, it narrows as it descends over 

 the joint, and is inserted inferiorly into the prominence of the tubercle of 

 the tibia, and into the bone below it for an inch ; close to its attachment 

 to the tibia a synovial bursa is beneath it. In it the patella is situate, 



1 Sometimes the part of the mass, inside a line continued upwards from the 

 inner border of the patella, is named crureus : naturally there is not any separa- 

 tion at that spot. 



