ANTERIOR MUSCLES OF THE LEG. 279 



The ilio-psoas muscle, the flexor of the hip-joint, flexes the thigh on the body, or 

 the body on the thigh, according as either of these is the most fixed. 



The pectineus is partly a flexor and partly an adductor. 



The adductores magnus, longus, and brevis adduct the thigh, and, along with their 

 opponents the gluteus medius and minimus, and with the gluteus maximus, balance 

 the body on the femur in walking. 



The adductor muscles and the ilio-psoas t together with t.he pectineus, being all in- 

 serted at the back part of the femur, tend to rotate the thigh outwards at the same time 

 that they produce their adducting and flexing actions. The advantage of this prepon- 

 derance of rotators outwards over rotators inwards becomes apparent by reference to 

 the movements which take place in walking. When a step is taken, the pelvis is 

 drawn forwards on that side on which the foot has been advanced, which involves 

 a considerable rotation of the pelvis outwards at the other hip-joint, by the action of 

 the muscles of the opposite limb. 



The quadriceps extensor femoris extends the knee-joint ; but, as already mentioned 

 with regard to the gluteus maximus, its action is not requisite for the maintenance of 

 the erect attitude, the knee-joint remaining in complete extension without muscular 

 aid while the foot is firmly planted on the ground. This may be tested by the fact 

 that the patella of a person standing with the knee extended will be found to lie 

 quite loosely, but will become at once fixed when it is attempted to lift the foot. 



The rectus femoris, sartorius, gracilis, semitendinosus, semimembranosus, and 

 long head of the biceps act on both the hip and knee-joints. 



The sartorius produces the flexion of the hip and knee-joints, accompanied by 

 abduction, which occurs in the posture assumed by the tailor in sitting, and the 

 muscle derives its name from this circumstance. 



The rectus femoris flexes the hip and extends the knee ; it acts wholly from its 

 anterior head of origin when the thigh is fully extended, and the posterior head is 

 alone tense when the thigh is bent. 



The hamstring muscles extend the hip and flex the knee. It is to be observed, 

 however, that in the ordinary movements of the body, the hip and knee-joints are 

 flexed and extended together, and that therefore the joint on which those long muscles 

 act must be determined by the other muscles which pass over either of those joints 

 separately. 



The gracilis acts as an adductor on the hip-joint. The gracilis, semitendinosus, 

 and sartorius muscles form the group of rotators inwards at the knee-joint ; they act 

 along with the popliteus in this respect to greatest advantage in the flexed state of 

 the knee ; but they likewise favour the commencement of flexion by undoing that 

 rotation inwards of the femoral condyles on the tibia by which extension of the knee 

 is completed. 



The short head of the biceps is the only flexor of the knee, which passes over that 

 joint alone. The whole of thia muscle produces external rotation of the leg. 



The sulicrureus in extension of the knee-joint probably raises the upper part of the 

 synovial membrane, and prevents it from being pressed between the patella and 

 femur. 



MUSCLES OF THE LEG AND FOOT. 



ANTERIOR REGION. 



Between the tibia and fibula, on the front of the leg, are placed four 

 muscles the tibialis anticus, extensor proprius pollicis, extensor longus 

 digitorum, and peroneus tertius ; and on the dorsum of the foot one muscle 

 only arises, the extensor brevis digitorum. 



The tibialis anticus arises from the external tuberosity of the tibia, and 

 about two-thirds of the outer surface of that bone ; from a small portion of 

 the adjoining interosseous ligament ; from the strong fascia of the leg ; and 

 from an aponeurotic septum placed between it and the extensor longus 

 digitorum. The tendon in which all the muscular fibres terminate before 



