MUSCLES OF LOWER LIMB 453 



which correspond with the musculature on the dorsal and ventral sides of the 

 (shark's fin. The dorsal musculature is supplied by nerve branches which arise 

 from the back of the lumbo-dorsal plexus ff em oral, gluteal, and peroneal nerves), 

 the ventral musculature by branches which arise from the front of the plexus 

 obturator and tibial nerves). Owing, however, to the rotation which the limb 

 makes during embryonic development, the musculature which primitively lies on 

 the dorsal side of the limb-bud comes to lie on the front and lateral side of the 

 extremity and the musculature of the ventral side of the limb-bud comes to lie 

 on the back and medial side of the extremitj^ or in the sole of the foot. The side 

 of the limb which primitively wae toward the head becomes the medial side 

 of the limb, and that which faced caudalward comes to lie laterally. While 

 this makes the primitive relations of the musculature of the limb at first somewhat 

 confusing, it is possible to approximate these primitive conditions by abducting 

 the limb and rotating it so that the sole of the foot faces forward. An under- 

 standing of the innervation of the limb is thus greatl}^ facilitated. 



In the region of the hip the musculature of the dorsal division is that which 

 arises from the spinal column and ilium and is inserted into the upper part of the 

 femur and into the fascia of the thigh. It includes the chief flexor of the thigh, 

 the ilio-psoas (fig. 406), and the most powerful extensor, the gluteus maximus 

 (fig. 413), as well as several important rotators and abductors, gluteus jnedius and 

 yninimus, 'piriformis and tensor fa scice latce (fig. 408). The ilio-psoas is innervated 

 by nerves from the back of the lumbar, the other muscles by nerves from the back 

 of the sacral plexus. The musculature of the ventral division arises from the 

 pubis and ischium, is inserted into the femur near the great trochanter and serves 

 to adduct the thigh and rotate it lateralward, obturator internus, gemelli, quadratus 

 femoris (fig. 408) and obturator externus (fig. 406). The obturator externus is 

 innervated by the obturator nerve from the front of the lumbar plexus, the other 

 muscles by special branches from the front of the sacral plexus. 



In the thigh there are three well-marked groups of muscles, an anterior or 

 extensor group (fig. 411), a medial or adductor group (fig. 411), and a posterior or 

 flexor group (fig. 408). The anterior group belongs to the primitive dorsal 

 division, the other two groups to the ventral division. 



The muscles of the anterior group (fig. 411) the sartorius and quadriceps arise 

 from the ilium and the shaft of the femur and are inserted into the tibia. The 

 quadriceps flexes the thigh and extends the leg. The sartorius flexes both the 

 thigh and the leg and rotates the former lateralward, the latter medialward. 

 They are innervated by the femoral nerve. The muscles of the medial group 

 (fig. 411), gracilis, pectineus, adductor brevis, longus, and magnus, arise from the 

 pubis and the inferior ramus of the ischium and are inserted into the shaft of the 

 femur. They adduct and flex the thigh. They are innervated by the obturator 

 nerve. The adductor magnus gets part of its nerve-supply from the sciatic. 

 The pectineus usually gets all or most of its supply from the femoral. The rea- 

 sons for including it in this group are given below. The posterior group (fig. 408) 

 consists of the semitendinosus and semimembranosus, which arise from the ischial 

 tuberosity, and of the biceps, one head of which also arises from the ischial tuber- 

 osity while the other arises from the shaft of the femur. The semimembranosus 

 and semitendinosus are inserted into the tibia, the biceps into the fibula. They 

 are innervated by branches of the sciatic. They extend the thigh and flex the 

 knee. The semitendinosus rotates the leg medialward, the biceps lateralward. 



In the leg there are also three groups of muscles, an anterior, a lateral and a 

 posterior. The two former belong to the dorsal division and are innervated by 

 the peroneal nerve. The last belongs to the ventral division and is innervated by 

 the tibial nerve. The muscles of the anterior group (fig. 415), the tibialis anterior, 

 extensor digitorum longus, peroneus tprtius and extensor hallucis longus, arise from 

 the tibia and fibula and are inserted into first and fifth metatarsals and into the 

 two distal rows of phalanges. They flex the ankle and extend the toes. The 

 extensor digitorum longus and peroneus tertius evert the foot. The muscles of 

 the lateral group (fig. 415), the peroneus longus and brevis, arise from the fibula, 

 send tendons behind the lateral malleolus and are inserted respectively into the 

 first and the fifth metatarsals. They extend and evert the foot. The posterior 

 group (figs, 413, 416) may be separated into two subdivisions, a superficial and a 

 deep. The superficial subdivision (fig. 413) consists of the gastrocnemius, which 



