352 THE MUSCLES. 



and the superficial gluteus, and extends from the sacral spine to the leg, describ- 

 ing a curv«, the convexity of which is posterior. 



jTorm — Structure. — It is elongated from above to below, bifid at its superior 

 extremity, thick and prismatic, but nevertheless flattened on both sides. Its 

 muscular fibres are of a pale-red colour, are parallel to each other, and follow 

 the general direction of the muscle ; they terminate, inferiorly, on an aponeurosis, 

 by a flat tendon. In its middle portion, the body shows traces of the inter- 

 section which has obtained for this muscle the name — semitendinosus, in Man. 



Attachments. — This muscle arises, above, by one of its branches, from the 

 sacral spine and the sacro-sciatic hgament, in common with the posterior portion 

 of the superficial gluteus, with which it exchanges some fibres ; ^ by the other 

 branch, which is the shortest, from the ischial tuberosity. Its inferior aponeu- 

 rosis is confounded with that of the tibia ; the tendon glides over the internal 

 surface of the tibia, and is inserted into its anterior crest. 



Belations. — Its sacro-sciatic branch is covered by the gluteal aponeurosis, and 

 covers the superficial gluteus. For the remainder of its extent, it is related : 

 posteriorly, to that aponeurosis ; anteriorly, to the sciatic nerves ; externally, to 

 the superficial gluteus and gastrocnemius ; internally, to the semimembranosus 

 and the great adductor of the thigh. 



Action. — It is a flexor of the leg, and tensor of the tibial aponeurosis, when 

 its fixed point is above ; when the leg is fixed, it becomes one of the active 

 agents in rearing. 



3. Semimembranosus (Adductor Magnus) (Figs. 193, 6 ; 194, 10 ; 195, 13). 



Synonyms. — Ischio-tibialis internua — Girard. (Great iscMo-femoralis—Leyh). 



Situation — Volume — Extent — Direction. — Situated within the semitendinosus, 

 and shorter and thinner than it, the semimembranosus extends from the ischium 

 to the inferior extremity of the femur, and follows an oblique direction down- 

 wards and forwards. 



Eorm — Structure. — Elongated vertically, flattened on each side, prismatic, thick 

 at its anterior, and very thin at its posterior borders. It is also voluminous at 

 its upper extremity, which has a small prolongation, the point of which ascends 

 to the base of the tail ; it is contracted, and terminated by a short tendon, at its 

 inferior extremity. It is formed of thick muscular fasciculi, which all terminate, 

 below, on the terminal tendon. 



Attachments. — Above : 1. To the aponeurosis of the coccygeal muscles, by the 

 thin prolongation from its superior extremity. 2. To the ischial tuberosity, and 

 the inferior face of the ischium. Below, to the small eminence situated within 

 the internal condyle of the femur. 



Belations.— lnwa,Tds, with a very thin prolongation from the gluteal aponeu- 

 rosis, and with the ischo-cavernous muscle and short adductor of the leg ; out- 

 wards, with the semitendinosus, the biceps femoris, and the sciatic nerves ; in 

 front, with the great adductor of the thigh, which is so intimately united to it 

 that some difficulty is experienced in separating their fibres. 



Action. — It is an adductor of the limb and an extensor of the thigh, when 

 its fixed point is above ; but when the femur is fixed, it is an auxiliary in 

 rearing. 



* The portion of this muscle whicli is attached to the sacral spine, certainly represents the 

 meet inferior part of the superficial gluteus of Man. 



