286 THE MUSCLES. 



Action. It appears to raise (or render tense) the capsular ligament 

 during flexion of the femur. 



JB. Posterior Crural Region. 



This region is constituted by three muscles situated behind the thigh. 

 These are the long vastus, the semitendinosus, and the semimembranosus. 



Preparation. Place the subject in the first position, allow one hind leg to lie 

 unfastened, and incline the body to the corresponding side, leaving the other limb 

 attached to the supporting bar, with the thigh slightly flexed to make these muscles 

 tense. These preliminary arrangements being adopted, proceed in the f&llowing 

 manner : 1 . Make a transverse incision through the short adductor of the thigh, and 

 turn back the two portions to the right and left, so as to expose the whole of the 

 semimembranosus, which is to be afterwards dissected from the semitendinosus and the 

 great adductor of the thigh. 2. After removing the aponeurosis covering the long vastus 

 and semitendinosus, the latter is to be dissected by circumscribing as carefully as 

 possible its two superior insertions. 3. The long vastus is then to be prepared by 

 isolating the two component portions, whose sacro-sciatic insertion is revealed by 

 dividing the analogous insertion of the semitendinosus ; after which, reflect the entire 

 muscle in order to study its deep face, its femoral insertion, and its relations with the 

 subjacent organs. 



1. Long Vastus. (Fig. 129, 7.) 



Synonyms. Ischio-tibialis externus Girard. The biceps femoris and part of the 

 gluteus maximus of Man. ^The biceps abductor femoris of Percivall. Anterior pubio- 

 ischio-tibialis Leyli.} 



Volume Situation Extent Direction. This muscle offers an enor- 

 mous volume, as its name indicates ; it is situated behind the thigh and 

 the glutei muscles, and forming a curve with its concavity forwards, it 

 extends from the sacral spine to the superior extremity of the leg. 



Form and Structure. It is composed of two prismatic portions perfectly 

 distinct from each other for nearly the whole of their extent, lying side by 

 side, and designated as anterior and posterior. 



The anterior portion, the most considerable of the two, is very wide at 

 its upper extremity, and singularly contracted below. It is covered, on the 

 inferior half of its deep face, by a broad and strong tendinous band, which 

 becomes aponeurotic in ascending towards the superior extremity of the 

 muscle. Its component fibres are longest posteriorly, and all arise from the 

 superior extremity to be inserted into the tendinous layer. 



The posterior portion, much shorter than the preceding, presents an 

 inverse disposition, being contracted at its upper extremity and very 

 wide below. Its muscular fibres are partly attached, by their superior 

 extremities, to a longitudinal aponeurotic layer, which gives the muscle a 

 penniform appearance ; they terminate, inferiorly, in a strong aponeurosis 

 united to that of the fascia lata. 



Attachments. The anterior portion arises, by its superior extremity, from 

 the sacral spine, the sacro-ischiatic ligament, the aponeurosis enveloping the 

 coccygeal muscles, and the ischial tuberosity. It terminates : 1, On the 

 circular imprint situated behind the subtrochanterian crest, by a fibrous 

 branch detached from the deep tendon; 2, On the anterior face of the 

 patella, by the inferior extremity of that tendon. 



The posterior portion commences on the spine and tuberosity of the 

 ischium, where it joins the anterior division. Its terminal aponeurosis is 

 spread over the tibial muscles to constitute the fascia of the leg, and is 

 inserted into the tibial crest. 



