242 SKELETON. 



approaches the sciatic notch. The extreme point of this mo- 

 tion is the one preserved by the os femoris of the foetus utero. 



Extension is the reverse of flexion. When the latter has 

 been performed, extension restores the thigh bone to its verti- 

 cal position, and carries it some degrees farther, but cannot be 

 executed to the same extent behind, that flexion is in front. 

 When pushed to an extreme, it brings the trochanter major 

 under the inferior anterior spinous process of the ilium, and the 

 round ligament is put very much upon the stretch; it is, finally, 

 arrested by the lower part of the neck of the os femoris lodging 

 against the posterior elevated margin of the acetabulum, and 

 by the thickened part of the capsule, in front and above, being 

 so much distended as not to yield farther without laceration. 



Abduction is the act by which the thigh bones are separated. 

 When carried to an extreme, the under part of the head of the 

 os femoris leaves the acetabulum, and distends very forcibly 

 the capsular ligament at this point. The superior fasciculus 

 of the round ligament is strongly extended; but the inferior 

 fasciculus is kept easy, and, indeed, somewhat relaxed. This 

 motion is arrested by the trochanter major striking against the 

 ilium; without which it would be much more extensive, as the 

 capsular ligament is strained at its weakest point, and relaxed 

 at the strongest. 



Adduction is the reverse of the last. The muscles which 

 produce it, the adductors, from their situation and course, are 

 unable to give an extent to this motion much beyond the act of 

 reinstating the thigh when it has been abducted. In this re- 

 spect they are much less influential than the great pectoral 

 muscle which adducts the os humeri. The articular sur- 

 faces of the bones are suited to a much greater latitude of this 

 movement, but it is arrested both by a deficient power in the 

 muscles, and by the strong upper part of the capsular ligament 

 being put upon the stretch. 



Circumduction is the regular succession in a circle of the four 

 preceding motions, and is much less extensive in the os femoris 

 than in the os humeri, for the reasons stated. The centre of 

 the circle, or cone, thus described, is the head of the bone, and 



