STANDING. 591 



forward that the line of gravity passes through the line connecting the 

 posterior borders of the knee-joints, must now be fixed at the knee- 

 joints. Falling backward is prevented by the strength of the quad- 

 riceps femoris, supported by the tension of the fascia lata. Indirectly, 

 the ilio-femoral ligament is believed also to aid in preventing falling 

 backward, because in this act the thigh must be rotated outward, and this 

 is prevented by the tension of the ligament named in the upright posi- 

 tion. Lateral flexion at the knee-joint is impossible on account of the 

 arrangement of the hinge -joint, strengthened by the strong lateral liga- 

 ments of the knee. Rotation at the knee-joint is impossible in the ex- 

 tended position. 



5. The center of gravity of the entire body is situated 4.5 cm. in a 

 vertical line below the promontory of the sacrum. A perpendicular 

 dropped from this point strikes the ground a little in front of the line 

 connecting both ankle-joints. The body would, therefore, fall forward 

 at the latter joints. This is prevented by the muscles of the calf, aided 

 by the muscles of the deep layer, namely the tibialis posticus, the flexors 

 of the toes, and the peroneus longus and brevis. 



The following additional factors have also been considered worthy of mention : 

 (a) As the longitudinal axes of the feet form an angle of 50 at the heels, falling 

 forward can take place only if the feet have taken a position more nearly parallel 

 to their longitudinal axes. (6) Falling forward is opposed also by the form of 

 the articular surfaces of the foot, as under such circumstances the anterior, broader 

 part of the astragalus would have to be pressed between the two condyles. This 

 last factor is actually of little importance, as falling forward does not require 

 such a marked change of position as would be necessary to bring this mechanism 

 into play. 



6. The tarsal and metatarsal bones, united by tense ligaments, form 

 the arch of the foot. This touches the ground at three points, the tuber- 

 osity of the os calcis, the head of the first metatarsal, and the head of the 

 fifth metatarsal bone. Between the last two points, however, the heads 

 of the other metatarsal bones also form points of support. .The weight 

 of the body falls upon the highest point of the arch, the head of the as- 

 tragalus. The arch of the foot is maintained only by ligaments. The 

 toes are able materially to aid in balancing the body by means of their 

 muscle-play. Standing erect causes more fatigue than walking. 



Braune and Fischer have recently distinguished the following varieties of 

 station, for which, in contradistinction from the foregoing older exposition, a 

 different form of muscular activity is required, (i) The "normal position" is 

 characterized by the fact that the line of gravity passes downward through the 

 lines connecting the central points of both hip- joints, knee-joints, and ankle- 

 joints, and passes upward through the centers of gravity of the trunk and the 

 head. Accordingly, the body need only be stiffened; no muscular activity at all 

 is required to prevent falling forward or backward. (2) In the "comfortable 

 position" the line of gravity strikes the ground in front of the line connecting 

 the centers of both ankle-joints at a point corresponding approximately to the 

 anterior border of the ankle-joint. Hence, muscular action is necessary to prevent 

 falling forward at the ankle-joints. (3) In the "military position" the line of 

 gravity falls in front of the knee-joints and ankle-joints, striking the ground at 

 a point corresponding approximately to the middle of the sole. Hence, falling 

 forward must be prevented at both joints, and this induces great fatigue on account 

 of the considerable and continuous muscular exertion. 



The position of the center of gravity in the living person is determined as 

 follows: The body is placed on a narrow board the length of the body. A balanc- 

 ing edge is placed beneath the board, and first the upper and lower halves are 

 balanced, then the right and left halves. Finally, the body is balanced when 

 standing upright on a small 'board. The center of gravity is situated at the 



