STANDING AND SITTING. 505 



position of the processes also influences greatly the mobility. The strongly depressed spines of 

 the dorsal region hinder hyperextension. The articular processes on the cervical vertebrse are 

 so placed that their surfaces look obliquely from before and upwards, backwards, and down- 

 wards ; this permits relatively free movement, rotation, lateral and nodding movements. In 

 the dorsal region, the articular surfaces are directed vertically and directly to the front, the 

 lower directly backwards ; in the lumbar region, the position of the articular processes is almost 

 completely vertical and antero-posterior. In bending backwards as far as possible, the most 

 mobile parts of the column are the lower cervical vertebrae, the 11th dorsal to the 2nd lumbar 

 and the lower two lumbar vertebra (E. If. Weber). 



3. The centre of gravity of the head, trunk, and arms when fixed as above, lies in front of 

 the 10th dorsal vertebra. It lies further forward, in a horizontal plane, passing through the 

 xiphoid process, the greater the distension of the abdomen by food, fat, or pregnancy. A line 

 drawn vertically downwards from the centre of gravity passes behind the line uniting both hip- 

 joints. Hence, the trunk would fall backwards on the hip-joint, were it not prevented partly 

 by ligaments and partly by muscles. The former are represented by the ileo-femoral band and 

 the anterior tense layer of the fascia lata. As ligaments alone, however, never resist permanent 

 traction, they are aided, especially by the ileo-psoas muscle inserted into the small trochanter, 

 and in part, also, by the rectus femoris. Lateral movement at the hip-joint, whereby the one 

 limb must be abducted and the other adducted, is prevented especially by the large mass of the 

 glutei. When the leg is extended, the ileo-femoral ligament, aided by the fascia lata, prevents 

 adduction. 



4. The rigid part of the body, head, and trunk, with the arms and legs, whose centre of 

 gravity lies lower and only a little in front, so that the vertical line drawn downwards inter- 

 sects a line connecting the posterior surfaces of the knee-joints, must now be fixed at the knee- 

 joint. Falling backwards is prevented by a slight action of the quadriceps femoris, aided by 

 the tension of the fascia lata. Indirectly it is aided also by the ileo-femoral ligament. Latei-al 

 movement of the knee is prevented by the disposition of the strong lateral ligaments. Rotation 

 cannot take place at the knee-joint in the extended position ( 305, I., 3). 



5. A line drawn downwards Trom the centre of gravity of the whole body, which lies in the 

 promontory, falls slightly in front of a line between the two ankle-joints. Hence, the body 

 would fall forward on the latter joint. This is prevented especially by the muscles of the calf, 

 aided by the muscles of the deep layer of the leg (tibialis posticus, flexors of the toes, peroneus 

 longus et brevis). 



Other Factors : (a) As the long axis of the foot forms with the leg an angle of 50, falling 

 forward can only occur after the feet are in a position more nearly parallel with their long axis. 

 (b) The form of the articular surfaces helps, as the anterior broad part of the astragalus must be 

 pressed between the two malleoli. The latter mechanism cannot be of much importance. 



6. The metatarsus and phalanges are united by tense ligaments to form the arch of the foot, 

 which touches the ground at three points tuber calcanei (heel), the head of the first metatarsal 

 bone (ball of the great toe), and of the fifth toe. Between the latter two points, the heads of 

 the metatarsal bones also form points of supports. The weight of the body is transmitted to 

 the highest part of the arch of the foot, the caput tali. The arching of the foot is fixed only by 

 ligaments. The toes play no part in standing, although, when moved by their muscles, they 

 greatly aid the balancing of the body. The maintenance of the erect attitude fatigues one 

 more rapidly than walking. 



309. SITTING. Sitting is that position of equilibrium whereby the body is supported 

 on the tubera ischii, on which a to and fro movement may take place (H. v. Meyer). The 

 head and trunk together are made rigid to form an immovable column, as in standing. "We 

 may distinguish (1) the forward posture, in which the line of gravity passes in front of the 

 tubera ischii ; the body being supported either against a fixed object, e.g., by means of the arm 

 on a table, or against the upper surface of the thigh. (2) The backward posture, in which the 

 line of gravity falls behind the tubera. A person is prevented from falling backward either by 

 leaning on a support, or by the counter- weight of the legs kept extended by muscular action, 

 whereby the sacrum forms an additional point of support, while the trunk is fixed on the thigh 

 by the ileo-psoas and rectus femoris, the leg being kept extended by the extensor quadriceps. 

 Usually the centre of gravity is so placed that the heel also acts as a point of support. The 

 latter sitting posture is of course not suited for resting the muscles of the lower limbs. (3) 

 When " sitting erect " the line of gravity falls between the tubera themselves. The muscles of 

 the legs are relaxed, the rigid trunk only requires to be balanced by slight muscular action. 

 Usually the balancing of the head is sufficient to maintain the equilibrium. 



310. WALKING, RUNNING, AND SPRINGING. By the term walking 

 is understood progression in a forward horizontal direction with the least possible 

 muscular exertion, due to the alternate activity of the two legs. 



Methods. The Brothers Weber were the first to analyse the various positions of the body in 

 walking, running, and springing, and they represented them in a continuous series, which 



