49 2 



APPLIED ANATOMY. 



The connection of the lower extremities with the trunk is through the means of 

 the pelvic girdle and spinal column ; therefore the pelvis and vertebrae above exert a 

 marked influence on the extremities below and must be taken into consideration. 

 The normal upright position of man is obtained by maintaining a proper balance. 

 This balance can be disturbed either anteroposteriorly or laterally. The lower limbs 

 are placed laterally, one on each side; this gives greater stability in that direction, so 

 that when a person falls it is usually in a forward or backward direction rather than 

 toward the side. 



Anteroposterior Equilibrium. In the upright position the highest joint is 

 that between the occiput and atlas and the lowest that of the ankle; to enable the 

 body to be in a state of rest, in the upright position, with the use of the least amount 



B. 



FIG. 494. Anteroposterior equilibrium. 



:rtical 



equilibrium and it falls. 



Fig. D. If the body, as occurs in some diseases and injuries, is inclined so far forward as to bring the vertic 

 line a-b through the centre of gravity c, in front of the base of support d-e, then it is in a state of unstable equilibriu 

 and additional support is used, in the form of a cane, to prevent falling forward. 



of muscular exertion these joints are placed almost vertically one above the other. 

 For the same reason if any part of the skeleton lies in front of a line joining the 

 condyle of the occiput with the astragalo-scaphoid joint it is counterbalanced by a 

 projection toward the opposite side. Thus the anterior curve of the cervical region 

 is followed by the posterior curve of the dorsal; the anterior of the lumbar, by the 

 posterior of the sacral. The hip-joint has its centre of motion slightly behind the 

 centre of gravity as has also the knee. A vertical line through the center of gravity 

 must fall within its base of support. This latter is formed by the arch of the foot ; its 

 two ends are the tuberosity of the calcaneum posteriorly and the head of the first 

 metatarsal bones anteriorly. The body is in the position of greatest stability when 

 the centre of gravity is midway between those two points, which is when it passes 

 through the astragalo-scaphoid joint. As the line of gravity passes from the centre of 



