1202 



SURGICAL AXD TOPOGRAPHICAL ANATOMY 



malleolus, supplies tlie inner border of the foot as far as the middle of the 

 inste]>. 



Plantar arteries. — The line of the internal would be one drawn from the 

 ])ifureation of the posterior tibial, or about midway between the tip of the internal 

 malleolus and the inner border of the heel, to the middle of the plantar surface of 

 the great toe. The course of the external plantar runs in a line drawn from the 

 l>ifurcation, first obliijUely across the foot to a i)oint a little internal to the inner 

 side of the base of the tifth metatarsal, and thence obliciuely across the foot till it 

 reaches the first space and joins with a communicating branch from the dorsal 

 artery. It thus crosses the foot twice. In the first part, it is more superficial, in 

 the second very deep; it here forms the plantar arch, and is only separated from 

 the bases of the metatarsals bv the interossei. 



ARCHES OF THE FOOT 



These are two — the longitudinal and the transverse. 



(A) Longitudinal arch (figs. 766, 767, and 76S). — This is by far the most 

 important. Extent : From the heel to the heads of the metatarsal l:)ones. The toes 

 do not add much to the strength and elasticity of the foot (Humphry). They en- 

 large its area and adapt it to inequalities of the ground, are useful in climbing, and 



Fig. 767.— The Aech in the Ordixaey Posmox of Standing. (Ellis, of Gloucester, 



Muscles going to form the 

 teudo Achillis 



Tibialis posticus 



'in giving an impulse to the step before the foot is taken from the ground, in the third 

 stage of walking. Two pillars. — Professor Hum]iliry lays stress on the important 

 diflferences between these two: (1) Posterior pillar; This consists of the calca- 

 neum and hinder part of the astragalus, viz. only two bones in order to secure 

 solidity, and to enable the calf-muscles to act directly upon the heel, without any 

 of that loss of ])ower whidi would be brought ai)out by many moving joint- 

 surfaces. (2) Anterior pillar : Here there are many liones and joints to jirovide 

 (a) elastic springiness, and (h) width. This anterior pillar may again l)e divided 

 into two: (a) An inner pillar, very elastic, consisting of the astragalus, scaphoid, 

 three cuneiforms, and three inner metatarsals, (b) An outer, formed l)y the 

 cuboids and two outer metatarsals. This is stronger and less elastic, and tends to 

 buttress up the inner pillar. Keystone : This is represented by the summit of 

 the trochlear surface of the astragalus. It differs from the keystones in ordinary 



