ARCHES OF THE FOOT 



1203 



arches in the following important particulars (Hunii>hry): {a) in not being 

 wedge-shaped; (/v) in not being so placed as to su])port and receive support from 

 the two halves of the arch: in front tlie astragalus does fulHl this condition 1)V 

 fitting into the scaphoid; behin<l, it overlaps the ealcaneum without at all sup])(.i-t 

 hig it; (c) this areh and the su])i)()rt of its keystone largely depend on ligaments 

 and tendons; (//) it is a mobile keystone: to give it chances of shifting its i)ressure, 

 and so ol)taining rest, its e(piilil)riuni is not always maintained in one jjosition. 



(B) Transverse arch (fig. 708). — This is best marked about the centre of the 

 foot, at the instep, ah nig the tarso-metatarsal joints. This, as well as the longitu- 

 dinal arch, yields in walking, and so gives elasticity and spring. 



Uses of the arches. — (1) They give combined elasticity and strength to the 

 tread. Thus they give firmness, free (piickness, and dignity, l)oth in standing and 

 walking, instead of what we see in their absence, viz. the lameness of an artificial 

 limb, and the shuifling or hobbling which goes with tight l)00ts, deformed toes, 

 fiat-foot, bunions, corns, etc.; (2) they protect the plantar vessels, nerves, and 

 muscles; (o) they add to man's height; (4) they make his gait a i)erfect combina- 



FiG. 7(5S.— This shows the Effect of Muscular Action in thkowixg up the Arch. 



Tendo Aehillis 



Tibialis posticus 



Flexor longus halluces 



tion of plantigrade and digitigrade, as is seen in man's walking, wlien he uses first 

 the heel. tlii'U all the foot, and then the toes (Humphry). 



Maintenance of the arch. — (1) Plantar fascia. — This is (a) a binding tie 

 between tlie pillars of the longitudinal arch; (/>) it protects the structures beneath; 

 (c) it is a self-regulating ligament and protection. Thus, having a quantity of 

 muscular tissue attached to its ui)i)er and back part, it constantly responds by the 

 contraction of this, to the amount of any i)ressure made upon the foot. (2) 

 Calcaneo-scaphoid ligament. — This is a thick plate of fibrous tissue, partly 

 elastic, attached to the under surface of the ealcaneum, sustentaculum tali, and 

 scaphoid. It is thickest at its inner side, where it blends with the anterit»r part of 

 the deltoid ligament, and where the tibialis posticus jiasses into the sole, giving 

 much sui)port to the head of the astragalus, ami assisting the jiower and s])ring of 

 this ligament {vide infra). (3) Calcaneo-cuboid ligaments, (n') Long; (h) 

 short. — These ligaments are the main su]>port i>t' the outer, firm, and less elastic 

 part of the longitudinal arch. (4) Tibialis posticus. — The reason of this muscle 

 having so manv insertions below is to l»race together the tarsal bones, and to jirevent 



