BONES OF THE FOOT AS A WHOLE 



205 



A sesamoid also occurs in the tendon of the peroneus longus, where it glides over the groove 

 in the cuboid; another may be found, especially in later life, in the tendon of the tibialis anterior 

 over the first cuneiform bone, and another in the tendon of the tibialis posterior over the medial 

 surface of the head of the talus. Further a sesamoid, the fabella, sometimes occurs in the 

 lateral head of the gastrocnemius, and another may be found in the tendon of the ilio-psoas 

 over the pubis. 



BONES OF THE FOOT AS A WHOLE 



Although the foot is constructed on the same general plan as the hand, there 

 is a marked difference in its architecture to qualify it for the different functions 

 which it is called upon to perform. When in the erect posture, the foot forms a 

 firm basis of support for the rest of the body, and the bones are arranged in an 

 elliptical arch, supported on two pillars, a posterior or calcaneal pillar and an 



Fig. 



The centre for the 

 calcaneus appears at the tenth year; 

 consolidates at the sixteenth year 



252. — The Secondary Ossific Centres of the Foot. 



epiphysis for 



The centre for the epiphysis for the 

 metatarsal of the hallux appears at 

 the third year; consolidates at the 

 twentieth year 



The centres for the base of the ter- 

 minal phalanges appear at sixth 

 year, and consolidate at the eight- 

 eenth year 



Thfc centres for the heads of the metatarsals 

 appear at the third year, and consolidate at the twentieth year 



anterior or metatarsal pillar. It is convenient, however, to regard the anterior 

 part of the arch as consisting of two segments, corresponding to the medial and 

 lateral borders of the foot respectively. The medial segment is made up of the 

 three metatarsal bones, the three cuneiform, the navicular, and talus; the lateral 

 segment is made up of the fourth and fifth metatarsal bones, the cuboid, and the 

 calcaneus, and both segments are supported behind on a common calcaneal pillar. 

 The division corresponds to a difference in function of the two longitudinal arches. 

 Both are intimately concerned in ordinary locomotion. In addition, the medial, 

 characterised by its great curvature and remarkable elasticity, sustains the more 

 violent concussions in jumping and similar actions, whereas the lateral, less curved, 

 more rigid, and less elastic arch forms, with the pillars in front and behind, a 

 firm basis of support in the upright posture. 



Both arches are completed and maintained by strong ligaments and tendons. 

 The weakest part is the joint between the talus and navicular bone, and special 



