212 



THE SKELETON. 



is more solidly constructed, and its component parts are less movable on each other 

 than in the hand. This is especially the case with the great toe, which has to 

 assist in supporting the body, and is therefore constructed with greater solidity ; it 

 lies parallel with the other toes, and has a very limited degree of mobility, whereas 

 the thumb, which is occupied in numerous and varied movements, is constructed 

 in such a manner as to permit of great mobility. Its metacarpal bone is directed 

 away from the others, so as to form an acute angle with the second, and it enjoys 

 a considerable range of motion at its articulation with the carpus. The foot is 

 placed at right angles to the leg a position Avhich is almost peculiar to man, and 

 has relation to the erect position which he maintains. In order to allow of its 

 supporting the weight of the whole body in this position with the least expenditure 

 of material, it is constructed in the form of an arch. This arch is not, however, 

 made up of two equal limbs. The hinder one, which is made up of the os calcis 

 and the posterior part of the astragalus, is about half the length of the anterior 

 limb, and measures about three inches. The anterior limb consists of the rest of 



Appears 10th year ; 

 unites after puberty. 



Tarsus. 



One centre for each bone, 

 except os calcis. 



Appears 5th year. 

 Unite 18th-20 ye&T 



-Appears 7th week. 



Metatarsus. 

 Tivo centres for each bone : 

 One for shaft, 

 One for digital extremity 

 except 1st. 



Appears 7th week.~ 



fa 



Unite 18th-20th year. 

 Appears 3rd year. 



Appears 4th year. 

 Unite 17-18th year. f 

 Phalanges. Appears 2nd-4th month.- 

 Two centres for each bone : 

 One for shaft, 



One for metatarsal Appears 6th-7th yea 

 extremity. Unite mh-18th year. 



Appears 2nd- 4th month. 



Appears 6th year. 



Unite 17th-18th year. 



Appears 7th week. 



FIG. 151. Plan of the development of the foot. 



the tarsal and the metatarsal bones, and measures about seven inches. It may be 

 said to consist of two parts, an inner segment made up of the head of the astragalus, 

 the navicular, the three cuneiform, and the three inner metatarsal bones ; and an 

 outer segment composed of the os calcis, the cuboid, and the two outer metatarsal 

 bones. The summit of the arch is at the superior articular surface of the astragalus ; 

 and its two extremities that is to say, the two piers on which the arch rests in 

 standing are the tubercles on the under surface of the os calcis posteriorly, and 



