128 



THE POPULAR EDUCATOR. 



the composition of which it does not enter ; the lower extremity 

 is pyramidal in shape, connected to the side of the tibia by the 

 strong inter-osseous ligament, and articulating by a smooth 

 surface with the side of the astragalus, forming the outer ankle, 

 which is more prominent and extends lower down thau that on 

 the inner side. 



Lying over and protecting the front of the knee, not articu- 

 lated to either of the bones, but held in position by the tendon 

 of a strong muscle, is a small heart-shaped 

 bone, the patella or knee-cap. This helps to 

 complete the knee-joint, and also gives extra 

 leverage to the extensor muscles of the thigh. 



The foot, the terminal division of the lower 

 extremity, is like the hand composed of twenty- 

 seven bones, and is also divisible into three 

 parts the tarsus, metatarsus, and phalanges. 



The tarsus consists of seven bones, the 

 largest of which, the os calcis, a massive 

 irregularly-shaped bone, forms the hinder 

 portion, and projects backwards to make the 

 heel. In front of the os calcis is a pyrami- 

 dal-shaped bone, 

 the cuboid ; this 

 forms the greater 

 portion of the 

 outer side of the 

 foot, and articu- 

 lates in front with 

 two of the meta- 

 tarsal bones. 

 Superimposed on 

 the os calcis is 

 the next largest 

 bone of the foot, 

 the astragalus, 

 the rounded upper 

 surface of which 

 articulates with 

 the lower extre- 

 mity of the tibia, 

 and its lateral 

 3urfaces with 

 that bone and the 

 fibula forming 

 the ankle-joint. 

 In front of the 

 ankle-joint is a 

 boat-shaped bono, 

 the scaphoid, and 

 again in front of 

 that three wedge- 

 shaped bones, the 

 cuneiform. The 

 bones of the 

 tarsus articulate 

 laterally with 

 each other, and 

 are so arranged as 

 to- form a very 

 powerful arch. 



The metatarsal 

 bones are five in 

 number, and arti- 

 culate posteriorly 

 with the tarsal 

 bones (the cuboid 

 and cuneiform), 

 in front with the phalanges, of which there are, as in the -hand, 

 fourteen, each toe having three, except the great toe, which has 

 only two. 



Having now considered the elements of which both the 

 extremities are composed we shall be able better to understand 

 the analogies between them, and the modifications of structure 

 necessary to fulfil their differing functions. The purpose of 

 the upper extremity is mainly that of prehension and touch, and 

 consequently great freedom of movement in its various articu- 

 lations is needed. The lower extremity, on the other hand, 

 being designed to bear the whole weight of the trunk and for 



progression, requires that all its component parts should be of 

 great strength. And so we find that whilst all the bones of the 

 lower extremity are larger and more massive than those of the 

 upper, the articulations of the upper permit much greater 

 mobility than those of the lower extremity. Look at the 

 difference between the shoulder and tho hip joint : in the former 

 the scapula moves freely on the trunk, and the humerus moves 

 freely in almost every direction in its shallow cup, the glenoid 

 cavity ; in the lower extremity the haunch 

 is a fixture, and the head of the femur sinks 

 deeply into its socket, and is held in its 

 position by the ligament that has been 

 mentioned, thus adding greatly to the 

 strength of the joint, but at the expense of 

 its mobility. 



Then again in the upper extremity the 

 greatest amount of movement is all in one 

 direction the hand bends on tho fore-arm, 

 the fore-arm on the arm, and the arm on 

 the trunk ; in the leg it is alternated, the 

 thigh is flexed across the trunk, but the leg 

 is flexed, not on 

 the thigh, but 

 backwards on to 

 the ham, whilst 

 the foot is flexed 

 on the front of 

 the leg. The first 

 arrangement ena- 

 bles the arm to 

 be more efficient- 

 ly used as a pro- 

 tection to the head 

 and chest ; by the 

 latter the lower 

 extremity is con- 

 verted into a kind 

 of double spring, 

 which serves a 

 great end in loco- 

 motion, and ena- 

 bles the limbs 

 better to break 

 the force of a con- 

 cussion. 



The hand and 

 foot also differ in 

 some material 

 points : the hand 

 is loosely articu- 

 lated in a straight 

 line with the rest 

 of the extremity, 

 it is narrow and 

 long, the fingers 

 also are long and 

 tapering, whilst 

 the thumb, very 

 loosely jointed, is 

 placed diverging 

 from the rest of 

 the hand; these 

 are so to enable 

 the hand to fulfil 

 its end, that of 

 grasping and 

 touch, and to 



enable it to perform the manifold and differing movements 

 which are required of it : so varied indeed are these movements, 

 that it may be said to speak a language of its own, a tongue 

 that is understood of all men. The foot, designed for loco- 

 motion and as a base on -vhich the body rests, is more firmly 

 articulated at right angles with the leg ; it is broad and short, 

 the toes also being small and short, and posteriorly the heel 

 acts as a powerful lever. 



We have now completed our survey of the osseous system, 

 and must pass on to consider tho next portion of our subject, 

 the muscular system or fleshy portion of the body. 



V. THE HUMAN SKELETON. VI. THE UPPER EXTBEMITY. VII. THE LOWEK EXTREMITY. 

 Eefs. to Nos. in Figs. V. 1, skull ; 2, thorax ; 3, pelvis. VI. 1, humerus ; 2, ulna ; 3, radius ; 4, 

 carpus; 5, metacarpus; 6, phalanges. VII. 1, femur; 2, patella; 3, tibia; 4, fibula; 5, 

 tarsus ; G, metatarsus ; 7, phalanges. 



