829 



SKELETON. 



SKELETON. 



830 



B, C) : the former being that with which the movements of rotation 

 are effected, the latter that which takes the chief part in flexion and 

 extension. The radius (B), when the palm of the hand is turned 

 forwards, is on the outer side of the arm ; and it is the shorter of the 

 two bones. At its upper end it has a circular disc, the Head (1), 

 hollowed on its upper surface, where it articulates with the tuberosity 

 on the lower end of the Humerus (A, 7), and smooth on its circum- 

 ference, where it is encircled by a ring, within which it rotates, and 

 which is formed in part by the ulna, and in part by a ligament. Just 

 below this is the Neck (2), of which the upper part is similarly encir- 

 cled ; and below it, on the anterior and inner surface, is a knob, the 

 Tubercle (3), to which the tendon of the biceps, the chief flexor muscle 

 of the fore arm, is attached. Yet lower, the shaft (6, 6) of the radius 

 becomes three-sided, and as it descends grows wider. At its lowest 

 part it is much expanded, is flattened before and behind, and termi- 

 nates with a prominent border, to which ligaments of the wrist-joiut 

 are attached. The posterior and outer surfaces of this lower end are 

 deeply grooved for the passage of tendons ; and the latter is prolonged 

 into a blunt-pointed process, the Styloid (4), to which the external 

 lateral ligament is attached. The inner surface has a small smooth 

 cavity, the Semilunar, which articulates with the outer part of the 

 lower head of the Ulna. The terminal surface (at 5) is smooth, some- 

 what triangular, and slightly hollowed; it articulates with the carpus, 

 and ia continuous over the inner border with that which articulates 

 with the ulna. 



The Ulna (C) is situated on the inner side of the fore arm. At its 

 upper and larger extremity it has a broad and deep crcscentic notch, 

 the Greater Sigmoid Cavity (1), whose smooth surface is divided into 

 two parts by a middle ridge, and which is received in the trochlea of 

 the humerus. It is bounded at either end by a sharp process. The 

 upper and posterior is the larger, and is named the Olecrauon (2) ; it 

 forms the rough prominence behind the elbow ; and when the arm is 

 extended, its point, which is curved forwards, rests in the fossa at 

 the back of the humerus. The lower and anterior (3) ia the Coronoid 

 Process, whose point, when the arm is fully bent, rests hi the anterior 

 fossa of the humerus. On the outer side the smooth surface of the 

 great sigmoid cavity ia continued over a small oval concave portion 

 of the side of the bone just behind the corouoid process. This is the 

 Lesser Sigmoid Cavity ; upon which the side of the head of the radius 

 rotates, and to whose borders the coronary ligament by which that 

 head is encircled is attached. The body or shaft (4, 4) of the ulna 

 grows smaller from above downwards, and is for the most part three- 

 sided ; its external and sharp margin giving origin to the iuterosseous 

 ligament, which, being attached also to the opposed margin of the 

 radius, fills up the space between these bones. At ita lower end the 

 ulna becomes nearly cylindrical, and then is a little enlarged : at its 

 termination it presents a double articular surface; one, on the end, 

 which is nearly circular, and (through the medium of a nbro-cartilage) 

 articulates with part of the carpus ; the other, on the outer border, 

 which is narrow and convex, and is received in the semilunar cavity 

 of the radius. The inner border of this lower extremity bears a short 

 and blunt process, the Styloid (5), to which the internal lateral ligament 

 of the wrist-joint is fixed. 



The motions of which the Fore-Arm is capable are Flexion and 

 Extension, and Kotation on its axis. The two former are effected at 

 the hiiige-like joint between the greater sigmoid cavity of the ulna 

 and the trochlea of the humerus; the head of the radius moving at 

 the same time forwards and backwards on the lower tuberosity. The 

 elbow affords the best specimen of a hinge-joint in the body, for no 

 lateral motion is permitted in it, the ulna being locked in the groove 

 between the two side-ridgea of the trochlea. Rotation, by which also 

 the rotation of the hand is effected, is performed by the upper head 

 of the radius moving round in the ring formed by the coronary liga- 

 ment and the lesser sigmoid cavity of the ulna; and by its lower 

 head at the same time being carried round on the outer border of the 

 lower head of the ulna. lu this movement the ulua is almost fixed, 

 its lower end only being carried outwards as that of the radius is 

 moved far inwards, when in extreme pronation of the hand the two 

 bones are made to cross each other. 



The Hand (23, D) consists of the Carpus, Metacarpus, and Fingers. 

 The Carpus (1) is composed of eight small bones arranged in two 

 rows, and so nearly immoveably united by ligaments, that, except in 

 being more elastic, they serve the purpose of a single bony arch. 

 Those of the first row, which lie nearest to the fore arm, are (from 

 the outer to the inner side) the Scaphoid, Lunar, Cuneiform, and 

 Pi-iform bones: those of the second row, following the same order, 

 are named Trapezium, Trapezoid, Magnum, and Uncitbrm. The three 

 first-named articulate with the radius directly, and with the ulna 

 indirectly ; the trapezium has a surface of peculiar form, concave 

 from side to side, and convex from before backwards, by which the 

 thumb, articulating with it, is permitted to have a very wide extent 

 of motion. 



The Metacarpus (between 2 and 2) is composed of five bones, which 

 are called by number according to the order in which they stand, 

 that of the thumb being taken as the first. Each is described as 

 consisting of a body and an upper ami lower heads. The form of the 

 upper head ia adapted to ono or inure of the bones of the carpus ; 

 that of the lower ia in all very convex, and rather narrow. The body 



is compressed from side to side, and is broader behind than before, 

 and on its dorsal than on its palmar aspect. The first metacarpal 

 bone only has free mobility. 



The bones of the fingers are called Phalanges. The thumb has 

 two, each of the fingers three. Their form and proportionate sizes 

 are plainly exhibited iufiy. 23, D. They are articulated with each 

 other, and with the metacarpal bones, so as to permit free extension 

 and flexion ; and at the joints between the phalanges and metacarpus 

 there is also permitted a dertain extent of lateral motion. At that 

 between the carpus and fore arm there is a very extensive hinge-like 

 motion of flexion and extension, as well as a wide lateral motion. 



The general arrangement of the bones of the human upper extremity 

 is adapted to a far more extensive and varied set of movements than 

 exists in the corresponding member of any other animal ; they have 

 all relation to the office of the hand, as an instrument not of support, 

 but of prehension, and that in iti moat perfect form. In this view 

 they are fully considered in the article MAN. 



Each of the Lower Extremities is formed by a Femur, Tibia, Fibula, 

 Patella, Tarsus, Metatarsus, and Toes. 



The Femur, or Thigh-Bone (fig. 24, A) is the largest of the body. It 

 articulates with the acetabulum of the Os Innominatum by ita head (1), 

 which forms rather more than half a sphere, and ia smooth, except 

 at its summit, where there is a depression for an interarticular liga- 

 ment. It rests upon a narrower part, the Neck (2), which descends 

 obliquely to the summit of the shaft, and is at its base somewhat 

 expanded. It is here set between two strong processes called Tro- 

 chanters, by which the shaft is aurmouuted ; and its base ia bordered 

 by two oblique lines, named Intertroehanteric, which pass on either 

 surface of the bone, from one to the other Trochanter. The Greater 

 Trochanter (3) is the uppermost, and lies at the outer part of the 

 bone ; it is thick, rough, and strong, and gives attachment to the great 

 muscles of the buttock. Behind it is a deep depression, the Digital 

 Fossa, in which the obturator and other muscles to rotate the thigh 

 outwards are attached. The Leaser Trochanter (4) ia on the inner 

 aspect of the femur, and also gives a point of insertion for muscles. 

 At the level of the Trochanters the shaft is flattened both behind and 

 before, but below them it ia round and nearly cylindrical, till, within 

 one-fourth of its length from the lower end, it expands, and again 

 becomes flattened. The shaft (5, 5) of each femur is directed rather 

 inwards, and is slightly arched forwards ; its axis makes, with that of 

 the neck and head, an angle of about 120; its surface is everywhere 

 smooth, except behind, where there is a prominent line, the Linea 

 Aspera, running along the middle, and at either end dividing into 

 two, which above go each to one of the troohauters, and below each 

 to one of the condyles. These condyles are the processes in which 

 the lower expanded part of the femur terminates. The inner condyle 

 (6) is the narrower, and descends lower than the outer (7), which is 

 the broader and stronger. Their articular surfaces are united in front 

 at a concave pulley-like surface (8), over which the patella lies : below 

 it they diverge, and at the back of the femur are separated widely on 

 two very convex prominences, between which there is a deep and 

 rough fossa, in which the crucial ligaments of the knee-joint are fixed. 

 On the sides of the femur, just above the lower border of the coudyle, 

 are eminences, the Tuberosities (9, 9), to which the external and 

 internal lateral ligaments respectively are attached. 



The Tibia, or Shin-Bone (jig, 24, B), is placed on the front and inner 



