ANATOMY. 



225 



as a socket for the os brachii, and hence such ani- 

 mals as make much use of their fore legs, are fur- 

 nished with clavicles, as the ape, bear, bat, mouse, 

 badger, mole, &c. and an example may be seen 

 in plate LII. article Mammalia, in the Encyclo- 

 pedia, (fig. 13.) and the same plate, if carefully 

 examined in connection with the article which it 

 illustrates, will shed considerable light, not only 

 on human, but comparative osteology. The scap- 

 ula is very distinctly seen in the back view of 13. 

 fig. 2. ; 14. marking its spine, which is in the mid- 

 dle of its external surface, arising small from the 

 posterior edge of the scapula, becoming gradually 

 higher and broader as it reaches the anterior part 

 of the scapula, where it terminates in a broad, flat 

 process, called acromion, the anterior edge of 

 which forms an articulation for the clavicle ; the 

 situation of this is marked 15. fig. II. The 

 shoulder blade is of a triangular figure, situated on 

 the back and upper part of the ribs, forming the 

 posterior part of the shoulder, and so very thin as 

 to be transparent in its greatest extent. It is re- 

 tained in its situation merely by muscles, that unite 

 it to the head of the os hyoides, the ribs, the verte- 

 brae, and the upper arm bone ; and by means of these 

 muscles, it consequently has the power of moving 

 upwards, downwards, backwards ; it will there- 

 fore be obvious, how very necessary that its mo- 

 tions should be regulated by its connection with 

 the clavicle. None need be told that the shoulder 

 joint is one of considerable importance, and that 

 its motions are loose, movable, and very free, and 

 that it is even more liable to be luxated, or dis- 

 placed than any other joint in the human body. 

 It is formed by the large round head of the arm 

 bone, and shallow, articular cavity of the scapula, 

 the sides of which are elevated with cartilage, and 

 a capsular ligament, large, wide, and loose, is fixed 

 to the neck of the scapula and os brachii, and sur- 

 rounds the joint. Its almost constant movement 

 renders it requisite that it should be abundantly 

 supplied with synovia or joint oil, and for that pur- 

 pose, there are several bursse mucosse, opening into 

 it, independent of the natural secretion of the cap- 

 sular ligament. The motion of the joint is indeed 

 partially restrained, and rendered more secure by 

 the acromion process, which projects over it, and by 

 another process, called the coracoid process ; belo-w 

 a strong ligament likewise extends from one of 

 these processes to the other, and another ligament 

 extends from the acromion, to the capsule of the 

 joint, and farther security is derived from four 

 muscles, which are likewise inserted into the cap- 

 sular ligament. 



The Arm consists of one long bone, os brachii, 

 or os humeri, and occupies the space between the 

 junction of the clavicle and scapula with the fore 

 arm. It is a long cylindrical bone, having a round- 

 ed head on its superior part, and on the inferior 

 extremity are three processes, namely, an external 

 and internal condyle, and the trochleaof the bone, 

 on which the ulna moves. 



It is connected, as already stated, with the bones 

 of the shoulder, or, more correctly, its hemispheri- 

 cal head is received into the glenoid cavity of the 

 scapula, constituting a ball and socket joint. It 

 has several furrows, or cavities, which serve for 

 the attachment of muscles, not less than twenty-four 

 being attached to this bone; it is united to the 

 two bones of the forearm by means of a ginglymuo 

 joint. 



Fore Arm. The ulna. (17. fig. 2.) forms the 



VII. 



internal and posterior part of the fore-arm, and 

 the radius, (18. fig. 2.) the external and ante- 

 rior. The ulna, or larger bone, has a large upper 

 extremity, scooped out in front, forming what 

 is called the greater segmoid cavity, with which 

 it articulates with the base of the os brachii. 

 Below this apparent excavation by the coronoid 

 process, and above by the olecranon, or elbow, 

 upon which we lean. The ulna is a long bone, 

 and thicker above than below, and there is like- 

 wise a lesser sigmoid cavity at the side of the coro- 

 noid process, in which the rounded sides of the 

 head of the radius play. The lower end has a 

 rounded articular surface for the radius, and be- 

 neath a shallow cavity for an inter articular carti- 

 lage, the medium of connection with the wrist, and 

 its extreme point forms what is called the styloid 

 process. 



The radius, or lesser bone, is named from its 

 imaginary resemblance to the spoke of a wheel, or 

 to a measure used by the ancients. It is situated 

 on the outside of the forearm ; the body of the 

 bone inclines to a triangular form, the upper extre- 

 mity, or head, presenting a circular cavity, articu- 

 lating, as already stated, with the smaller condyle of 

 the os brachii. Its circumference joins with, and 

 turns in the smaller sigmoid cavity of the ulna ; 

 below this circular cavity the bone is contracted, 

 forming a neck, which terminates in the bicipital 

 tubercle, to which is fixed the biceps muscle. 

 The lower end of the radius has a superficial cav- 

 ity, articulating with the scaphoid and semilunar 

 bones of the wrist. On the inner side there is a 

 narrow concavity, in which the lower extremity of 

 the ulna rotates, and the extreme point of the 

 bone, like that of its fellow, is called the styloid 

 process. 



The first of these bones, the ulna, is, as has been 

 already stated, connected superiorly with the 

 trochlea of the brachii by arthrodia, inferior with 

 the carpus by arthrodia, and with the radius by 

 the trochoides.as in pronation, and supination. The 

 radius is connected with the brachia by ginglymus, 

 to the ulna by an inter osseous ligament and 

 trochoides, and to the carpus by arthrodia. Did 

 our limits permit, we might advert at considerable 

 length to the mechanism of the bones and joints 

 of the lower arm, to which two bones are attached 

 not fewer than twenty muscles ; but we must con- 

 tent ourselves with referring to Dr Paley, and his 

 noble, and learned, and ingenious commentators, 

 Lord Brougham, Sir C. Bell, T. Dick, LL. D., Dr 

 Roget, and Mr Paxton, to all of whom the public 

 at large, but especially juvenile inquirers, are under 

 the deepest obligation for the pains they have 

 taken to render anatomical and scientific details 

 pleasing and instructive to every class of readers. 



The Carpus, orWrist, is situated between the fore- 

 arm, and the metacarpus, and is composed of eight 

 bones, which lie close to one another in a double 

 row, one of which is superior and the other in- 

 ferior; and all these bones bear some resemblance 

 to the names given, or the things from which those 

 names are derived. In the superior row from the 

 thumb, to the little finger, are the os scaphoides, 

 or naviculare, lunare, cuneiform, and orbicular, 

 and in the lower row are the os trapezium, trapez- 

 oides, magnum and unciforme. The nature of 

 their union with the fore-arm has been already 

 stated, and they are connected with the metacar- 

 pus by arthrodia. A capsular ligament surrounds 

 them, and <he joint is strengthened by 

 I- 



