SK Kb ETON. 



SKELETON. 



2-1 



surfivoe there it another line corresponding to thia, and giving 

 origin to the uiylo-hyoMeus miuclo, whence it is called the Mylo- 

 Hyoidean ridge. On the inner surface there are also prominences 

 near the symphysis for the insertion of muscles. The lower border is 

 smooth and rounded ; the upper, or alveolar process, is marked by 

 notches corresponding with the sockets of the lower teeth, which are 

 et in it 



The rami ascend almost vertically from the ends of the two parts 

 of the body. They are broad, flat, and quadrilateral. At the angle 

 (5), where each joins the body, there are on both surfaces rough pro- 

 minences ; the external gives attachment to the maaseter, the internal 

 to the internal pterygoid muscle. The internal surface has also, near 

 the end of the mylo-hyoidean ridge, a hole, the inferior dental (6), 

 through which the nerve of the same name passes into the interior of 

 the jaw, from which it again emerge! at the mental hole (4). Leading 

 from the dental foramen U a email groove for a branch of the dental 

 nerve. The anterior border of the ramus terminates in a sharp pro- 

 jection, the Coronoid Process (7, 7), to which the temporal muscle is 

 attached ; the posterior, in a transversely oval process, with a smooth 

 summit, the Condyle (S, 8), which articulates with full freedom of 

 motion in the glenoid cavity of the temporal bone. Below this ia the 

 Keck (9), to which the external pterygoid muscle is in part attached; 

 and the space between the coudyle and the corouoid process is the 

 Sigmoid Notch (10, 10). 



The bones of the face serve as a groundwork to many parts whose 

 structures and functions are already described in separate articles ; 

 and since, in each case, the parts which the bones take are at the 

 same time considered, an account of their adaptation to the several 

 offices performed by the different portions of the face ia not hero 

 necessary. Their relations to the features are described in the article 

 MAX. 



The last main division of the Skeleton consists of the Upper and 

 Lower Extremities (n'j/. 1 ; 3, 4). The upper are composed of the 

 Scapula, Clavicle, Humerus, Radius, Ulna, Carpus, Metacarpus, and 

 Fingers. The scapula and clavicle are analogous to the Ossa Inno- 

 minata in the lower extremities. 



Fig. 22. 



The Scapula, or Shoulder-Blade, of which in fig. 22 the back is repre- 

 sented, with parts of the clavicle and humerus, is triangular in its 

 outline, and flat, being formed of two compact layers, and an inter- 

 mediate diploe, varied in thickness. It has three borders, or Costa; ; 

 a superior (1), posterior (2), which lies nearly parallel with the spine, 

 and an inferior (3), which is also the longest. They are all thicker 

 than the body of the bone, and give insertion to various muscles 

 moving the shoulder. From the posterior border, about one-third 

 from the upper and two-thirds from the lower angle, there commences 

 a ridge called the Spine (4), which, as it passes along the back of the 

 scapula towards the outer angle, gradually increases in depth, and at 

 it* end, projecting beyond and above the angle, bears a strong arched 

 process, called the Acromion (5), which articulates with the clavicle, 

 overhangs the shoulder-joint, and gives attachment to some of its 

 muscles and ligaments. The spine divides the back of the scapula 

 into two parts, of which the lower is much the larger, and which are 

 named, according to their position, Supra- (6) and Infra- (7) Spinous 

 FOUR. They give origin to muscles of the same names. The anterior 

 surface, or belly of the scapula, is slightly concave, and gives insertion 

 to the snWapularis muscle, for the attachment of whose several parts 

 it is marked by alternate longitudinal elevations and depressions. At 

 the outer angle the bone is terminated by the Olenoid Cavity (8), an 

 ovate surface slightly hollowed, narrower above than below, and with 

 which the hrad of the hnmerus (0) Articulates with very extensive 

 freedom of motion. Its border Is thick, and is rendered deeper in the 

 recent subject by a rim of fibro-cartilagc, the glenoid ligament, similar 

 to that which borders the acetabuluni. Between this border and the 

 base of the spine the scapular is narrower than elsewhere ; and this 

 part is called the Neck. From the superior costa, near this neck, a 



long and strong curved process, the Coracoid, projects forwards, and 

 gives attachment to several muscles and ligaments ; and at its root 

 there is in the superior costa a hole, or a notch, through which the 

 supra-scapular nerve (and sometimes its accompanying vessels) pass. 



The scapula is attached to the trunk only through the medium of 

 the clavicle, and by the muscles which connect it to the spine and 

 ribs. It can therefore slide freely on the back of the chest ; and, to 

 a certain extent, it follows all the larger movements of the humcrus, 

 so that its glenoid cavity, and the head of that bone, which have but 

 a small surface of mutual contact, almost always preserve the same 

 relation to each other, and are leas likely to be dislocated than they 

 would be if the scapula were more closely fixed. 



The Clavicle, or Collar-Bone, extends transversely from the notch 

 in the upper angle of the sternum to the anterior and outer margin 

 of the acromioQ (Jiy. 22). With both of these its ends arc articulated 

 with a moderate extent of mobility ; with the sternum, by the apex 

 of a broad triangular surface ; witli the acromion, by a small flat oval 

 surface on its posterior edge. The clavicle has nearly the directions of 

 the double-curved line of beauty, being slightly arched forwards at 

 the sternal, and backwards at the scapular, half. At the former it is 

 thick, strong, and triangular ; iu the latter, broad and flattened. On 

 the upper surface, which lies just under the skin, it is smooth ; on 

 the lower it has, near its sternal end, a mark where a ligament fixing 

 it to the first rib is attached ; farther out a larger elevation, to which 

 the subclavian muscle is fixed; and near the acromial end, other pro- 

 minences, to which the ligaments connecting it with the coracoid 

 process of the scapula (which projects just below it) ore affixed. 



The chief purpose of the clavicle is to keep the arm at a distance 

 from the trunk for all its outward motions ; and in adaptation to this, 

 its length and strength form one of the most characteristic features of 

 the human skeleton. 



The Humerus, 'the bone of the upper arm (fig. 23, A), ia articulated 

 above with the scapula by a hemispherical smooth portion called the 



Fig. 23. 



Head (1), which is bounded at its outer and lower part by a narrow 

 groove called the Neck. The axis of the head forms, with that of the 

 shaft or body of the bone, an angle of about 130. Close by the neck, 

 the upper and outer part of the shaft is surmounted by two Tubero- 

 alties : the larger and posterior (2) has three flat surfaces, to each of 

 which a muscle from the scapula ia attached ; the lesser (3) gives 

 attachment to the subscapularis muscle, Tho rest of the upper part 

 of the shaft is round and nearly smooth ; but just above the middle 

 of its outer surface is a rough elevation (4), to which the deltoid, the 

 chief muscle of the shoulder, is attached. About half-way down the 

 shaft begins to be flatter and wider, and at cither border of it com- 

 mence sharp ridges, which, as they descend, become prominent, and 

 which terminate below at the External (5) and Internal (6) Condyles. 

 Each of the condyles gives insertion to a ligament and several muscles 

 of the fore arm ; the inner is the more prominent, but the outer is 

 the larger. Between the condyles ia the inferior articular surface, 

 which is composed of two parts for articulating separately with each 

 of the bones of the fore arm. On the outer side, just within the 

 external condyle, the surface has a smooth rounded prominence or 

 tuberosity (7), against which the summit of the head of the radius is 

 apposcd ; more inwards there is a deep groove (8), separated from the 

 tuberosity by a slight ridge, and from the inner condyle by one much 

 more prominent, in which the raised portion of the aigraoid cavity of 

 the ulna moves as in a hinge-joint. This part of the joint is named 

 the Trochlea, Both before and behind it is bounded above by a 

 depression : into that on the posterior surface, which is the deeper, 

 the olecranon of the ulna is received when the fore arm ia extended ; 

 and into the anterior, the coronoid process of the same bone, when the 

 fore arm ia much bent. 

 The Fore Arm contains two bones, the Radius and the Ulna (fig. 23, 



