SCAPULA. 123 



narrow and more uneven internally; it gives attachment to the Subclavius muscle, 

 iiinl by its anterior margin, to the strong aponeurosis which incloses it. Not 

 unfrequeiitly this groove is subdivided into two parts, by a longitudinal line, 

 which gives attachment to the intermuscular septum of the Subclavius muscle. 



The internal or sternal end of the clavicle is triangular in form, directed inwards, 

 nnd a little downwards and forwards ; and presents an articular facet, concave 

 from before backwards, convex from above downwards, which articulates with 

 the sternum through the intervention of an iriterarticular fibre-cartilage ; the 

 circumference of the articular surface is rough, for the attachment of numerous 

 ligaments. This surface is continuous with the costal facet on the inner end of 

 the inferior or subclavian surface, which articulates with the cartilage of the 

 first rib. 



The outer or acromial extremity, directed outwards and forwards, presents a 

 small, flattened, oval facet, directed obliquely downwards and inwards, for articu- 

 lation with the acromion process of the scapula. The direction of this surface 

 serves to explain the greater frequency of dislocation of this bone upon, and not 

 beneath, the acromion process. The circumference of the articular facet is rough, 

 especially above, for the attachment of the acromio-clavicular ligaments. 



Peculiarities of the Bone in the /Sexes and in Individuals. In the female, the cla- 

 vicle is generally less curved, smoother, and more slender than in the male. In 

 those persons who perform considerable manual labor, which brings into constant 

 action the muscles connected with this bone, it requires considerable bulk, becomes 

 shorter, and more curved, its ridges for muscular attachment become prominently 

 marked, and its sternal end of a prismatic or quadrangular form. The right 

 clavicle is generally heavier, thicker, and rougher, and ofte*n shorter, than the left. 



Structure. The shaft, as well as the extremities, consists of cancellous tissue, 

 invested in a compact layer much thicker in the centre than at either end. The 

 clavicle is highly elastic, by reason of its curves. From the experiments of Mr. 

 Ward, it has been shown that it possesses sufficient longitudinal elastic force to 

 raise its own weight nearly two feet on a level surface ; and sufficient transverse 

 elastic force, opposite the centre of its anterior convexity, to raise its own weight 

 about a foot. This extent of elastic power must serve to moderate very consi- 

 derably the effect of concussions received upon the point of the shoulder. 



Development. By two centres : one for the shaft, and one for the sternal extremity. 

 The centre for the shaft appea-rs very early, before any other bone ; the centre 

 for the sternal end makes its appearance about the eighteenth or twentieth year, 

 and unites with the rest of the bone a few years after. 



Articulations. With the sternum, scapula, and cartilage of the first rib. 



Attachment of Muscles. The Sterno-cleido-mastoid, Trapezius, Pectoralis major, 

 Deltoid, Subclavius, and Sterno-hyoid. 



THE SCAPULA. 



The Scapula forms the back part of the shoulder. It is a large flat bone, tri- 

 angular in shape, situated at the posterior aspect and side of the thorax, between 

 the first and eighth ribs, its posterior border or base being about an inch from, 

 and nearly parallel with, the spinous processes of the vertebrae. It presents for 

 examination two surfaces, three borders, and three angles. 



The anterior surface or venter (fig. 84) presents a broad concavity, the sub- 

 scapular fossa. It is marked, in the posterior two-thirds, by several oblique ridges, 

 which pass from behind obliquely forwards and upwards, the anterior third being 

 smooth. The oblique ridges, above-mentioned, give attachment to the tendinous 

 intersections ; and the surfaces between them, to the fleshy fibres of the Subscapu- 

 laris muscle. The anterior third of the fossa, which is smooth, is covered by, 

 but does not afford attachment to, the fibres of this muscle. This surface is sepa- 

 rated from the posterior border by a smooth triangular margin at the superior 

 and inferior angles, and in the interval between these, by a narrow edge which is 



