CLAVICLE. 201 



extremity, to part of the Sterno-hyoid muscle ; and presents, at or near the 

 middle, a foramen, directed obliquely outwards, which transmits the chief 

 nutrient artery of the bone. Sometimes, there are two foramina on the poste- 

 rior surface, or one on the posterior, the other on the inferior surface. The 

 inferior or subclavian surface is bounded, in front, by the anterior border; be- 

 hind by the subclavian border. It is narrow internally, but gradually increases 

 in width externally, and is continuous with the under surface of the flat por- 

 tion. Commencing at the sternal extremity may be seen a small facet for arti- 

 culation with the cartilage of the first rib. This is continuous with the articular 

 surface at the sternal end of the bone. External to this is a broad rough im- 

 pression, the rhomboid, rather more than an inch in length, for the attachment 

 of the costa-clavicular (rhomboid) ligament. The remaining part of this sur- 

 face is occupied by a longitudinal groove, the subclavian groove, broad and 

 smooth externally; narrow and more uneven internally; it gives attachment 

 to the Subclavius muscle, and, by its anterior margin, to the strong aponeu- 

 rosis which incloses it. Not unfrequently 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 in- 

 wards, and a little downwards and forwards ; and presents an articular facet, 

 concave from before backwards, convex from above downwards, which articu- 

 lates with the sternum through the intervention of an inter-articular fibre-car- 

 tilage; 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 car- 

 tilage of the first rib. 



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

 small, flattened, oval facet, which looks obliquely downwards and inwards, for 

 articulation with the acromion process of the scapula. The direction of this 

 surface serves to explain the greater frequency of dislocation upwards rather 

 than downwards, beneath the acromion process. The circumference of the arti- 

 cular facet is rough, especially above, for the attachment of the acromio-clavi- 

 cular ligaments. 



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

 clavicle 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 acquires considerable 

 bulk, becomes shorter, more curved, its ridges for muscular attachment become 

 prominently marked, and its sternal end of a prismatic form. The right cla- 

 vicle is generally heavier, thicker, and rougher, and often 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 

 project its own weight nearly two feet on a level surface, when a smart blow is 

 struck on it, and sufficient transverse elastic force, opposite the centre of its 

 anterior convexity, to throw its own weight about a foot. This extent of elastic 

 power must serve to moderate very considerably the effect of concussions re- 

 ceived 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 appears 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. 



