136 



THE SKELETON. 



Platysma ; but, corresponding to the inner half of the bone, it is divided by a more 

 or less prominent line into two parts : a lower portion, elliptical in form, rough, 

 and slightly convex, for the attachment of the Pectoralis major ; and an upper 

 part, which is rough, for the attachment of the Sterno-cleido-mastoid. Between 

 the two muscular impressions is a small subcutaneous interval. The posterior or 

 cervical surface is smooth, flat, and looks backward toward the root of the neck. 

 It is limited, above, by the superior border; below, by the subclavian border; 

 internally, by the margin of the sternal extremity ; externally, it is continuous 

 with the posterior border of the flat portion. It is concave from within outward, 

 and is in relation, by its lower part, with the suprascapular vessels. This surface, 

 at about the junction of the inner and outer curves, is also in close relation with 

 the brachial plexus and subclavian vessels. It gives attachment, near the sternal 

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

 a foramen, directed obliquely outward, which transmits the chief nutrient artery 

 of the bone. Sometimes there are two foramina on the posterior surface, or one 

 on the posterior, the other on the inferior surface. The inferior or subclavian 



Acromial extremity. 



Sternal extremity. 



FIG. 92. Left clavicle. Superior surface. 



surface is bounded, in front, by the anterior border ; behind, by the subclavian 

 border. It is narrow internally, but gradually increases in width externally, and 



FIG. 93. Left clavicle. Inferior surface. 



is continuous with the under surface of the flat portion. Commencing at the 

 sternal extremity may be seen a small facet for articulation 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 surface, the rhomboid impression, 

 rather more than an inch in length, for the attachment of the costo-clavicular 

 (rhomboid) ligament. The remaining part of this surface is occupied by a longi- 

 tudinal groove, the subclavian groove, broad and smooth externally, narrow and 

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

 margins to the costo-coracoid membrane, which splits to enclose a muscle. Not 

 infrequently 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 extremity of the clavicle is triangular in form, directed 



