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THE CLAVICLE. 7g 
The sternal end (extremitas sternalis) is enlarged, and rests upon the meniscus 
of fibro-cartilage which is interposed between it and the clavicular facet on the 
upper and external angle of the manubrium sterni, as well as a small part of the 
inner end of the cartilage of the first rib. Its articular surface, usually broader 
Pectoralis major 
ACROMIAL Deltoid 
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DELTOID TUBERCLE 
Subclavius 
ARTERIAL FORAMEN RHOMBOLD IMPRESSION 
—COoNOID TUBERCLE 
Trapezius 
Fic, 123.—RiGHT CLAVICLE AS SEEN FROM BELOw. 
from above downwards than from side to side, displays an antero-posterior convexity, 
whilst it tends to be slightly concave in a vertical direction. The edge around 
the articular area which serves for the attachment of the capsule of the sterno- 
clavicular articulation is sharp and well defined, except below where it is rounded. 
The shaft is so curved that its anterior outline is convex in its inner two-thirds, 
whilst concave in the outer third of its length. Rounded or prismatic in form 
towards its sternal extremity, it becomes compressed and flattened towards its 
outer end. The superior surface of the shaft, which is smooth and subcutaneous 
throughout its whole length, is directed upwards and forwards; the inferior surface 
is inclined downwards and backwards. The anterior border, which separates the 
upper from the under surface in front, is rough and tubercular towards its inner 
end for the attachment of the clavicular fibres of the pectoralis major, whilst 
externally, where it becomes continuous with the anterior margin of the acromial 
end, it is better defined, and bears the imprint of the origin of the fibres of the 
deltoid muscle; here, not uncommonly, a projecting spur of bone, called the 
deltoid tubercle, may be seen. The posterior border is broad internally, where it is 
lipped superiorly to furnish an attachment for the clavicular fibres of the sterno- 
mastoid muscle; behind and below this the sterno-hyoid and _ sterno - thyroid 
muscles are attached to the bone. Externally, the posterior border becomes more 
rounded, and is confluent with the posterior edge of the acromial end at a point 
where there is a marked outgrowth of bone from its under surface, the conoid 
tubercle (tuberositas coracoidea). Into the outer third of this border are inserted 
the upper and anterior fibres of the trapezius muscle. The inferior surface of the 
shaft close to the sternal end is marked by an irregular elongated impression 
(tuberositas costalis), often deeply pitted for the attachment of the rhomboid 
ligament, which unites it to the cartilage of the first rib. External to this the 
shaft is channelled by a groove which terminates close to the conoid tubercle ; into 
this groove the subclavius muscle is inserted. 
The acromial end of the bone is flattened and compressed from above down- 
wards, and expanded from before backwards; its anterior edge is sharp and well 
defined, and gives attachment to the deltoid muscle, which also spreads over part 
of its upper surface. Its posterior margin is rougher and more tubercular, and 
provides a surface for the insertion of the trapezius. ‘The area between these two 
muscular attachments is smooth and subcutaneous. The outer edge of this 
forward-turned part of the bone is provided with an oval facet (facies articularis 
acromialis) for articulation with the acromion process of the scapula; the margins 
around this articular area serve for the attachment of the capsule of the joint. 
The inferior surface of the acromial end of the bone is traversed obliquely from 
behind forwards and outwards by a rough ridge or line called the trapezoid or 
oblique ridge. The posterior extremity of this ridge, as it abuts on the posterior 
border of the bone, forms a prominent process, the conoid tubercle (tuberositas 
coracoidea); to each of these, respectively, are attached the trapezoid and conoid 
portions of the coraco-clavicular ligament. 
