ANATOMY IN A NUTSHELL. 37 



cavity anterior at the acromial extremity. It is more often broken than any 

 other bone in the body and when broken will press upon the Brachial Plexus 

 producing temporary paralysis. It has but one epiphysis, which is at the 

 sternal extremity, hence the nutrient artery runs towards the acromial extrem- 

 ity (Rule 2, Lesson 1.) The bone is divided into an inner two-thirds 

 which is somewhat triangular on cross-section, and an outer one-third which 

 is more flattened from above downward; the coracoid process of the scapula is 

 under this division of the clavicle. (Plates X-XI.) 



Outer one-third. — The upper extremity of this portion has the attachment 

 of the Deltoid muscle in front and the Trapezius behind, with a small interval 

 between them. The under surface has first a conoid tubercle near the poster- 

 ior border and internal boundary of this part of the bone. The conoid liga- 

 ment passes from this tubercle to the coracoid process of the scapula, which is 

 immediately under it. Second, the trapezoid, or oblique line, sometimes a 

 furrow, passes from the conoid process forward and outward and gives attach- 

 ment to the trapezoid ligament. The conoid and trapezoid ligaments make 

 the coraco-clavicular ligament. The anterior border is concave and gives at- 

 tachment to the Deltoid; this border has a deltoid tubercle. The posterior 

 border is broader than the anterior one; it is convex and gives attachment to 

 the Trapezius. 



Inner two-thirds. — This part may be described as having three borders and 

 three surfaces. The anterior border extends from the anterior border of the 

 outer one-third to the inner extremity of the bone, separating the anterior and 

 inferior surfaces. The superior border extends from the upper part of the pos- 

 terior border of the outer one- third to the inner extremity of the bone, separat- 

 um the anterior and posterior surfaces of the clavicle. The posterior border 

 extends from the conoid tubercle to the rhomboid impression, separating the 

 posterior and inferior surfaces. The anterior surface gives attachment to the 

 Pectoralis major and the Sterno-cleido-mastoid muscles. The posterior sur- 

 face gives attachment to the Sterno-hyoid and occasionally the Sterno-thyroid. 

 It has a nutrient foramen which is directed outward according to Rule 2, 

 Lesson ]. Sometimes there are two foramina, one of which may be mi the 

 inferior surface. The inferior or subclavian surface has near its inner part the 

 rhomboid impression which gives attachment to the costo-clavicular or rho- 

 boid ligament; this impression is about as inch long. The subclavian groove 

 occupies about the middle' one-third of the under surface of the clavicle and 

 gives attachment to the Subclavius muscle. The sternal extremity is triangu- 

 lar, with one angle above and two below; it looks inward, downward and a 

 little forward. It is convex from above down and concave antero-posterior- 

 ily. It articulates with the manubrium and its circumference is rough for the 

 attachment of the ligaments of this joint. The acromial extremity has an oval 

 articular facet somewhat convex, which is directed downward and forward to 

 articulate with the acromion; its circumference is rough for the attachment of 

 the ligaments of this joint. The righl clavicle is longer, thicker, and rougher 

 than the left. Those of the male are longer, thicker, rougher ami more curved 

 than those of the female. 



