82 SPECIAL ANATOMY. 



Figure : cylindrical, sigmoidal, at the internal extremity thick 

 and round, external flat. 



Curvatures : convex, anteriorly, in the sternal, posteriorly, in 

 the acromial half. 



Connection: with the breast bone, the shoulder-blade, and 

 often, with the first rib. 



a. Body, middle piece, almost immediately under the skin, is frequently 

 fractured, with Tubcrculum for m. Cleido-mastoid. Inferior surface, exter- 

 nally broad, with a rough line, for m. Siibclavius ; with an articular surface 

 internally, for the first rib ; in the middle third corresponding to the first in- 

 tsrcostal space, for Plex. brachialis et Vasa axillaria; the outer third, united 

 with Proc. coracoid. by the I/gam. Conoid, et Trapezoid. Posterior border, 

 two-thirds concave, one-third convex, externally. Lies on Subclavian vein ; 

 behind that Art. et Plexus brachialis. 



b. External termination, extremitas acromialis, for m. trapezius et deltoideus, 

 flat, weak, and easily broken ; with an articular surface for Acromion. 



c. Internal termination, extremitas slernalis, enlarged, angular, covered with 

 cartilage, projects over the articular surface of the Manubrium sterni into the 

 incisura clavicularis of which, it is received ; for m. sterno-cleido-mastoid., and 

 pectoralis major. 



Varieties. In the female the Clavicle is more slender, less curved, and 

 more horizontal. Structure: The medullary canal in the interior of the 

 Clavicle is very small ; the extremities consist of more Spongy f tissue. 



Development, at a very early period, at the thirtieth to the 

 thirty-fifth day from one osseous nucleus in the centre. In the 

 fifteenth to the eighteenth year an osseous nucleus appears as a 

 thin disc at the sternal end. In mature childhood the humerus 

 is only about |, in adults larger than the clavicle. 



The shoulder is placed before and behind close to the Thorax, 

 but stands out from it, and the space thereby formed forms the 

 superior part of the cavity of the axilla. 



96. II. Os humeri s. brachii, Bone of the upper arm. 



Position : between shoulder and fore-arm, on the sides of the 

 chest. 



Length : reaching downwards to the second Lumbar vertebra, 

 farther in Negroes. 



Direction: parallel with the axis of the trunk, yet rather 

 oblique from above downwards, and without inwards. 



Figure : tubular, cylindrical. 



Connection : with the shoulder-blade and the fore-arm. 



a. Superior extremity with: 1. Caput humeri, a segment of a sphere, 

 about ; lies in the Cavit. glenoid. scapulae, is surrounded by a circular flat 

 groove, the Collurn humeri of Anatomists, and forms an obtuse angle with 



