OSTEOLOGY. 



65 



tlie inner surface of tlie cartilage of elongation, are attached 

 the rliomboidei muscles. 



HUMERUS is a long round bone, wliicli is situated 

 below the scapula, running obliquely from above down- 

 wards and backwards, forming with the scapula an obtuse 

 angle posteriorly. It is a very stout bone, and its superior 

 extremity is much larger than its inferior. The superior 

 extremity presents a head and four tubercles. The latter 

 form a continuous chain occupying the anterior part of 

 this extremity. The head is situated at the posterior part 

 and is convex. Since it looks directly upwards in the 

 natural position of the bone it seems to be inclined to the 

 posterior part. It extends slightly on to the fourth 

 tubercle, and between it and the other tubercles is a space 

 elongated from side to side with numerous large foramina ; 

 this is occupied by fat in the fresh subject. On the inner 

 side of the upper extremity is a roughened process, broad 

 posteriorly, terminating in a point anteriorly in joining the 

 internal tubercle ; to this subscapularis is attached. The 

 three tubercles on the anterior part are termed respectively 

 external, middle, and internal. The internal tuhercle is the 

 smallest, receiving the termination of the roughened spot 

 just mentioned, posteriorly, and externally presents the 

 commencement of a synovial surface coated with fibro- 

 cartilage which dips down into the shallow fossa between 

 the internal and middle tubercles and then, after com- 

 pletely covering the middle tuhercle, dips into the deep fossa 

 between this and the external tubercle, terminating after 

 investing the inner surface of the latter. Over this sur- 

 face the tendon of flexor brachii plays ; hence it is lubricated 

 with synovia, and presents a large and important bursa, 

 which is separated from the capsular ligament of the 

 joint by the fat in the perforated space in front of the 

 head. Below this surface may be seen a series of small 

 articular foramina. Both the external and internal 

 tubercles afford attachment to antea spinatus and pectomlis 

 magnus which serve to bind flexor brachii in its situation, 

 but the external tubercle gives the most extensive attach- 

 ment and is continued inferiorly as a stout ridge much 

 roughened, especially above and below, superiorly for 

 attachment of one tendon of postea spinatus, inferiorly it 

 presents a tubercular termination roughened and curved 

 slightly backwards where teres externus is attached. Just 



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