OSTEOLOGY. 47 



The anterior concave surface supports the rectum and gives 

 attachment to levator ani muscle and anterior sacro-coccygeal 

 ligament. 



The posterior convex surface presents rudimentary, articular 

 processes and transverse grooves. 



The apex is rounded, occasionally bifid, or deviated to one 

 side, and affords attachment to the levator ani and sphincter 

 ani muscles. 



The muscular attachments are coecygei, gluteus maximus, 

 extensor coccygeus (occasionally present), levator and sphincter 

 ani. 



Its ossific centres are four one for each segment. 



THE UPPER EXTREMITY. 



The upper extremity consists of the arm, forearm, and 

 hand. It is attached to the trunk by the clavicle and contains 



FIG. 19. 



1, sternal extremity; 2, costal facet for first rib; 5, acromial extrem- 

 ity; 6, 6, deltoid muscle; 7, 7, trapezius muscle. 



the following bones: Clavicle, scapula, humerus, radius, ulna, 

 eight carpus, five metacarpus, and fourteen phalanges. 



THE CLAVICLE, or collar- or key- bone, is a long bone, curved 

 horizontally like the italic letter f f extending almost horizontally 

 between the sternum and acromial process of scapula. Its inner 

 two-thirds are cylindrical and convex in front, its outer third 

 flattened from above downward and concave in front. It con- 

 sists of a body, or shaft, and outer, or acromial, and inner, or 

 sternal extremities. 



The shaft presents in its outer third the following points : 



Superior surface, rough impression in front for deltoid mus- 

 cle, rough impression behind for trapezius ; 



Anterior border, occasionally deltoid tubercle about the 

 centre for attachment of deltoid; 



Inferior surface, conoid tubercle at the posterior border for 

 conoid ligament ; oblique line extending outward and forward 

 from this for attachment of trapczoid ligament. 



