524 MAMMALIAN ANATOMY 



The cephalic surface is flattened ; it is narrower at the medial end 

 than at the lateral end. 



The caudal surface is more rounded, and is often marked near the 

 medial end by a crest along the ventral border. 



The medial end of the bone frequently has a distinct caudal 

 direction. 



Nomenclature. Clavicle is from clavicula, |the diminutive of 

 clavis, a key. Hyrtl 1 regards it as probable that clavis was also the 

 name of a curved door-latch and with this meaning was applied to 

 the collar-bone. Clavis is derived from the Greek cleis, cleidos, a key, 

 whence cleido-mastoid for one of the clavicular muscles. The German 

 word is das Schlusselbein, the French, la clavicule. 



Determination. When the concave dorsal border is held upper- 

 most and the curved end away from the student, the more rounded 

 caudal surface and the inclination of the medial end will be on the 

 side to which the bone belongs. 



Muscular Attachments. The cephalo-humeral muscle covers 

 the clavicle and is firmly attached to its ventral aspect in the lateral 

 half. The cleido-mastoid muscle is attached in the medial half. 



Ossification. The clavicle is said to be developed in membrane 

 from a single centre of ossification. 



HUMAN CLAVICLE. 



The clavicle in man is a relatively larger and much more impor- 

 tant bone than it is in the cat. It articulates by movable joints with 

 the acromion of the scapula and with the manubrium of the sternum, 

 and hence attaches the upper limb to the skeleton of the trunk. By 

 holding the shoulder-joint out from the body, while permitting free- 

 dom of motion, it enables the limb to accomplish most effectively a 

 greater variety of movements. 



When viewed from above or below, the clavicle has a sinuous 

 curve ; its medial two-thirds are bowed forward (ventrally) and its 

 lateral third is bowed backward (dorsally). When viewed from in 

 front or behind, its long axis is almost straight. For convenience 

 of description the clavicle is divided into an outer (lateral) third 

 and an inner (medial) two-thirds (Fig. 416). 



The outer third is strongly compressed from above downward and 



1 Onomatologia Anatomica. 



