The Sternum 127 



THE STERNUM. 



The sternum (Fig. 58) consists of a linear series of six segments, 

 the sternebrae The first segment is the manubrium sterni. 

 It is about twice the length of the middle segments. It is some- 

 what triangular in section, two of its surfaces being ventrolateral, 

 the third dorsal and directed toward the thoracic cavity. To its 

 anterior tip is attached the sternoclavicular ligament, by which 

 the greatly reduced clavicle is united with the sternum 



The four middle segments are similar in appearance, and form 

 the body (corpus sterni). The sixth segment, described as the 

 xiphoid process (processus xiphoideus), is an elongated strip of 

 bone, to the posterior end of which is attached a broad, thin plate 

 of cartilage. 



The first costal articulation is situated at about the middle of 

 the manubrium, the remaining six at the points of junction of the 

 segments. Five of them occur singly, while the sixth and seventh 

 costal cartilages are attached together at the point of junction of 

 the last segment of the corpus sterni with the xiphoid process. 



THE SKELETON OF THE HEAD. 



The head-skeleton comprises : (i) the series of elements constitut- 

 ing the skull; and (2) the hyoid bone, with its connections. The 

 skull, or cranium — using that term in a general sense— includes the 

 cranium proper, that portion enclosing the brain and containing 

 in its wall the auditory capsules, and the bones of the face (ossa 

 faciei), the latter including the series of elements related for the 

 most part to the jaws and palate. The primary relations of the 

 constituents of the head-skeleton have already been indicated 

 above (p. 53). 



A. THE SKULL AS A WHOLE. 



The skull (Figs. 59-63) is a composite structure, consisting of a 

 larg6 number of elements, which, with the exception of the mandi- 

 ble, are united by synarthroses, so that they produce the effect of a 

 continuous mass. The mandible is a more or less independent 



