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: (1) 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 
large number of elements, which, with the exception of the mandi- 
ble, are united. by synarthroses, so that they produce the effect ofa 
continuous mass. The mandible is a more or less independent 
