166 ANATOMY OF THE RABBIT 



As a result of their articulations with the vertebral column, 

 and of the flexible nature of the costal cartilages, the ribs are 

 capable of being moved, or rotated, forward. The movement 

 brings about an increase of the extent of the thoracic cavity, and 

 is of importance in breathing. 



THE STERNUM 



The sternum (Fig. 84) consists of a linear series of six segments, 

 the sternebrae. The first segment is the manubrium sterni. It is 

 about twdce the length of the middle segments. It is somewhat 

 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 connected 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 with a broad, thin plate of cartilage attached to its posterior 

 end. 



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 consti- 

 tuting 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 contain- 

 ing 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). 



The Skull as a Whole 



The skull (Figs. 85-88) is a composite structure, consisting of 

 a large number of elements, which, with the exception of the man- 



