126 



Anatomy of the Rabbit. 



cr.c. 



7n-s. 



c.s. 



in the last four, the tubercle bears a sharp, dorsally-directed process 

 for muscular attachment. The slender portion of the rib inter- 

 vening between the head and tubercle is the neck (collum costae), 

 the remaining larger portion being distinguished as the body of the 

 rib (corpus costae). 



The bony thorax is formed by 

 the ribs and the sternum with the 

 assistance of the thoracic vertebra. 

 It encloses a large space, the 

 thoracic cavity (cavum thoraciis). 

 The latter is conical in shape, with 

 the apex directed forward. The 

 dorsoventral diameter of the cavity 

 is considerably greater than the 

 transverse diameter. Apart from 

 the intercostal spaces, the cavity 

 is open at two points: anteriorly, 

 the first thoracic vertebra, the first 

 rib, and the manubrium sterni 

 together enclose a small opening, 

 the superior thoracic aperture 

 (apertura thoracis superior) ; pos- 

 teriorly, the seventh and succeed- 

 ing ribs, together with the posterior 

 thoracic vertebrae and the xiphoid 

 process of the sternum, enclose a 

 much larger opening, the inferior 

 thoracic aperture (apertura thor- 

 acis inferior). In the natural con- 

 dition it is largely closed by the 

 diaphragm. The curved boundary 

 formed by the ribs in this region is the costal arch (arcus costarum), 

 the angle formed at the point of attachment of the xiphoid process 

 being the infrasternal angle (angulus infrasternalis). 



Through their articulations with the vertebral column, and the 

 nature of the costal cartilages, the ribs are capable of being moved, 

 or rotated, forward. The movement results in an increase of the 

 extent of the thoracic cavity, and is of importance in respiration. 



Fig. 58. The sternum and first rib, 

 ventral view: 1-7, the true ribs; 8, first 

 false rib; c.c, head of rib; cl.c, neck of 

 rib; cr., costal cartilage; cr.c, body of rib; 

 c.s., body of sternum; m.s., manubrium 

 sterni; o.c, bone-rib; p.x., xiphoid process; 

 t.c, costal tubercle. 



