126 ANATOMY OF THE RABBIT. 
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 
eLc. the ribs and the sternum with the 
C.C. ie assistance of the thoracic vertebra. 
eae It encloses a large space, the 
es thoracic cavity (cavum thoracis). 
+h The latter is conical in shape, with 
ARK Aan the apex directed forward. The 

TS. hy dorsoventral diameter of the cavity 
é RR, E is considerably greater than the 
| ees transverse diameter. Apart from 
IIS the intercostal spaces, the cavity 
rN 2 is open at two points: anteriorly, 
Ce: y\% S the first thoracic vertebra, the first 
aa On 4: rib, and the manubrium_ sterni 
PNT, ‘ together enclose a small opening, 
3 the superior thoracic aperture 
6 (apertura thoracis superior); pos- 
> z teriorly, the seventh and succeed- 
ing ribs, together with the posterior 
thoracic vertebrae and the xiphoid 
process of the sternum, enclose a 
Fic. 58. The sternum and first rib, much larger DENNIS the inferior 
ventral view: 1-7, the true ribs; 8, frst thoracic aperture (apertura thor- 
false rib; c.c., head of rib; cl.c., neck of eee : 
rib; cr., costal cartilage; cr.c., body of rib; acis inferior). In the natural con- 
c.s., body of sternum; m.s., manubrium 
sterni; 0.c.,bone-rib; p.x.,xiphoid process; dition it is largely closed by the 
t.c., costal tubercle. E 
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. 


