164 ANATOMY OF THE RABBIT 



Caudal Region 

 The caudal or coccygeal vertebrae (vertebrae caudales, s. 

 coccygeae) are sixteen in number. They are segments of small 

 size, increasing slightly to the third, and then gradually decreasing 

 to the end of the column. As only the small tail muscles are 

 attached to them, they lack any marked projections. The arches 

 are complete in the first seven. The transverse processes are 

 vestigial in all except the third. At the end of the column, the seg- 

 ments are reduced to slender cylinders of bone representing the 

 vertebral bodies. 



THE RIBS 



The ribs (costae) are twelve in number on either side. Each 

 is composed of a dorsal portion, the costal bone (os costale), or 

 bone-rib, and a ventral portion, the costal cartilage (cartilage 

 costalis) (Fig. 84). From their attachment on the vertebral column 

 the bone-ribs are directed outward, downward, and backward. 

 The costal cartilages are directed for the most part inward, down- 

 ward, and forward. The first costal cartilage forms a pronounced 

 angle with the corresponding bone-rib. In the succeeding ribs the 

 angle is gradually replaced by a broad curve. 



Ribs are classified as true or sternal ribs (costae verae) and 

 false or asternal ribs (costae spuriae). The former — comprising 

 the anterior seven^ — are those directly attached to the sternum. 

 The latter — comprising the posterior five^ — are either indirectly 

 attached, or unattached. Those unattached are designated as 

 floating ribs. 



Generally speaking, the bone-ribs are cylindrical; but the 

 anterior five or six are more or less flattened, with their main sur- 

 faces respectively medial and lateral. The compression is most 

 marked in old animals. The first rib is extremely short. The 

 succeeding ribs increase in length to the sixth, and then decrease 

 to the twelfth. Each rib is curved, not uniformly but so that its 

 greatest convexity, or angle, is at some point toward the dorsal 

 surface. Passing backward, in succeeding ribs the point of greatest 

 convexity changes from a mediodorsal to a laterodorsal position. 

 This, together with the elongation of the more posterior ribs, 

 results in an enormous increase in the posterior extent of the 

 thoracic cavity. 



