94 



THE BONES. 



2. The Ribs (Pleuropophyses) (Fig. 57). 



As has been already remarked, on each side of the thorax there are eighteen 

 ribs. These are nearly parallel to each other, and separated by the intervals 

 termed the intercostal spaces. Attached by their superior extremity to the 

 vertebrse of the dorsal region, these bones terminate at their inferior extremity 

 by an elastic and flexible prolongation, named the costal cartilage, by means of 

 which they are brought into direct or indirect relations with the sternum. The 



characters common to all the 

 ^'S- ^^- ribs will be first noticed, then 



the special features which serve 

 to distinguish them from each 

 other, and, lastly, the differences 

 they exhibit in other than Soh- 

 ped animals. 



A. Characters common to 

 ALL THE Ribs. — These will be 

 studied from a typical point of 

 view, first in the rib itseK, and 

 then in its cartilage. 



1. Description of a typical 

 rib. — A rib is an elongated 

 asymmetrical bone, oblique from 

 above to below, and from before 

 to behind, flattened on both 

 sides, curved hke a bow, and 

 twisted on itself in such a fashion 

 that its two extremities cannot 

 rest on the same horizontal 

 plane. It is divided into a 

 middle portion or bod//, and tivo 

 extremities. 



3Iiddle portion. — This offers 

 two faces and two borders. The 

 external face is convex, and 

 hollowed by a wide groove in 

 its anterior half ; it shows 

 superiorly, towards the point 

 corresponding to the angle of 

 the rib in Man, some tubercles 

 and muscular imprints. The 

 internal face is concave and 

 smooth, and covered by the 

 pleura, which separates it from 

 the lungs. The anterior border 

 is concave, thin, and sharp ; the posterior — convex, thick, and covered with rugged 

 eminences — is channeled iuAvardly by a vasculo-nervous groove, which disappears 

 near the middle of the rib. 



Extremities. — The superior has two eminences— a head {capitidum) and a 

 tuberosity (tuberculum) — which serve for the support of the rib against the spine. 



TYPICAL RIBS OF THE HORSE. 



, Inner face of the fifth sternal rib. B, External face 

 of the first asternal rib. 1, Head of the rib; 2, its 

 fissure ; 3, neck ; 4, tuberosity ; 5, articular facet ; 

 6, scabrous fossa for the insertion of the interosseous 

 costo-transverse ligament ; 7, groove on the external 

 face ; 8, vasculo-nervous groove on the posterior border ; 

 9, prolonging cartilage ; 10, A, articular tuberosity 

 for union with the sternum. 



