THE RIBS. 



35 



oblong, mostly constricted in the centre, and expanded wher© 

 they articulate with one another: the four or five anterior one3 

 are slightly flattened above, hollowed longitudinally below, and 

 they possess generally incomplete arches and imperfectly-developed 

 processes. The remaining segments consist merely of centra, 

 which diminish in size posteriorly. There is, therefore, no complete 

 neural canal in the caudal region, only the first two or three 

 vertebrae being sometimes found with their neural arches complete. 



THE THOBAX. 



The dorsal vertebra superiorly, the ribs and their cartilages 

 laterally, and the sternum or breast-bone inferiorly, form the 

 skeleton of a large cavity called the Thorax. 



THE EIBS. 

 (PL. I. T. T.) 



In the horse the ribs usually number eighteen on each side. 

 They extend in a series of arches of varying curvature from the 

 dorsal vertebra above, towards the sternum and sides of the 

 abdomen below. Their shape, in a great measure, determines 

 the conformation of the thorax ; they protect its contents, and 

 materially aid in its contraction and expansion. 



To the distal end of each rib an elongated piece of cartilage is 

 attached, and eight of these connect the eight anterior, termed 

 sternal or true ribs, with the sternum ; the ten posterior ribs. 

 having only an indirect sternal attachment are known as asternal 

 or false ribs. The ribs pass first outwards and backwards, and 

 then in an arched direction downwards, their cartilages inclining 

 inwards and forwards. They gradually lengthen from the first to 

 the ninth, after which they progressively shorten ; their curvature 

 increases from the first, which is nearly straight, to the last, which 

 forms a large segment of a comparatively small circle. The 

 greatest breadth is attained in the fifth, sixth, seventh, and eighth, 

 which, in their middle portions, exhibit the more especial characters 

 of flat bones. 



Each rib presents for consideration superior and inferior 

 extremities, and a shaft or body having anterior and posterior 

 borders and external and internal surfaces. 



D 



