ANATOiMY OF TtlE HORSE. 11 



side : occasionally there exist ihirty-eigbt, and even forty ribs. 

 They are distinguished by their numerical order, counting from 

 before backwards. 



Co)iJ'ormation. In general similar : they are elongated, curv- 

 ed or twisted, convex along their outer sides, concave along 

 their inner, and taking a direction from within outwards and 

 from above downwards; they vary however in their length, de- 

 gree of curvature, and obliquity of direction. 



Division. Into true or sternal ribs, and false or asternal ; the 

 former, nine in number, being those whose cartilages are actu- 

 ally inserted into the sternum ; the latter, the remaining nine, 

 being only connected therewith through the intervention of 

 others. Each rib possesses two extremities, two surfaces, and 

 two borders. 



Extremities. The superior or vertebral, comprehends — 1. The 

 head, the protuberant or antero-superior portion, presenting 

 two convex smooth surfaces, for articulation with the bodies of 

 the vertebree between which it is received, and these divided by 

 a rugged notch, into which is fixed the interarticular ligament 

 of the head, 2. The neck, the contracted part, supporting the 

 head. 3. The tubercle, the prominence behind the head, at the 

 root of the meek, which has a flat smooth surface for articu- 

 lation witii the transverse process of the hinder vertebra con- 

 nected with the head. 4. In front of the tubercle, running 

 across the back of the neck, is a groove, along which make their 

 exit branches from the intercostal vessels and nerves. The in- 

 ferior or sternal extremity swells a little in volume, and is of 

 less compact or more porous texture than the bone above: it is 

 terminated by an oval roughened depression ; from this takes 

 root the cartilage of the nb, which thence proceeds at an angle 

 more or less obtuse and rounded to the sternum. 



Surfaces. The external is convex and more or less uneven. 

 The ribs do not form regular arches ; they project outwards 

 from the spine, and then curve suddenly downwards, the poste- 

 rior ones at the same time inclining backwards : the place where 

 the rib commences its descent, the most curved or crooked part, 

 is named its angle. In all the long ribs this surface, anteriorly, 

 is more or less grooved for the attachment of the external inter- 

 costal muscles. — The internal surface is uniformly concave, 

 smooth, and polished. It is lined by the pleura. 



Borders. With the exception of the first and last ribs, the 

 anterior borders are thin and sharp ; the posterior, obtuse and 

 rounded : the former give attachment to the intercostal mus- 

 cles ; the latter, along the upper half however only, present 

 grooves in which run the intercostal vessels and nerves. 



