; TIKU;A.\. 



iii their inferior moiety, and arc developed at a very early period by three 

 centres of ossification : a principal for the middle portion and inferior 

 extremity, uiid two complementary for the head and tubcrosity. 



J. />r.-iT//i//dM of n t//jii<-al costal cartUage. Tho costal cartilage very 

 evidently represents the inferior rib ill birds; it is a cylindrical piece, 

 slightly compressed at the sides, and round and smooth on its faces and 

 1 (orders. Uy its superior extremity, it is united to the rib it serv 

 lengthen, and forms with it an angle more or less obtuse, opening in front. 

 At its inferior extremity, it is terminated by an articular enlarge- 

 ment, or by a blunt point. In youth, the costal prolongations are entirely 

 eonipused of cartilaginous matter, but they are soon invaded by ossification ;- 

 so that in the adult animal they are already transformed into a spongy 

 substance, with large oreola) which remain during life surrounded by a thin 

 layer of cartilage. 



B. SPECIFIC CHABACTEBS OF THE RIBS. The ribs, like the vertebras of each 

 region of the spine, have received numerical designations of first, second, third, 

 ( i.-.. eiiinputing them from before to behind. (See Fig. 1.) Owing to the pre- 

 sence of an altogether essential characteristic, they are naturally divided into 

 t\\(i great categories: the sternal or true ribs, and the asternal or false r!l*. 

 The sti nml /-//IN, numbering eight (the first eight), have their cartilages 

 terminating inferiorly by an articular enlargement, which corresponds to one 

 of the lateral cavities of the sternum, and brings the true ribs into direct 

 contact with this portion of the skeleton. The asternal ribs, ten in numl>er, 



n each other the last on the seventeenth, this on the sixteenth, and so 

 on by the inferior extremity of their cartilage, which ends in a blunt point. 

 The cartilage of the first false rib is united somewhat closely to the last 

 sternal rib, and it is through the medium of this that all the asternal ribs lie 

 indirectly on the sternum. 



If, however, the ribs are considered altogether, with regard to the differen- 

 tial diameters presented by them in their length, width, and degree of 

 incurvation, it will bo noted: 1, That their length increases from the first 

 to the ninth, and from this diminishes progressively to the last: 2, That the 

 same progressive increase and decrease exists in the cartilages ; 3, That they 

 me gradually wider from the first to the sixth inclusive, and then con- 

 tract by degrees until the eighteenth is reached; 4, That the curve described 



.h is shorter and more marked as the rib is situated more behind. It 

 may be added that the channel on the external face is less conspicuous in 

 proportion as the rib is narrow. 



The first rib, considered individually, is always distinguished by the 

 al>>. nee of the groove on its outer surface, the vasculo-nervous fissure on its 



rior border, and the groove or notch intermediate to the two facets of 

 it> articular head. It is also recognised by the deep muscular imprints on 

 its external face, the shortness and thickness of its cartilage, and particularly 

 by the articular facet which this cartilage exhibits inwardly, to correspond 

 to that of the opposite rib. The last rib has no channel on its external 

 surface; the facet of its tuberosity is confounded with the posterior facet of 

 the luad. This last character is also nearly always remarked in the 

 seventeenth rib, and sometimes even in the sixteenth. 



In the A-n and Mule, all the ribs in general, but particularly those most 



rior, are less curved than in the Horse. (In the Horse, a nineteenth 

 pair of ribs is sometimes found, and this even with five, and at other times 

 with six lumbar vertebra* ; it happens that the nineteenth rib is funned by 

 the transverse process of the first lumbar vertebra, and at tim- - a ligament 



