96 THE BONES. 



the shortness and thickness of its cartilage, and particularly by the articular facet 

 which this cartilas^e exhibits inwardly, to correspond to that of the opposite rib. 

 The last rib has no channel on its external surface, and the facet of its tuberosity 

 is confounded with the posterior facet of the head. This last character is also 

 nearly always remarked in the seventeenth rib, and sometimes even in the 

 sixteenth. 



In the Ass, the ribs in general, but particularly those most posterior, are less 

 curved than in the Horse. They differ more particularly in the curve of the neck 

 being much shorter — a difference which is most obvious when the goniometer is 

 applied to the angle of the rib, and the most salient part of the head and tube- 

 rosity. By this means we have obtained an angle the value of which was greater 

 in the Ass than in the Horse : from 7><° to 130° for the external ribs, and from 

 100° to 132° for the asternal ribs, of the first ; from 60° to 125° for the sternal, 

 and from 140° to 150° for the asternals, of the second. The upper extremity of 

 the sternal ribs in the Ass is less twisted outwards than the same part in the 

 Horse ; and in the latter, the plane which passes by the head of the rib is more 

 distant than the plane which, in the Ass, passes across the tubercle. 



The ribs of the Mule are intermediate between those of the Ass and Horse, 

 with regard to the value of the angle just indicated ; they approach those of the 

 Ass by the twist in their superior extremity. 



Differential Characters in the Ribs of other Animals. 

 The number of rib:^ varies like that of tlie dorsal vertebrae. The following table'* indicate 

 the number uf these bones in the different domesticated animals : — 



Pig 14 



Ox l.S 



Sheep 13 



Goat 13 



Dog 13 



Camel ... 12 



Rabbit 12 



A. Ruminants. — These animals, with the exception of the Camel, have eight sternal and 

 five asternal ribs. 



In the Ox, they are longer, wider, and less arched than in Solipeds. The articular 

 eminences of the superior t-xtremity are voluminous and well <letafhed; the neck especially is 

 very long. The sternal ribs are joined to their cartilage of prolnngment by a real diarthrodiai 

 articulation. In the last rib, and sometimes in tlie one before it, the tuberosity is scarcely 

 perceptible, and has no articuhir facet. In the Sheep and Goat, the sternal ribs are consolidated 

 with the cartilages (Figs. 6. 7). 



The Camel has eight sternal and four asternal ribs. The rib.s increase in length to the 

 tenth, and in width to the si.xth only. They are less curved and are shorter, proportionately, 

 tiian those of the Ox, the shortness being very marked in the first three. The tubercle is less 

 de'achefl than in the Ox, but the neck is longer and stronger (Fig. 8). 



B. Pig. — In this animal there are fourteen pairs of ribs, seven of which are sternal and 

 seven asternal. The first are provided with cartilages of prolongment flattened on both sides, 

 extremely wide and sharp, and convex on their superior border. In the four last asternal ribs, 

 the fitcet of their tuberosity is confoundi'd with the posterior facet of the head (Fig. 3). 



C. Carnivora. — They possess thirteen ribs on each side — nine sternal an.l four asternal. 

 These are very much arched, narrow, and thick, and their cartilages rarely ossify. In the Dog, 

 the articular facet of tiie tuberosity remains isolated from the posterior facet of the head in all 

 the ribs. It is absent in the three last ribs of the Cat (Fig. 2). 



The Thorax in General. 



The description of the interior of the thoracic cavity will be referred to when 

 treating of the respiratory apparatus. It is only necessary here to examine the 



