96 THE BONES. 



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, 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 78° to 180° for the external ribs, and from 

 100° to 132° for the asternal ribs, of the first ; from 60° to 12r>° 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 riba varies like that of the dorsal vertebrae. The following table indicate 

 the number of these bones in the diflferent domesticated animals : — 



Pig 14 



Ox ; 13 



Sheep 13 



Goat 13 



Dog 13 



Camel 12 



Rabbit 12 



A. Rmninants. — These animals, with the exception of tlie 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 extremity are voluminous and well detached; the neck especially is 

 very long. The sternal ribs are joined to their cartilage of prolongraent by a real diarthrodial 

 articulation. In the last rib, and sometimes in the one before it, the tuberosity is scari'cly 

 perceptible, and has no articular 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 ribs increase in length to the 

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

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

 defachefl 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 prolongnicTit flattened on both sides, 

 extremely wifle and shar}), and convex on their superior bor.ler. In the four last asternal ribs, 

 the fncet of their tuberosity is confounded with the posterior facet of the head (Fig. 3). 



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

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

 the articular facet of the 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 



