OSTEOLOGY AND ARTHROLOGY 19 



inferior and posterior part of the thorax, and which forms 

 the lateral limits of the epigastric region. In the dog and cat 

 the ribs are thick and almost cylindrical ; the costal car- 

 tilages are thicker at the margin of the sternum than at their 

 costal extremity. In the ox, the ribs are flattened laterally 

 and are very broad, the more so as we examine a portion 

 further from the vertebral column. From the second to the 

 twelfth they are quadrangular in the superior fourth, and 

 thicker than in the rest of their extent. The first costal 

 cartilage is vertical ; the following ones are progressively 

 more oblique in a direction downwards and forwards. The 

 four or five cartilages which succeed the first unite with slight 

 obliquity to the sternum ; their union with that bone gives 

 the impression of a very strong, well-knit apparatus. The 

 costal cartilages which unite with the sternum are flattened 

 laterally in the portions next the ribs, and flattened from 

 front to back in the rest of their extent. 



In the horse the ribs increase in length from the first to the 

 ninth ; they are flattened from without inwards, and increase 

 in width from the first to the sixth or seventh, and the fol- 

 lowing ones become narrower. The costal cartilages, from 

 the second to the eighth, are, as in the ox, at first flattened 

 laterally, near the ribs ; while near the sternum they are 

 flattened from front to back. 



In birds, the ribs are each furnished with a flat process 

 (Fig. 18, 10), which springs from the posterior border, is 

 directed backwards, and overlaps the external surface of 

 the succeeding rib. These processes are not found, as a rule, 

 on the first or last ribs 



As for the costal cartilages, they are, as a rule, ossified, 

 and receive the name of inferior ribs (Fig. 18, 11), united to 

 the preceding (superior ribs ; Fig. 18, 9) by articulation ; 

 by the other extremity they are joined to the sternum ; the 

 first superior ribs generally want them. Sometimes the last 

 inferior rib becomes connected with the one that precedes it, 

 not articulating with the sternum ; and thus recalls the 

 relations of the asternal ribs which we have noticed in our 

 study of the mammals. 



In the bat, as in birds, the costal cartilages are ossified. 



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