THE SKELETON IN MAMMALIA. THE RIBS. 491 



In MARSUPIALS there are almost always thirteen pairs 

 of ribs, whose sternal portions are very imperfectly ossified. 

 Notoryctes has fourteen pairs of ribs, eight of which are float- 

 ing: the first rib is very stout, and is abruptly bent on itself 

 to join the sternum. It has no distinct sternal portion. All 

 the other ribs are slender. 



Of the EDENTATES the Sloths have very numerous ribs ; 

 twenty-four pairs occur in C/ioloepus, and half of these reach 

 the sternum. In the Armadillos there are only ten or twelve 

 pairs of ribs, but the sternal portions are very strongly ossified. 

 The first rib is remarkably broad and flat, and is not divisible 

 into vertebral and sternal portions. 



In the SIRENIA there are a very large number of ribs 

 noticeable for their great thickness and solidity, but not 

 more than three are attached to the sternum. 



CETACEA. In the Whalebone whales the ribs are remark- 

 able for their very loose connection both with the vertebral 

 column and with the sternum. The capitula are scarcely 

 developed, and the attachment of the tubercula to the trans- 

 verse processes is loose. The first rib is the only one connected 

 with the sternum. In the Toothed whales the anterior ribs 

 have capitula articulating with the centra, as well as tubercula 

 articulating with the transverse processes ; in the posterior 

 ones, however, only the tubercula remain. Seven pairs of 

 well-ossified sternal ribs generally meet the sternum. In the 

 Physeteridae most of the ribs are connected to the vertebrae 

 by both capitula and tubercula. 



In the UNGULATA the ribs are generally broad and flattened, 

 and this is especially the case in the genera Bos and Bubalus 

 (fig. 101, 6). The anterior ribs are short and nearly straight, 

 and sternal ribs are well developed. The Artiodactyla have 

 twelve to fifteen pairs of ribs, the Perissddactyla eighteen or 

 nineteen, and Procavia twenty to twenty-two. The Elephant 

 has nineteen to twenty-one pairs, seven of which may be float- 

 ing ribs. 



