242 Observations id show 



That ribs are not essential to the breathing of all animals 

 whose lungs are situated in the same manner as in snakes, 

 is proved by the syren having no ribs ; but as this animal 

 has also gills, and can breathe in water as well as in air, 

 the lungs are not so constantly employed, and probably a 

 less perfect supply of air to them may suffice. 



In animals in general, the ribs are articulated to the back 

 bone by means of a convex surface, which moves upon a 

 slightly concave one formed upon two of the vertebraj, 

 partly on the one and partly on the other, so that there is 

 a rib situated between every two vertebrae of the back ; but 

 in the snake tribe, the head of the rib has two slightly con- 

 cave surfaces which move upon a convex protuberance be- 

 longing to each vertebra, so that there is a rib to each of 

 the vertebrae. 



One advantage of this peculiarity is, that it prevents the 

 ribs from interfering with the motion of the vertebrae on 

 one another. The vertebrae are articulated together bv ball 

 and socket joints (the ball being formed upon the lower 

 end, and the socket on the upper one), and have therefore 

 much more extensive motion than in other animals. 



The muscles, which bring the ribs forward, consist of 

 five sets, one from the transverse process of each vertebra 

 to the rib immediately behind it, which rib is attached to 

 the next vertebra. The next set goes from the rib a little 

 way from the spine just beyond where the former termi- 

 nates; it passes over two ribs, sending a slip to each, and is 

 inserted into the third: there is a slip also connecting it 

 with the next muscle in succession. Under this is the third 

 set, which arises from the posterior side of each rib, passes 

 over two ribs, sending a lateral slip to the next muscle, and 

 is inserted into the third rib behind it. 



The fourth set passes from one rib over the next, and is 

 inserted into the second rib. 



The fifth set ooes from rib to rib. 



On the inside of the chest there is a strong set of muscles 

 attached to the anterior surface of the vertebrce, and passing 

 obliquely forwards over four ribs to be inserted into ihc 

 fifth rib, nearly at the middle part between the two ex- 

 tremities. 



From this part of each rib a strong flat muscle comes 

 forward on each side over the viscera, forming the abdo- 

 minal muscles, and uniting in a beautiiul middle tendon, 

 so that the lower half of each rib, wliich is beyond the 

 origin of ibis muscle, and wliich ts only lateraUv connected 

 to it by loose cellular mcn)bi;ii)c, is external to the belly of 



the 



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