16 THE STRUCTURE AND LIFE OF BIRDS chap. 



The Ribs. 



The ribs have very remarkable cross-pieces, called 

 Uncinate — i.e., hooked — processes (UP, fig. 2) that 

 spring from about the middle of their upper part and 

 slope backwards and upwards. These uncinate pro- 

 cesses, no doubt, serve to strengthen the chest, and, 

 apart from this, they possess a singular interest. 

 They are common to all birds, but absent in nearly 

 all reptiles. In a very few lizards they are found — 

 e.g., in the Hatteria, a native of some of the islands of 

 the New Zealand group, and now so rare that it may 

 be in danger of extermination (fig. 1). It will be seen 

 that each rib has a joint at a point considerably 

 nearer to the sternum than to the backbone, the two 

 parts being spoken of as the dorsal ribs (Latin 

 dorsum, the back) and the sternal pieces respectively. 



The Hind Limb. 



In naming the bones of the leg, the genius of the 

 older anatomists for seeing resemblances where it is 

 difficult for us to see any has run riot. The larger of 

 trie two leg bones is the Tibia or flute, the smaller one 

 is the Fibula or brooch (F, fig. 1, 3). The Acetabulum, 

 as they called the socket of the thigh-bone, is a happier 

 name. Strictly the word means a vinegar-pot, and 

 it is used of any cup-shaped vessel. A bird's Ace- 

 tabulum (A, fig. 8) is remarkable. If you look at a 

 skeleton in a museum you will see that the cup has no 

 bottom to it. The bottom was formed of membrane, 



