16 THE STRUCTURE AND LIFE OF BIRDS cnap, 
The Ribs. 
The ribs have very remarkable cross-pieces, called 
Uncinate—ze., 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— 
eg., 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 
the 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, 
