362 SKELETON OF THE FOWL 



Of these two, the first is small, but has distinct 

 capitular and tubercular articulations : the second 

 is larger, and bears on its posterior border a back- 

 wardly projecting uncinate process, which over- 

 laps the next rib. 



b. \ The thoracic ribs are Jive on each side, and slightly 

 increase in size from before backwards : each 

 consists of vertebral and sternal portions, meeting 

 at an angle. 



1. The vertebral portions are flattened and slightly 

 curved bars of bone, which articulate by capi- 

 tular and tubercular surfaces with the centra 

 and transverse processes of their respective 

 vertebrae. Uncinate processes project back- 

 wards from the posterior borders of all, except 

 the last, or sometimes the last two. 

 ii. The sternal portions are slender, nearly straight 

 rods of bone, which run forwards and down- 

 wards, from their j unctions with the vertebral 

 portions, to the side of the anterior part of 

 the sternum, with which they articulate. 



2. TJiP ^tfirTmnij or breastbone, is very large, and projects 

 back far beyond the ribs, and over the greater part 

 of the wall of the abdomen. Its ventral surface is 

 raised into a prominent vertical crest or keel, which 

 gives origin to the muscles of flight. 



i. The body of the sternum is a somewhat spoon- 

 shaped plate of bone : it is wide and stout in 

 front, and perforated on its concave dorsal 

 surface by apertures, through which the air- 

 sacs communicate with the cavity of the bone : 

 it is narrow in the middle portion of its length, 

 but widens somewhat behind. 

 ii. The pmnubrmm is a small vertical plate of bone, 

 projecting from the anterior end and ventral 

 surface of the body. 



iii. The carina, or keel r is a very prominent triangular 



