408 SKELETON OF THE FOWL. 



articulated, the remainder being fused with 

 the transverse processes of the corresponding 

 vertebrae. 



Of these two, the first is small, but has dis- 

 tinct capitular and tubercular articulations ; the 

 second is larger and bears on its posterior border 

 a backwardly projecting uncinate process, which 

 overlaps the next rib. 

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

 increase in size from before backwards : each 

 consists of vertebral and sternal portions, meet- 

 ing at an angle, 

 i. The vertebral portions are flattened and slightly 

 curved bars of bone, which articulate by 

 capitular and tubercular surfaces with the 

 centra and transverse processes of their re- 

 spective vertebrae. Uncinate processes pro- 

 ject backwards 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 junctions with the vertebral 

 portions, to the side of the anterior part of 

 the sternum, with which they articulate. 

 2. The sternum, 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 moving the wings. 

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

 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 manubrium is a small vertical plate of 



