10 THE STRUCTURE OF THE FOWL 



are bonily united in order that a firm founda- 

 tion may be established for the wing. But the 

 most extensive fusion occurs in the lumbar 

 and sacral regions. Here, moreover, the hip- 

 bone, throughout the greater part of its length, 

 is immovably fixed to the vertebral column 

 by a bony union. 



Each vertebra consists of a rod-like body, 

 surmounted by a vertebral arch ; these circum- 

 scribing a vertebral foramen which forms part 

 of the vertebral canal of the articulated skeleton. 

 The ends of the body of a vertebra have 

 saddle-shaped surfaces for articulation with 

 adjacent vertebrae. The cranial surface is 

 concave from side to side and convex in a 

 dorso-ventral direction. The caudal surface, 

 naturally, has its curves disposed in the reverse 

 direction. In many vertebrae the ventral 

 aspect of the body carries a median, flattened 

 process. In a typical vertebra the arch is 

 produced dorsally into a spinous process, and 

 carries two cranial and two caudal articular 

 ^processes with smooth surfaces for contact 

 with similar processes on neighbouring bones. 

 From each side of a vertebra projects a trans- 

 verse process attaining a considerable length 

 in the thoracic, lumbar, and sacral regions. 



