30 THE STRUCTURE OF THE FOWL 



(c) Pes. 



a. Tarsus. 



^. Metatarsus. 



7. Digits. 

 The term " girdle " when apphed to the 

 hip-bone of the fowl is a misnomer, inasmuch 

 as, instead of the bones of opposite sides of 

 the body meeting and uniting at a symphysis 

 in the mid-ventral line of the body, they are 

 most widely separated at this place. This 

 arrangement is associated with the laying of 

 relatively large eggs. Were the bony bound- 

 aries of the pelvis — the cavity within the hip- 

 bones — complete, as they are in mammals, 

 passage of the egg would be impossible unless 

 the pelvis were of a relatively enormous size. 

 In the existing condition the soft and yielding 

 ventral wall of the cavity is adapted to the 

 passage of an egg of considerable dimensions. 

 The extensive fusion of the hip-bone with the 

 vertebral column compensates the weakness 

 which would otherwise result from the absence 

 of a symphysis. 



The hip-bone of birds (Fig. 7) resembles that 

 of mammals in being composed of three elements 

 — ilium, ischium, and pubis — meeting at the 

 deep concavity — the acetabulum — into which 



