218 VERTEBRATES. 



1. Horny sheaths covering the mandibles and claws. 



2. Epidermal scales (^scutellce) covering the tarsus and 

 toes. 



3. Feathers covering the remaining exposed portions 

 of the skin, and constituting the plumage. 



But there are hidden areas of the skin which are bare. 

 By separating the feathers, find one of these on the median 

 line of the breast, and another on either side of the base 

 of the neck. 



Examine the stout, thick beak. Such a beak "is well 

 adapted to eating grain, to breaking the husks and 

 hulling out seeds. Examine the claws. Are they sharp 

 enough to be of much service as defensive weapons ? Are 

 the feet strong enough to indicate that the claws are used 

 for defense ? 



Examine the scales of the tarsus and toes. Note that 

 they overlap regularly down the front and sides, and that 

 a posterior series forms a sharp ridge down the back of the 

 tarsus. A tarsus with regularly overlapping scales such 

 as these is said to be scutellate. 



Plumage. Examine the plumage. Pluck one of the 

 longest primaries from a wing, and examine it. Observe 

 a median shaft bordered on either side by a web (or vane). 

 Observe that the shaft is made up of two parts, a lower 

 transparent part, the quill (or calamus) ; and the opaque 

 part, the rhachis, which bears the vanes. Make a cross 

 section through the calamus, and another through the 

 rhachis. What is the shape in cross section of the 

 calamus ? Of the rhachis ? What is the condition of 

 the interior of the calamus ? Of the rhachis ? Hold- 

 ing the rhachis horizontally, look at the cut end. Com- 

 pare the position of the vanes in relation to the rhachis 

 with that of the wings of the bird in relation to the body. 

 Why should the vanes be attached to its upper side ? 



