426 DISSECTION OF THE PIGEON. 



line is a prominent ridge, formed by the ventral 

 border of the carina, or keel of the sternum. 



Posteriorly the trunk ends in a short blunt tail. 



B. The Limbs. 



1. The wing. 



Identify the several hones of the wing hy feeling them 

 through the shin. Note also the varying positions of the sur- 

 faces of the several divisions of the wing, when it is extended 

 and folded respectively (p. 417). 



The ala spuria, or bastard wing, is a small tuft 

 of feathers attached to the phalanx of the preaxial 

 digit. 



2. The leg. 



The toes and the tarso-metatarsal region are, ex- 

 cept in some domesticated breeds, devoid of feathers 

 and covered with large horny epidermal scales. The 

 ends of the toes are provided with horny claws. 



C. The feathers. 



The possession of feathers, which are specially modified 

 epidermal structures, is one of the most characteristic features 

 of the bird. 



1. Stractore of a feather. 



Pull oxit one of the large feathers from the wing or tail ; 

 and note in it the following points. 



a. The scapus, or stem, is a stiff axial rod, running 

 the whole length of the feather. It consists of 

 two dissimilar portions, 

 i. The calamus, or quill, is the tubular semi- 

 transparent proximal portion, the base of 

 which is inserted in the skin. At the 

 proximal end of the quill there is a small 

 aperture, the inferior umbilicus ; and at its 

 distal end, between the quill and the vane, 

 there is a second aperture, the superior 

 umbilicus. 



