l8o VERTEBRATES 



on the inside? How does the feather grow? Where does 

 it get its nourishment? Does it have any direct communi- 

 cation with the blood in the body? What causes the dif- 

 ference in plumage in the different birds? Does the pin- 

 feather explain this? Returning to the original feather 

 now can you find any trace of the old pinfeather capsule 

 upon it? When do you think a feather stops growing? 



e. How many different kinds of feathers do you find? 

 Those from the last segment of the wing are primary quills, 

 those on the next to the last segment are the secondary 

 quills, those at the tail are the rectrices, those covering the 

 bases of the quills are the coverts, and the remainder are 

 the contour feathers. Get one of each, put them in a group 

 and study their differences. 



f. Make a list of the various kinds of covering found on 

 the bird. 



Internal Structure. — I. The Body Wall.— (i) Ob- 

 serve the ridge on the ventral side and follow it backward 

 and forward to its limit. With the scalpel cut through the 

 skin on the right of this ridge and sever the flesh from the 

 hard portion. This bone is called the keel, or sternum. 

 Note its shape. Cut the flesh backward to the end of the 

 bone and pull it outward. This exposes two muscles. What 

 is their shape ? What are their relative sizes ? One is called 

 pectoralis major and the other, pectoralis minor. Can you 

 tell to which muscle each name belongs ? How are the mus- 

 cles attached to the keel bone ? Follow them up to the wing 

 and find how they are attached to the wing bone. Where 

 the muscle ends in a whitish tissue is it a part of the muscle 

 or something added to the muscle ? This whitish substance 

 is called a. tendon. What seems to be its origin ? 



