AMERICAN WARBLERS. ,59 



skull together of both are of the same length ( 1.14), but the Yellow has the bill 

 narrower with the upper mandible less curved ( see Fig. 34, D, Yellow; c, Chest- 

 nut-sided ) and the skull, measured across the base, .05 less. This difTerence in 

 the form of the skulls gives a corresponding difference in the form of the brains. 

 Thus while the cerebellum remains about the same size in both species ( see Fig. 

 33, A II, Yellow : B it. Chestnut-sided ), the cerebrum of the Yellow is small- 

 er (see Fig. 33 A i and B i ), as are also the optic lobes ( see Fig. 33, A' v and 

 B" V, both cuts of lower side of brain ), but the medulla oblongata is about the 

 same size in both ( see Fig. 33, A" \\ and B' vi ). 



The cervical vertebrae in both warblers are ten, but in the Yellow each is 

 narrow and long, so that the entire neck is .10 longer than in the Chestnut-sided. 

 The length of the back in both is about 1.16, measured to the oil sack, but this 

 is larger in the Yellow^ (see Fig. 35, A Ji, Yellow : B i. Chestnut-sided ). 



Fig. 34. 



^-fc 



-^l 



V, viscera of Yellow Warbler ; B, same of Chestnut-sided : V, syrinx; H, Heart; L, right, R, left lobes 

 of liver; S, Stomach; I, Intestine; D, Duodenum ; T, Vent. C, Upper mandible of Yellow Warbler ; D, 

 same of Chestnut-sided. 



Beneath both have the bodies of exactly the same width, and the keel of the 

 sternum is of the same length ( see Fig. 35, A, Yellow ; B, Chestnut-sided ; k, 

 keel in both ), but in the Yellow the abdomen is longer, measured from the pos- 

 terior end of the keel to the vent ( see Fig. 35, A ). 



In the wing bones, the humerus and the hand of both are of the same length, 

 but the forearm of the Yellow is shorter by .04. The second primary of both is 

 the longest, and both hvae nine secondaries. 



The tails are of ipiite different proportions, that of the Yellow being .25 

 .shorter than that of the Chestnut-sided, yet its under coverts are .22 longer ( see 

 Fig. 33, 1, Yellow ; 2, Chestnut-sided ), but there is less difference in the upper 

 co.verts. 



