Chap. Y. SUMMARY OF DIFFERENCES. 177 



presume that this may be safely attributed to disuse or lessened 

 exercise. The wings, as measured from the ends of the radii, 

 have likewise been generally reduced in length ; but, owing to 

 the increased growth of the wing-feathers, the wings, from tip to 

 tip, are commonly longer than in the rock-pigeon. The feet, as 

 well as the tarsi conjointly with the middle toe, have likewise in 

 most cases become reduced ; and this it is probable has been 

 caused by their lessened use ; but the existence of some sort of 

 correlation between the feet and beak is shown more plainly 

 than the effects of disuse. We have also some faint indication 

 of a similar correlation between the main bones of the wing 

 and the beak. 



Summary on the Points of Difference between the several Domestic 

 Races, and between the individual Birds. — The beak, together with 

 the bones of the face, differ remarkably in length, breadth, shape, 

 and curvature. The skull differs in shape, and greatly in the 

 angle formed by the union of the premaxillary, nasal, and 

 maxillo-jugal bones. The curvature of the lower jaw and the 

 reflexion of its upper margin, as well as the gape of the mouth, 

 differ in a highly remarkable manner. The tongue varies much 

 in length, both independently and in correlation with the length 

 of the beak. The development of the naked, wattled skin over 

 the nostrils and round the eyes varies in an extreme degree. 

 The eyelids and the external orifices of the nostrils vary in length, 

 and are to a certain extent correlated with the degree of develop- 

 ment of the wattle. The size and form of the cesophagus and 

 crop, and their capacity for inflation, differ immensely. The 

 length of the neck varies. With the varying shape of the body, 

 the breadth and number of the ribs, the presence of processes, 

 the number of the sacral vertebrae, and the length of the sternum, 

 all vary. The number and size of the coccygeal vertebras 

 vary, apparently in correlation with the increased size of the 

 tail. The size and shape of the perforations in the sternum, 

 and the size and divergence of the arms of the furcula, differ, 

 ihe oil-gland varies in development, and is sometimes quite 

 aborted. The direction and length of certain feathers have 

 been much modified, as in the hood of the Jacobin and the frill 

 of the Turbit. The wing and tail feathers generally vary in 



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