Chap. V. SUMMARY OF DIFFERENCES. 187 



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 

 Haces, 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 pre- 

 maxillary, nasal, and maxillo-jugal bones. The curvature of 

 the lower jaw and the reflection 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 in- 

 dependently 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 oesophagus 

 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 vertebra, 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 perfora- 

 tions in the sternum, and the size and divergence of the arms 

 of the furculum, differ. The 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 length together, but sometimes 

 independently of each other and of the size of the body. The 

 number and position of the tail-feather vary to an unparalleled 

 degree. The primary and secondary wing- feathers occasion- 

 ally vary in number, apparently in correlation with the 

 length of the wing. The length of the leg and the size of 

 the feet, and, in connection with the latter, the number of 

 the scutellae, all vary. A web of skin sometimes connects 

 the bases of the two inner toes, and almost invariably the two 

 outer toes when the feet are feathered. 



The size of the body differs greatly : a Bunt has been known 



