CHAPTER XII. 



DIMENSIONS, 



IN this list the birds are for the first time arranged in the order of 

 their average size, with their chief dimensions reduced to 

 decimals of their length. Though birds vary much in stature, they 

 vary very little in their proportions, and thus their measurement put 

 in this way is an important aid in their identification. 



The double letters have been adopted to avoid any confusion that 

 might arise from having two series of numbers running through the 

 book. The length is taken from the tip of the beak to the tip of the 

 tail. The wing measurement is that of the one wing, not of the wing- 

 spread, which is a most difficult thing to measure accurately. The tail 

 is measured from the pygostyle, which is perhaps more generally 

 known as the " ploughshare bone." The body is measured from the 

 base of the beak to the pygostyle. The beak is measured along its 

 culmen, or upper edge ; and the tarsus, which, as we have said, 

 is really the tarso-metatarsus, is measured from the ankle joint, 

 popularly and erroneously called the " knee," to the junction with the 

 toes, which is, quite as erroneously and popularly, known as the 

 " heel." 



It is hardly necessary to point out that the measurement in inches 

 should be divided by the length in inches to obtain these figures, 

 and that consequently these decimals have merely to be multiplied by 

 the length to obtain the actual dimensions. If, for instance, a Lesser 

 Whitethroat should be found only 5 inches long, the figures in the list 

 should be multiplied by five, and its wing should be 2'6 in. ; its tail 

 2'3 in. ; its body 2-4 in. ; its beak -3 in. ; and its tarsus "8 in. ; which 

 are in the same proportion as if the bird had been of the average size 

 of 5j inches. 



Proportions. 



