DIRBCTIONS FOR MEASUREMENT. 57 



birds, there is a slight elevated point right in the middle; this, or the posi- 

 tion of it in other birds, is the precise place. Place the otlier foot of the 

 dividers over the transverse line of jointing of the base of the middle toe. 

 This latter point, in all birds, when the toes are bent backward, becomes a 

 more or less salient angle easily determined. In hard-legged birds it is 

 usually indicated by the termination, of last tarsal sciitellum ; in water birds, 

 there will be seen a little crosswise nick, showing just where the skin has 

 shrunk into the crack between the end of the metatarsus and the Ijase of 

 the toe. It will be evident that a measurement taken as here directed will 

 not always be the same as one taken" behind, up over the convexitj' of the 

 heel, and down to the level of the sole ; but there are behind no otlier 

 tangible points of termination. (See fig. 9, (rs.) What, now, is the mean- 

 ing of the expression — "l>. = i irs." ? 



§ 103. "Length of toes." Distance in a straight line along the upper 

 surface of a toe, from the point last indicated, to the root of the claw on 

 top> Observe that, as the claws are inserted upon the ends of the toes, 

 somewhat as the uails are on our fingers, this measurement is a different 

 thing from one taken along the under surface of the toes. Alwa^'s make 

 it with the dividei-s. Length of toe is always taken ivitJiout the claw unless 

 otherwise specified. When no particular toe is specified, ot is always 

 meant. (See fig. 9, dtcl.) Define this expression: — " trs.> ?ji.'" 



§ 104. "Length of the claws." Distance in a straigld line from the 

 point last indicated to the tip of the claw. (See § 101.) When this 

 measurement is meant to be included in the length of toe, I say Id. 

 Determine this : — "trs. < ild." 



§ 105. "Length of head" is an often convenient dimension for compar- 

 ison with the bill. Set one foot of the dividers on the base of culmen 

 (determined as above), and allow the other to just slip snugly down over 

 the arch of the occiput. This is the required measurement. What does 

 this mean: — "M. = 6."? 



§ 106. All measurements are in the English inch and vulgar fractions 

 or decimals, unless otherwise specified. 



§ 107. Finally, it may be well to call attention to the fact, that most 

 persons unaccustomed to handling birds are liable to be deceived in attempt- 

 ing to estimate a given dimension ; they generally make it out less than 

 measurement shows it to be. This seems to be an optical effect connected 

 with the solidarity of the object, as is well illustrated in drawin"- plates of 

 birds, which, when made exactly of life-size, always look larger than the 

 original, on account of the flatness of the paper. The ruler or tape-line, 

 therefore, should always be used, and are more particularly necessary in 

 those cases where analyses in the Key rest upon dimensions. It is hardly 

 necessary to add, that in taking, approximately, the total leno-th from a 

 prepared specimen, regard should be had for the "make-up" of the skin. A 

 little practice will enable one to determine pretty accurately how much a 

 skin is stretched or shrunken, and to make the due allowance in either case. 



KEY TO N. A. BIRDS. 8 



