﻿EXTERNAL ANATOMY. RASORIAL FEET. 155 



tion in the foot of the typical Cracidce should hitherto have 

 been completely overlooked, — even by those who have 

 speculated so much on the mode by which the Rasores 

 and the Insessores are united, — is somewhat extra- 

 ordinary ; we can only account for it by the custom of ex- 

 amining specimens set up in cases, or on branches, instead 

 of preserving them in skins, in which state they can be 

 handled in all directions. But however this may be, 

 the fact itself decides the long-contested question as to 

 which family of the Rasores makes the nearest approach, 

 or rather forms the passage to the Insessores; while, if 

 this question be reversed, and it is asked which of the 

 Insessores makes the nearest approach to the Rasores, 

 we need only direct our search among some of the long- 

 legged Brazilian cuckows, or at once point to the sin- 

 gular genus Opisthocomus, 



(133.) The spurs on the feet of Rasorial birds con- 

 stitute one of the most remarkable peculiarities of the 

 order. They are always placed on a line with the pos- 

 terior scales, and appear externally of a bony or horny 

 substance, very sharp and conical in some species, and 

 slightly curved, like a thorn, in others. These appen- 

 dages characterise the male sex, and are used as weapons 

 of defence and offence, chiefly in those battles which 

 take place at the season of courtship. Thus they are 

 analogous, and perform the same functions as the 

 horns of the ruminating quadrupeds, which represent 

 this order in the circle of the mammalia. It is very 

 curious, indeed, to trace the numberless points of ana- 

 logy between these two groups, and to see how nature 

 herself, in despite of their different forms, makes them 

 represent each other. Rasorial birds and ungulated 

 quadrupeds ( Ungulata) are the only vertebrated animals* 

 w r hich defend themselves by kicking at their enemies. 



(134.) The formation of the foot in the order of 

 waders is rather more varied than in the last ; for it is 

 in this group, the most aberrant of the class, that we find 



* The kangaroo also kicks; but then it is a type of the Rasores, in the 

 ordep Glires. See Classification of Quadrupeds, p. 333. 



