EXTERNAI. ANATOMY. RASOBIAL FEET. 155 
tion i n the foot of the typical Cracida should hitherto have 
been completely overlooked, — even by those who have 
speculated so much on the mode by which the Rasorex 
and the Jnsessores sfre 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 aU directions. But however this may be, 
the fact itself decides the long-contested question as to 
which family of the Rusorex makes the nearest approach, 
or rather forms the passage to the Inxexxores; while, if 
this question be reversed, and it is asked which ot the 
Insessorex makes the nearest approach to the Rnsorex, 
we need only direct our search among some of the long- 
legged Brazilian cuckows, or at once point to the sin- 
gular genus Opisthocoinus, 
(133.) The xpurs 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 ot 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 otfence, chiefly in those battles which 
take place at the season of courtship. '1 hus 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 ( Unyulata) are the only vertebrated animals 
which 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 R 
in this group, the most aberrant of the class, that we nc 
* The kangaroo also kicks : hut then it is a type of tlie RasoreS) in the 
order Glires. See Ciassiticalion of ^jnadrupeds, p. 333. 
