CHAP THRs 
INTRODUCTION 
Definition.—“ A Bird is a feathered biped.” This popular 
saying undoubtedly furnishes a definition in the world of 
to-day, since no other existing creature has a clothing of feathers, 
and even the word “ biped” is thus superfluous. 
The above should, however, be somewhat expanded, in order 
to shew in greater detail the differences between Birds and other 
Vertebrata. Care must nevertheless be taken to avoid the fault 
common to many modern definitions, of giving an abstract 
of the main characteristics of the object, rather than a clear 
guide to distinction. 
Dr. Gadow ' defines Birds as “ oviparous, warm-blooded, amniotic 
Vertebrates, which have their anterior extremities transformed 
into wings. Metacarpus and fingers carrying feathers or quills. 
With an intertarsal joint. Not more than four toes, of which 
the first is the hallux.” . 
Much of this the beginner might well postpone, his attention 
being solely drawn to the external characters; though of course 
those that are internal are by no means to be subsequently 
neglected. Indeed no satisfactory progress can be made in the 
serious study of Ornithology, or the Science of Birds, without a 
competent knowledge of their Anatomy and Development ; while, 
though at present comparatively few fossil remains of Birds have 
been found, some of them are of the highest importance, and there 
is every probability of future discoveries throwing much light not 
only on the mutual relationships of Birds among themselves, but 
also on their connexion with the Reptilia. Birds are, in fact, only 
extremely modified Reptiles, the two Classes forming the Sawr- 
opsida of Huxley, one of his three primary divisions of Vertebrata. 
1 P.Z.8. 1892, p. 236. 
VOL. IX =z B 
