CHAPTER III 



ADAPTATIONS OF THE BIRD'S SKELETON 



I. Lightness and Tendency to Fusion. § 2. Adaptations to Flight. 

 § 3. Adaptations to Bipedal Progression. § 4. Adaptations of the 

 Skull. § 5. Adaptations in the Backbone. § 6. Muscular System. 



When the term " adaptation " is used to denote a result and 

 not a process, it means a special adjustment of structure or 

 function to meet particular conditions of life. The funda- 

 mental qualities of living creatures are adaptive in the wide 

 sense, for they make for the continuance of the organism 

 in the midst of an inanimate environment, which includes, 

 to say the least, many disintegrative influences. But the 

 term adaptation is convenient to denote less fundamental 

 and more detailed adjustments. The wall of the food-canal 

 is adaptive in so far as it is capable of absorbing the food ; 

 it would not be worthy of the name of food-canal if this 

 were not so ; but the term " adaptation " is conveniently 

 restricted to a particular adjustment such as the presence 

 of thousands of finger-like villi projecting into the cavity, 

 which greatly increase the internal absorbing surface. 



Similarly, bone is a supporting tissue and as such 

 adaptive to the continuance of a large and heavy animal. 

 Especially on land, a bony skeleton, or some other kind of 

 skeleton, becomes indispensable. But it is convenient to 

 keep the term " adaptation " for particular adjustments of the 

 bony skeleton, for instance, in its internal architecture which 

 is adjusted to stand definite strains and stresses, and often 

 shows remarkable economy in the use of material. Still 

 more appropriate is the use of the word " adaptation " when 

 out of a generalised structure, suited for varied uses, a 



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