STRUCTURE AND HABITS OF ARCHCEOPTERYX. 283 



animals. I will only add an argument for the benefit of biologists 

 who may be unable to grasp the significance of mechanical considera- 

 tions. The oldest known bird — Archceopteryx — was constructed, so 

 far as the sustentatory apparatus of flight was concerned, on a prin- 

 ciple which has been superseded in all modern birds, and which may 

 therefore be safely pronounced, even ou purely biological grounds, to 

 be inferior in effectiveness to the principle of construction which has 

 superseded it. 



Arclmopteryx was, therefore, not a very good flier. How good it 

 was as a flier, I dare not guess ; though the perfect, but rather small, 

 wings strongly suggest that, in spite of the impediments I have men- 

 tioned (free digits, heavy head and neck, large aeroplanes offering 

 resistance to rapid movement, small muscles, heavy non-pneumatic 

 bones, and deficient respiratory apparatus), Archceopteryx could fly 

 better than the competing pterodactyles. 



Since the days of Archceopteryx, its descendants, or the descendants 

 of its near relatives, have been evolved into the modern bird, which, 

 in its more perfect forms, is a perfect biped and a powerful flier : and 

 a brief enumeration of some of the chief changes involved in that 

 evolution will throw an additional light upon my contention as to the 

 comparatively small power of flight, and as to the quadrupedal loco- 

 motion of Archceopteryx. The shoulder has shifted backwards, the 

 trunk has become shorter, bringing both elbow and knee-joints nearer 

 the centre of gravity; thereby rendering balance in walking or standing 

 independent of the aid of the fore-limb. The foi'e-limb, in accordance 

 with this release from one of its functions, has lost the digits I, II, 

 and III on which that function depended, and has thus been reduced 

 in inertia, while the pelvis has become widened to allow for the back- 

 ward displacement of the abdominal viscera, and the tibia has acquired 

 a cnemial crest of much greater size, enabling the hind-limb to support 

 the weight of the whole body, with the knee flexed and placed in such 

 position that the centre of gravity is behind it. The aeroplanes of the 

 tibiee have been abolished, and that of the tail shortened, lightened, 

 and reduced to a steering apparatus pure and simple. The wings 

 have gained in size ; their inertia has been reduced by the development 

 of air-cavities in the wing-bones ; more powerful muscles have been 

 evolved for the movement of the wings, and this has involved the 



