360 Prof. Huxley's Lecture 



and the axes of tlie ischia and pubes diverge and lie more or less at 

 right angles to that of the ilium. The ischia alwaj^s unite in the 

 middle ventral line of the body. 



5. In all Birds the axis of the thigh-bone lies nearly parallel with 

 the median plane of the bod}^ (as in ordinary Mammalia) in the 

 natural position of the leg. In Eeptiles it stands out at a more or 

 less open angle with the median plane. 



6. In Birds one half of the tarsus is inseparably united with the 

 tibia, the other half with the metatarsal bone of the foot. This is not 

 the case in Eeptiles. 



7. Birds never have more than four toes, the fifth being always 

 absent. The metatarsal of the hallux, or great toe, is always short 

 and incomplete above. The other metatarsals are anchylosed together, 

 and unite witn one half of the tarsus, so as to form a single bone, 

 which is called the tarsometatarsus. Eeptiles with completely 

 developed hind-limbs have at fewest four toes, the metatarsals of 

 which are all complete and distinct from one another. 



Although all existing Birds differ thus definitely from existing 

 Eeptiles, one comparatively small section comes nearer Eeptiles than 

 the others. These are the Batitce, or struthious birds, comprising 

 the Ostrich, Ehea, Emu, Cassowary, Apteryx, and the but recently 

 extinct (if they be really extinct) birds of New Zealand, Dinornis, 

 etc., which attained gigantic dimensions. All these birds are remark- 

 able for the small size of their wings, the absence of a crest or keel 

 upon the breastbone, and of a complete furcula ; in many cases, for 

 the late union of the bones of the pinion, the foot, and the skull. In 

 this last character in the form of the sternum, of the shoulder-girdle, 

 and in some peculiarities of the skull, these birds are more reptilian 

 than the rest ; but the total amount of approximation to the reptilian 

 type is but small, and the gap between Eeptiles and Birds is but very 

 slightly narrowed by their existence. 



How far can this gap be filled up by a reference to the records of 

 the life of past ages ? 



This question resolves itself into two : — 



1. Are any fossil Birds more reptilian than any of those now 

 living ? 



2. Are any fossil Eeptiles more bird-like than living reptiles? 

 And I shall endeavour to show that both these questions must be 

 answered in the affirmative. 



It is very instructive to note by how mere a chance it is we happen 

 to know that a fossil bird, more reptilian in some respects than any 

 now living, once existed. 



Bones of birds have been obtained from rocks of very various 

 dates in the Tertiary series without revealing any forms but such as 

 would range themselves among existing families. 



A few years ago the great Mesozoic formations had yielded only 

 the few fragmentary ornitholites which have been discovered in the 

 Cambridge Greensand, and which are insufficient for the complete 

 determination of the affinities of the bird to which they belonged. 



