MOEPHOLOGT OF OPISTHOCOMUS CEISTATUS. 47 



the tail, birds are like Plesiosaurs ; but in the structure of their skull, and I believe 

 also, that I may state in the development in their fore limbs of intercalary digits, they 

 resemble the Ichthyosaurs. 



Like the Chelonia, Tertiary and existing birds have lost all traces of teeth and have 

 horny jaws ; and like the Crocodile's embryo, and the adult Hcttteria (Sphenodon), the 

 hyoid arch and the columella auris become continuous. The superficial parts of the 

 shoulder-girdle of a bird, its parostoses, are like those of an Ichthyosaurus, an 

 ordinary Lacertian, and of the Monotrematous Mammalia; but, as a rule, these are 

 fused together. Moreover, these parts do not remain in their primitive distinctness; as 

 a rule they graft themselves upon proximal remnants of the antero-inferior fork of the 

 shoulder-plate (precoracoid). I have lately shown (Proc. Roy. Soc. 1888, pp. 397- 

 402) that the skull of a bird is rich with the remains of truly Amphibian structures ; 

 indeed, it is far more Amphibian in its very foundations than any existing Reptile ; the 

 parasphenoid of a Frog and of a Bird closely correspond. Then there are the 

 remnants of the ethmo-palatines and certain superficial structures that, as a rule, 

 have been got rid of even in Reptiles. The one or even two rows of supra-orbital 

 bones are remarkable ; but still more so is the fact that the long jugo-maxillary chain 

 of ganoid bones seen in Lepidosteus is represented in some birds (Emu, Owl, Heron, 

 Cormorant) by a chain of four bones behind the premaxillary, namely, the maxillary, 

 postmaxillary, jugal, and quadrato-jugal. In the palate, also, besides the endoskeletal 

 postpalatines of the Passerine birds and the medio-palatine of the Woodpeckers (pre- 

 formed in cartilage), we have in the latter birds especially, and also in others, a literal 

 crop of vomers, such as we see also in the Marsupials among the Mammalia. Even 

 these parosteal remnants are too valuable to be lost sight of or left as unrelated ; they 

 at once remind the Morphologist of what is seen in the generalized pavement of bones 

 under the rostrum of a Sturgeon. 



It is quite certain that not the least patch of bone-cells is ever diflferentiated and 

 isolated accidentally ; as a matter of observation in birds, the smallest of such patches 

 is very uniform in its appearance in various genera and families. One more fact in 

 evidence of what I am anxious to express — namely, that birds did not appear during 

 time, as a sort of feathered sport in a truly reptilian type, but from some low, genera- 

 lized Amphibian or Dipnoan, is to be seen in a character now to be described. The 

 earliest embryo I have examined of this type has a dilated suprascapula, separated 

 from the scapula by an arched line of smaller cells, and overlapping the scapula 

 proper at its edges. This upper element is, for a short time, quite as distinct as in 

 the Frogs and Toads ; lower down, in the Rays, among the Elasmobranchs, the supra- 

 scapula is perfectly segmented off from the scapula (see ' Shoulder-girdle and Sternum,' 

 1868, pis. i. and v.). I have one more preliminary remark to make which bears 

 directly upon the relation of Birds and Reptiles, and that is in the clear evidence we 

 have of secular shortening of certain parts. In some birds, for instance the Humming- 



