82 PEOF. W. K. PAEKEE, ON THE 



hyoid arch is not only essentially the same as that of Hatteria, but the descending bar 

 of cartilage, which is aborted in the middle in all birds, is in it unusually large and 

 shows signs of secular shortening by its folded or puckered condition. The vertebral 

 chain has the same development as in Gallinaceous birds generally; its dorsals are 

 cylindroidal, but so also are those of the Tinamou, the Ratitse, and, as I have just 

 mentioned, Hesperornis, a bird so long extinct ; hence it is evident that this peculiarly 

 avian structure is extremely ancient. The appendages of the ribs are not typical; 

 they, however, are well seen in Hatteria and, to some degree, in the Crocodiles, whilst 

 they are absent in Gliauna — an archaic Chenomorph. 



Those parts of the body which, becoming transformed for the purposes of flight, 

 dominate all the rest of the organism— the sternum, shoulder-girdle, and wings — are, 

 in this bird, so very instructive as to make it very precious to the Morphologist : in 

 this it has no peer. 



The sternum, in the backward position of its small keel and the feeble development 

 of the postcostal or metasternal region, is an intermediate structure between that of a 

 Bird and that of a Lizard. So also is the shoulder-girdle in all its parts and relations ; 

 besides which the scapula is developed in the same manner as in the Frogs and Toads. 

 The wings in the embryonic stage not only have the claws of the first and second digits 

 nearly as large as in the foot, but there is, as in the Ostrich and Rhea, a rudimentary 

 unguis on the third half-aborted digit, and a phalangeal remnant of a fourth digit ; a 

 metacarpal remnant is seen in the Fowl and several other birds. The carpus, as in a 

 few other birds, is, for a time, divided into at least seven segments, and is then essen- 

 tially like that of an Amphibian or a Chelonian. 



For a time the pubis strives to attain to an Ornithoscelidan length ; after the middle 

 of incubation it acquires its proper relative avian length, But the history was taken 

 up at its middle — at the middle, actually, of incubation ; it is, however, in the still 

 earlier stages that the ontogeny of this Class is seen most clearly ; those earlier stages 

 have had to be worked out in less archaic types. The true Archmopteryx is lost in the 

 almost infinite past ; the " so-called Arclimo])teryx " is very doubtful as a parental 

 form. It does, however, help us to imagine how the vertebral internodes became 

 aborted and partly suppressed, so that a feather-shaped tail became fan-shaped, the 

 rectrices being set in a semicircle instead of growing out of the sides of a long 

 Reptilian tail. We have, however, nothing intermediate between these two types of 

 tail even in the Cretaceous birds. Something of the same sort has occurred in the 

 limbs. If the limbs of Ceratodus may be taken as a pattern of an ichthyopterygium 

 there has been a secular shortening of some, and suppression of other, axial parts or 

 internodes : thus we get the shortened radiating fan-shaped limb — the proper cheiro- 

 pterygium ; that, in turn, had to be tiansformed into the avian fore limb or wing. 



