BIRDS. 145 



be seen, either azygous or symmetrical, in several Mammals. The other centres, however, the 

 " lophosteon," the " urosteon," and the " coracostea/' are, I believe, absolutely ornithic, having 

 no counterparts in other Vertebrata than Birds. 



The sternal ribs are ossified by ectosteal deposits at first, like the vertebral ribs, the only 

 exception being in the Penguins (see Plate XIV, fig. 1) ; in these Birds the sternal ribs are affected 

 by endostosis first and afterwards by ectostosis. In all Birds, the Penguin not excepted, they 

 become thoroughly ossified very early, and are articulated both to their vertebral counterparts 

 and to the Sternum by synovial joints. There are no "costae intermedia" in Birds, and the 

 vertebral ribs develop retral autogenous appendages in all but the Palamedeee. It has been 

 shown that in the Anoura the Sternum in some cases has an ectosteal sheath, as in the Frog ; 

 and in others only an internal deposit, as in the Toad (see Plates V VII). We saw no instance 

 of any outer plate of bone, however, in the genuine Reptiles. 



There is great variation in this respect in the Mammalian Sternum, for whilst the Mono- 

 tremes, Marsupials, Rodents, Insectivores, Carnivores, and Cetaceans, have their sternal pieces 

 ossified as shaft-bones originally, in the other Orders the deposit, even when the ossification 

 is at length very perfect, always appears like an epiphysis at first. 



As to Birds, in the Ostrich tribe and in the Gallinacese the first deposit is by ectostosis 

 (see Plates XVI, XVII), hence the definiteness of their bony centres ; in all the other tribes, as far 

 as I have seen, even in the Pigeons, so near akin to the Fowls, the deposit is internal at first, 

 and it is deposited in two layers, with cartilage within and on the outside, as in all the Reptilia 

 proper. 



Contrary to what occurs in these latter Cold-blooded creatures, these endosteal tracts 

 grow with extreme rapidity in the Bird, and thus a certain nick of time has to be found in 

 which their distinctness may be seen ; moreover, soon after the fast-growing fledgling of an Aerial 

 Bird has taken to its wings the ectosteal layer commences, ultimately giving the bone as complete 

 & finish as is seen in the Sternum of the Ostrich and the Fowl. 



I 



Family SPHENISCIN^E. 1 



Example. Eudyptes ? 



The Shoulder-girdle and Sternum of a young Penguin (probably E. chrysocome) is figured 

 in Plate XIV (fig. 1, three quarters natural size; fig. 2, twice natural size; and fig. 3, natural 

 size). The scapula (sc.) is very broad, quite unlike what is typical amongst Birds, its supra- 

 scapular region (s. sc.) is still soft, as is the glenoid region and the small meso-scapula (m. sc.). 

 The coracoid (cr.) is a very stout rod of bone ; its head and its epicoracoid region (e. cr.) are 

 still soft ; from its head there proceeds a large falcate segment, the " proximal prse-coracoid " 

 (p. p. c.), which is attached to the antero-external margin of the clavicle, but is at present quite 



I here use no particular classification, but place my instances in such groups as seem to be 

 most natural ; as to the terms " Order," " Family," &c., I lay no great stress upon them, merely using 

 them for convenience' sake. I must refer the reader to Professor Huxley's forthcoming Paper, in the 

 ' Zool. Proc.,' for Lis views on the arrangement of the members of the Bird-Class ; it was read in on 

 April llth, 1867. , 



19 



