340 MR.W. K. PARKER ON THE STERNAL APPARATUS [June 28, 
But we were informed by Professor Owen at the last Meeting that 
there is no entosternal piece in the sternum of the Bird, but that 
symmetrical bones meet, coalesce, and grow downwards into the still 
cartilaginous keel. I am sorry that this very eminent anatomist did 
not give us the genera in which this occurs ; for, although I have 
been peeping and prying into the secrets of this matter ever since I 
was in my teens, I have only seen this simply symmetrical state of 
the growing sternum in birds of the Ostrich family, e.g. Struthio, 
Dromeus, and Dinornis. In the Fowl-tribe there are five centres, 
three in the Cormorant, in the Plovers (e. g. @dicnemus) three, and 
three in the Passerine and singing-birds, e. g. Turdus, Alauda, and 
their allies, the fastest-growing birds in the class. This matter, how- 
ever, of the number of centres transitionally existing in the sternum 
of the Bird is not the main part of the question. My use of the 
terms is really for the processes in that curious piece of a Bird’s 
framework ; and very convenient terms they are. For the Bird’s 
sternum agrees neither with that of the Batrachian, nor with that of 
the Monotreme, nor with that of the ordinary Mammal, but with 
the same part in the Lizard. In both these groups the sternum is 
one and undivided; but whilst in the Lizard it either continues 
cartilaginous or, as it were, degenerates into granular bone, in the 
Bird it not only ossifies most perfectly, but in a transient manner 
anticipates the segmentation of its homologue in the mammal. 
Now, then, for the phenomena of development in the plastron of 
Chelone midas. There is no connation whatever ; there is no sternum 
at any time, and no hemapophyses—nothing, indeed, but membrane- 
bones formed between the corium and the membrane lining the tho- 
racic abdominal cavity. One bone, the azygous piece, answers to a 
similarly unsymmetrical piece in the thoracic apparatus of the Aves 
and of the Lacertilia, and had its counterpart also in the extinct 
Plesiosaurs and Ichthyosaurs, and also exists in the Monotremes. 
It has long been taken for granted that the merrythought (‘ fur- 
cula’’) of the Bird agrees with the clavicles of the Mammal; in 
most genera, however, it ossifies from only one centre. In some, e. g. 
the Toucan and the Touraco (Ramphastos and Corythaix), and the 
genus Athene amongst the Owls, it is double, as in us and our 
suckling congeners. It is known that the main part of the clavicle 
of the Mammal is only an ossification of fibrous tissue, and does not 
belong to the same category as the scapula and coracoid: so it is 
in Birds, so it is in Lizards, the azygous condition of this part not 
really altering its morphological signification. But the bone, which 
in Lizards and Amphibians has been called the “clavicle,” is an ossi- 
fied cartilaginous rod, and is not the homologue of the Mammalian 
clavicle. Now, whilst suffering both from the Professor’s rebuke 
and from a sense of the pressure of the whole difficulty, it occurred 
to me that it would be best to touch the thing with the point of my 
needle, and see what a little patient labour would reveal. My hap 
was to light upon a guano-mummy of a young Booby, a present 
(along with some flattened and dried Cormorant-chicks) from my 
kind friend Mr. T. J, Moore of Liverpool. 
