1864.] MR. Ww. K. PARKER ON THE STERNUM OF BIRDS. 339 
10. On THE STERNAL APPARATUS OF BIRDS AND OTHER 
VerTEBRATA. By W. K. Parker, F.Z.S. 
At the last Meeting of this Society it was my good fortune to hear 
Professor Owen read a paper on the “ Osteology of the Great Auk 
(Alea impennis).’’ In his description of the sternum, our author 
turned aside to rebuke those anatomists who applied the terms used 
in the description of the Tortoise’s breastplate to the parts of the 
Bird’s sternum. I was very glad to be reminded of the confusion 
which exists in the nomenclature of the shoulder- and breast-bones 
in the Vertebrata generally ; and as I have always used Geoffroy’s 
terms, episternal, hyosternal, &c., in my published descriptions of 
the sternum of birds, I thought it would be well to re-examine the 
matter. 
In my paper on the Baleniceps I quoted Professor Owen’s views 
as to the nature of the Chelonian breastplate; and therefore, whilst 
still using the old familiar terms, I did so with open eyes, choosing 
them for the bird, although I knew that they were inapplicable to 
the bones that appear in the same region in the Tortoise. The 
question is, Is it fair to use the cast-away terms of one class for the 
analogous, but not homologous, parts in another? I will quote Pro- 
fessor Owen’s own writings to show how these threads of scientific 
thought came to be ravelled. In the ‘ Descriptive Catalogue of the 
Skeletons in the Museum of the College of Surgeons’ (vol.i. p. 169, 
no. 769), Prof. Owen, in describing the skeleton of Chelone midas, 
says, “ The plastron consists, in the genus Chelone, as in the rest of 
the Order, of nine pieces—one median and symmetrical, and the 
rest in pairs. With regard to the homology of these bones, three 
explanations may be given—one in conformity with the structure of 
the thoracic-abdominal cage in the Crocodile, the other based upon 
the analogy of that part in the Bird, and the third agreeably with 
the phenomena of development. According to the first, the median 
piece of the plastron, called ‘ ento-sternal,’ answers to the sternum 
of the Crocodile, or ‘ sternum proper,’ and the four pairs of plastron- 
pieces to the hemapophyses forming the so-called sternal and ab- 
dominal ribs of the Crocodile. Most comparative anatomists have, 
however, adopted the views of Geoffroy St.-Hilaire, who was guided 
in his determination of the pieces of the plastron by the analogy of 
the skeleton of the Bird, according to which all the parts of the pla- 
stron are referred to a complex and greatly developed sternum, and 
the marginal plates are viewed as sternal ribs (heemapophyses). The 
third ground of determination refers the parts of the plastron, like 
those of the carapace, to a combination of parts of the endo-skeleton 
with those of the exo-skeleton.” 
It is evident from this quotation that Geoffroy, in the first instance, 
took his cue from the sternum of the bird—most likely from the 
structure of the sternum in the chick; if so, where is the absurdity 
of retaining his familiar and useful terms for the parts and processes 
of the ornithic sternum, and of allowing the Tortoise to crawl off 
in some other direction to get names for his nine-jointed breastplate? 
