482 
HOMOLOGY OF PALATINE PROCESS, 
In man a somewhat similar condition exists, though he differs 
from Pteropus in having a rudimentary organ of Jacobson. Here 
there is no palatine process to the premaxillary, and the rudi- 
mentary recurrent cartilage — the plough-share cartilage of Huscke 
— is not supported by a distinct bone; but in a human foetus of 
10 weeks I have found on the inner side a small tract of osteo- 
genetic cells very similar in position to those in Trichosurus, but 
here ossified by an invasion from the vomer. 
In Ornitliorhyvchvs we find still further evidence of the 
vomerine nature of the bony support of Jacobson's cartilage. 
Here in the adult we find the capsule of Jacobson's organ 
supported by the median " dumbbell-shaped bone " — a structure 
which bears a very marked resemblance to the little median bone 
lying between the organs in the bat. Since its first discovery 
this peculiar dumbbell-shaped bone has been the subject of very 
considerable discussion as to its true nature. Three different 
opinions have been expressed with regard to it, but as one of 
them — that homologising it with the prenasal bone of the pig — 
has been abandoned by its author, and is known to be founded 
on a misconception, only the other two need be discussed. The 
view which has received almost universal support — that of 
Rudolphi, Meckel and Owen— is that it is the inner part of the 
premaxillary and the homolo<jue of the palatine process of the 
premaxillary in the higher mammals. In more recent times 
Albrecht,* Turner,! Flower \ and Symington§ have advocated the 
same view, and have adduced arguments which practically amount 
to conclusive proof of the correctness of their position. The other 
view which has been expressed as to its nature is that recently 
* Loc. cit. 
f W. Turner, " The Dumbbell-shaped Bone in the palate of the Ornitho- 
rhynchus compared with the Prenasal Bone in the Pig." Journ. Anat. and 
Phys. Vol. xix. 
J W. H. Flower, "Osteology of the Mammalia." 3rd Ed. Loud. 1885. 
§ J. Symington, £< The Nose, the Organ of Jacobson, and the dumbbell- 
shaped bone in Ornithorhynchus." Proc. Zool. Soc. 1891. 
