Witson and Martin—7he Anatomy of the Muzzle of Ornithorhynchus. 181 
Since Parker’s views represent the sole extant interpretation of these structures 
we shall quote his words for purposes of discussion. 
Referring to the so-called “ duck-bill,” he says :—** Much as it resembles the beak 
of a duck its structure is widely different . . . [the bones| do not, as in the duck, 
finish the margins of the beak, for in that bird, as in its congeners, the bones of the 
upper face run close to the quick that secretes the bony sheath. But the duck-billed 
mammal is quite unique ; the whole outline of the great rostrum is formed by a large 
sheet of solid hyaline cartilage right and left. This extraordinary growth of true 
cartilage in the extended upper lip is quite similar to the growth in the lower lips of 
mammals generally, viz., that slab of cartilage on which the dentary bone grafts itself 
to form the bulk of the solid maxilla inferior.” And he further proceeds —“ We have 
to go down amongst the lower cartilaginous fishes for similar outgrowths of superficial 
cartilage in the region of the mouth.” 
It is not quite clear from the above quotation whether in Parker's view the 
marginal cartilage of the lower lip of Platypus is, or is not, actually the free marginal 
portion of that “slab of cartilage” upon which the dentary has grafted itself. We 
niss, indeed, any special reference to the inferior marginal cartilage of the mandible 
of the adult Platypus on the part of this author. That cartilage, however, though 
analogous in position and function to the cartilaginous basis of the upper lip, we find 
to be essentially different from it, in that it consists only of white fibro-cartilage and 
thus probably possesses no very special morphological importance. 
The strip or sheet of cartilage bordering the upper jaw, on the other hand—the 
“Jarge valance of solid cartilage” as Parker graphically calls it—is composed of true 
hyaline cartilage, and we believe it to have a structural meaning not only different 
from that of the inferior marginal cartilage but wholly different from that suggested 
by Parker. 
If our interpretation of it be correct we have not only zof to “ go down amongst 
the lower cartilaginous fishes” for an explanation of it, but we need not even go 
beyond the pale of the class mammalia to find a key to the solution of this structural 
puzzle. 
The observations which have yielded the results embodied in this paper have 
been carried on both by means of dissections, and by the study of series of coronal 
sections of the snouts of adult animals. We regret that, as yet, we have been unable 
to amplify and corroborate our conclusions by the aid of observations upon young and 
developing specimens, but we believe that, so far as they go, the conclusions arrived 
at will be found sufficiently definite and intelligible to justify their publication. 
The dorsal aspect of the anterior part of the facial skeleton of Ornithorhynchus is 
characterised by the presence of diverging “rostral crura,” as we propose to eall them 
