Witson and Martin— Zhe Anatomy of the Muzzle of Ornithorhynchus. 183 
structure of the anterior part of the nose to which he has not referred and which 
render the anatomy of that region less simple than his account would suggest. And, 
further, his work does not refer to the anterior connections of the nasal cartilages, and 
the structural arrangements in the anterior part of the imterval between the rostral 
crura. 
Sir Wm. Turner (17), however, has referred to that interval as filled in by 
“fibrous membrane” “attached behind to the anterior free border of the palate plate 
of each inferior maxilla, at each side to the inner border of the inter-mavxilla, and in 
front it fills up the interval between the recurved tips of the inter-maxille. This 
membrane, therefore, prolongs the palate forwards to the tip of the beak. The edge 
of the dumb-bell-shaped bone is surrounded by the membrane, and is attached by it 
to the anterior free border of the palate plate of the superior maxilla.” 
The only author known to us who seems to have entertained a different view of 
the way in which the inter-crural space is filled up in the recent state, is Briihl 
(18), who in his plates figures the interval as partly filled up by a layer which he 
labels “mem.” with “(car.)” in brackets. 
Of the connection presently to be described between this thin cartilaginous 
lamella and the marginal cartilage of the upper jaw, Briihl gives not the slightest 
indication. In fact he does not seem to have been aware of the very existence of the 
marginal “labial” cartilage. - 
Prior to our acquaintance with this indication in Briihl, simple dissection of the 
space had convinced us of the cartilaginous nature of the layer which Turner has 
described as fibrous membrane, and this conclusion was entirely confirmed by the 
subsequent study of coronal sections (vide figures 1-16). But our investigation 
further revealed the facts, (1) that this lamina of hyaline cartilage is in direct 
continuity behind with the true cartilaginous nasal septum and is therefore a truly 
prenasal element of the axial cranial skeleton, and, (2) that it is in direct continuity in 
front with that “valance of solid cartilage” the superior “labial,” which may, therefore, 
be looked upon as a forward and lateral growth and expansion of the prenasal part 
of the axial skeleton and as no mere labial appendage. 
A study of the figures which accompany this paper will further tend to establish 
the conclusion that originally the inter-crural lamella and the superior “ labial” 
cartilage were continuous, not merely mesially and in front, but also laterally, and that 
interruption of this continuity is due to the growth of the premaxillary as a splint 
grafted on both dorsal and ventral aspects of the continuous cartilaginous plate and 
gradually causing absorption of the latter. Figure 16 taken just at the front of the 
premaxilla where it is deeply grooved anteriorly for the attachment of the labial 
cartilage will sufficiently indicate the sense of this hypothesis. 
