BY R. BROOM. 
557 
In a recent paper* Wilson and Martin have carefully described 
some of the chief points in the anatomy of the muzzle of Orni- 
thorhynchus. They have dealt principally with the structure and 
relations of the large rostral cartilage. By a series of transverse 
vertical sections the authors show that the nasal septum on pass- 
ing forward divides into a slender upper and a well developed 
lower part, and that this latter being continued forward, broadens 
out and becomes the rostral cartilage. For a short distance the 
rostral cartilage is shown to be clasped between the premaxillaries, 
recalling the condition of the embryonic bird. From this relation- 
ship and from the fact of its being a continuation of the nasal 
septum, the rostral cartilage is held to be an enormously developed 
prenasal. With their view I must express my entire agreement. 
While my researches confirm the accuracy of the sections figured 
by Wilson and Martin, they reveal an interesting point apparently 
not observed by these authors. The rostral cartilage does not 
extend forward to the front of the beak as an entire sheet. 
Almost immediately in front of the plane passing through the 
anterior parts of the premaxillaries the cartilage becomes abruptly 
arrested in the middle line; but while this is so, the lateral parts 
extend forward almost to the front of the beak, where they again 
approach each other, meeting, or almost so, in the middle line. 
There is thus left in the middle an oval space entirely free from 
cartilage. This arrangement I have found in three different 
individuals (two males and one female). The lateral portions of 
the cartilage curve round backwards along the outer sides of the 
rostral crura, supporting the lip as shown by Wilson and Martin. 
It seems probable that this whole complicated marginal cartilage 
is a development of the prenasal, for though in the Skate the pre- 
nasal rostrum supports a pair of labials at its anterior part, in the 
higher forms when labial cartilages are present the} 7 never seem to 
have the same relations to the premaxillaries as is found in the 
Platypus. 
* J. T. Wilson and C. J. Martin. " Observations upon the Anatomy of 
the Muzzle of Ornithorhynchus," Macleay Memorial Volume, Linn. Soc. 
N.S.W. 1893. 
