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 Onii- 

 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 they 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 Oruifhorhynchus." Maeleay Memorial Volume, Linn. Soc. 

 N.S.W. 1893. 



