BY PROFESSOR J. T. WILSON. 719 



of Ornithorhynchus was made by Dr. C. J. Martin in collabora- 

 tion with the present writer (6). 



It was then shown that the " large sheet of hyaline cartilage 

 forming the outline of the great rostrum " previously noted by 

 Kitchen Parker (4), is continuous with the septum nasi. The 

 latter, on being traced forwards in the adult, was found to divide 

 into a smaller dorsal, and a more massive ventral, subdivision. 

 It was shown that the ventral portion descends and is intercalated 

 into the anterior part of the roof of the mouth, and, rapidly 

 widening out, is prolonged forwards into continuity with the 

 large rostral cartilage. This again is continuous laterally with 

 the alinasals, and, extending forwards between the diverging 

 premaxillary crura, spreads both forwards, outwards, and back- 

 wards to form the peculiar marginal cartilaginous support of the 

 upper lip — the "valance of solid hyaline cartilage " described by 

 Parker. The rostral cartilage thus described was identified with 

 the -'prenasal portion of the axis of the embryonic chondro- 

 cranium." The anatomy of the region dealt with was illustrated 

 by a series of figures of transverse sections through the adult 

 snout, and by a drawing iloc. cit., fig. 17) showing the main 

 outlines of the bony and cartilaginous snout-skeleton as seen from 

 the ventral aspect. 



It is now desirable to amplify, and in some measure to correct 

 and reinterpret, the details of the description epitomised above, 

 in the light of further observations, both upon the adult by Broom 

 (7), and upon immature specimens of both Monotremes by the 

 writer. 



Whilst expressing his entire agreement with the interpretation 

 of the rostral cartilage in the adult Ornithorhynchus given by 

 Wilson and Martin, Broom contributed to the anatomical descrip- 

 tion highly important observations "of his own. He found that 

 ^' 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 part 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 



