150 ON THE "dumb-bell-shaped" BONE IN ORNITHORHYNCHUS. 



Lettering of Jigs. 6-12. 



mx., maxillary palate; m. mx., median anterior process of maxillary 

 palate ; v. , vomer ; d. h. v. , vomerine spur of dumb-bell bone ; d. b. p. , 

 posterior seginent of dumb-bell bone ; d. h. a., anterior segment of dumb- 

 bell bone ; d. b. ^., isthmus of dumb-bell bone ; /. o., organ of Jacobson ; 

 gl., glandular ridge; 7m., nerves; n.p.f., naso-palatine foramen; n.c, 

 nasal cavity ; a. s., ali-septal cartilage ; «./., cartilage of nasal floor ; n.s., 

 nasal septum ; i. a., internasal aperture. 



The figures were drawn by Mr. G. H. Barrow, those of the dumb-bell- 

 shaped bone from nature, those of the coronal sections from photo-micro- 

 graphs. 



Appendix (Jtdy 23rd, 1894-) ■' — J"st on the eve of the final 

 revision of the proofs of the foregoing pages there came to hand 

 by the English mail, P.Z.S. 1894, Part 1 (June 1st), containing 

 Prof. W. Newton Parker's paper, " On some Points in the Struc- 

 ture of the Young of Echidna acideata" to which the Editor has 

 kindly called my attention. In this paper the author refers to 

 the internasal aperture described above and states that "a com- 

 munication between the two nasal cavities has been described by 

 Home in Ornitho7'hynchus. Zuckerkandl was unable to observe 

 this ; but I have satisfied myself that both Monotremes agree in 

 this respect, and that the left and right nasal chambers com- 

 municate by a slit-like passage beneath the septum just behind 

 Jacobson's organ." In view of these observations I can only 

 regret that it is impossible now to withdraw the words " hitherto 

 undescribed" from the title of ray paper. It is curious that 

 Home's observation should have been passed over in silence by 

 well nigh every later writer on Ornithorhynchus. 



The present paper was communicated to the Linnean Society of 

 N.S.W. at its meeting on 25th April, 1894, a preliminary note 

 having been read at the previous meeting on 28th March. Pro- 

 fessor Parker's paper, although published only on 1st June, 1894, 

 was i-eceived by the Zoological Society of London on 7th Nov., 

 1893, and read at the Society's meeting on 16th Jan., 1894. 



