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ON THE SKELETON OF THE SNOUT OF THE 

 MAMMARY FCETUS OF MONOTREMES. 



By Professor J. T. Wilson, M.B., Ch.M. ' 



(Plates xxxvii.-xlii.) 



At the Meeting of the Society, held March 28th, 1900, I 

 exhibited photographs and wax-plate reconstructions illustrating 

 the anatomy of the snout of the so-called mammary foetus of 

 Ornithorhynchus and Echidna. A brief preliminary account of 

 the conclusions arrived at was published in the Proceedings of 

 the Society (i). 



The present paper aims at presenting a more ample and detailed 

 account of the facts, accompanied by the necessary illustrations. 



The material employed in the investigations which form the 

 subject of this paper included, in addition to adult specimens of 

 both Monotremes — (A) the snout of a "mammary foetus" of 

 Ornithorhynchus, whose external characters were described by me 

 in a former communication to the Society (2), and which was 

 originally placed at my disposal by the Trustees of the Australian 

 Museum; (B) a "mammary foetus" of Echidna of almost precisely 

 the same stage of development as the younger of two specimens 

 described and figured by Professor W. Newton Parker (3). Both 

 Professor Parker's and my specimen were obtained by the 

 courtesy of the Trusteesof the Australian Museum, though atwidely 

 different times. (C) Another and" larger " mammary foetus " of 

 Echidna in my possession I owe to the generosity of my colleague 

 Professor W. A. Has well, F.R.S. (D) Through the kindness of 

 Mr. J. P. Hill I have had access to a series of coronal sections of 

 the snout of a larger " mammary foetus " of Ornithorhynchus, of 

 almost the same size and general stage of development as that 



