RY PROFESSOR J. T. WILSON. 721 



The solution of the problem of the snout-cartilage at once 

 appears when it is realised by aid of the wax-plate models that 

 the supposed bifurcation of the septum nasi into dorsal and 

 ventral subdivisions is no genuine bifurcation of the structure, 

 the appearance of such being due to a fenestration of 

 the septum. In point of fact, the dorsal and ventral 

 portions do not merely "end in close connection with one 

 another " anteriorly, " where the prenasal plate becomes 

 arrested in the middle line," but they are actually continuous 

 with one another, and it is this, their point of fusion in front of 

 a somewhat spacious fenestra, which constitutes the true anterior 

 border of the septum nasi — ^the extreme anterior limit of the 

 strictly axial portion of the embryonic chondrocranium. 



Further, in his figure 1, Broom represents the two halves of 

 the marginal cartilage of the lip meeting and uniting in front of 

 the oval gap he discovered; and he speaks (p. 558, line 27) of 

 "their anterior union." But previously (p. 557, line 22) he has 

 used the expression " meeting, or almost so, in the middle line." 

 It is the latter alternative which is correct. The marginal strips 

 of opposite sides do not meet in front, though in the adult they 

 maypossibly touch. Thus, in front of what has nowbeen discovered 

 to be the proper anterior edge of the septum nasi there is strictly 

 no cartilaginous tissue present in the mesial plane The anterior 

 edge of the septum is here, as in other mammals, the strict limit 

 of the mesial chondrocranial axis. 



Full demonstration of the correctness of these views is afforded 

 by the study of the wax-plate reconstructions upon which this 

 paper is based. 



A view of the lateral aspect of the septum nasi in Model i., 

 representing the anterior region of the snout of the younger foetal 

 Ornithorhynchus, is given in fig. 1. Tlie internasal fenestra above 

 referred to perforates it so close to its anterior end that only a 

 slender median bar of cartilage forms the extreme anterior portion 

 of the septum. A section across the snout in this plane is repre- 

 sented in fig. 15. The posterior border of the fenestra lies 

 slightly in front of the plane at which the lower edge of the 



