720 SNOUT OF FCETUS OF MONOTREMES, 



the beak, where they again approach each other, meeting, or 

 ahuost 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 back- 

 wards 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. . ." 



Broom's interpretation of his facts is worthy of special remark, 

 since its correctness is largely borne out by the facts of develop- 

 ment as shown by the reconstructions of the foetal snout now 

 figured. Referring to the dorsal subdivision of the nasal septum, 

 he says : — " Though in the region of the anterior nares it is 

 considerably removed from the prenasal plate " [which is con- 

 tinuous with the ventral moiety of the septum nasi] "on passing 

 forwards it approaches the latter, and ends in close connection 

 with it, at the point where the prenasal becomes arrested in the 

 middle line. This point" [marked with an asterisk in his fig. 1, 

 which should be consulted] "probably represents the anterior 

 end of the beak in the ancestor of the Platypus, as not only do 

 the two cartilages here end together, but this is practically where 

 the two premaxillaries would meet if they came together. Con- 

 nected with it, moreover, there is a further feature of importance. 

 On the upper side of the beak in the middle line is a small 

 thickened area of epithelium (c in fig. 1 ) unlike that of the rest 

 of the beak. This is probably the remains of the caruncle. If 

 it be so, and it is quite perceptible to the naked eye, it corrects 

 the statement of Owen's that no trace of the caruncle can be 

 found in the adult. Whatever be its signification, it is evidently 

 closely related to the supposed apical point of the primitive beak, 

 as a series of fibrous bands pass from it to the latter." 



It will presently be shown that the actual condition as seen in 

 the developing snout very nearly corresponds to this interpreta- 

 tion. 



