724 SNOUT OF FCETUS OF MONOTREMES, 



The earlier processes by which the definitive palate of Echidna 

 is constituted have been described in detail by Seydel (9) and 

 illustrated by him from wax-plate reconstructions of this region, 

 in stages considerably earlier to those now under consideration. 

 His fig. 8, taf. XV., may be advantageously compared with figs. 3 

 and 12 of our Models i. and iii., bearing in mind that the latter 

 represent the skeletal structures isolated. On p. 466 Seydel 

 describes the descent of the nasal septum into the plane of the 

 secondary palate : — " Der vorderste Theil der oralen Flache des 

 Septums welcher bei Embryo 46 dem Gaumenloch entspricht, hat 

 sich abwarts in das Niveau der oralen Flache des secundaren 

 Graumens gesenkt, er verschmilzt mit der hinteren Umrandung 

 des Gaumenloches und verschliesst letzteres bis auf die Oeffnungen 

 der beiden Canales naso-palatini." The present models show, 

 however, that in later stages the cartilaginous skeleton of the 

 septum is intercalated in the plane of the secondary palate some 

 little distance in front of the region of the "Gaumenloch," viz., 

 at the triangular depression visible in the figures illustrating the 

 ventral aspect of each of the three models. 



In treating of the formation of the permanent septum nasi, 

 Seydel refers to Newton Parker's observation of an internasal 

 communication in the young of Echidna (3), and he remarks upon 

 this— " Vielleicht erhalt sich diese Communication auch noch bei 

 der erwachsenen Echidna." It is perfectly evident from Parker's 

 own words that he had ascertained this actually to be the case 

 not only in Echidna but in Ornithorhynchus. Seydel is also 

 unaware of the detailed description of this communication in both 

 Monotremes given independently of, and almost simultaneously 

 with Parker, by the present writer (lO). 



II. The prevomer (dumb-bell bone) and the palatine process 



OF THE PREMAXILLA. 



In a paper read before the Society in 1894 (lO) the writer has 

 recorded a number of observations on the anatomy and relations 

 of the so-called "dumb-bell-shaped bone" in Ornithorhynchus. 



