SUCCESSION OF MAMMALIAN TEETH. 439 



represent the apparent or physiological, and not necessarily 

 the true, relationships between their component teeth. 



A very interesting paper published in 1868 by Lankester 

 and Moseley (47) criticised these views of Owen's and 

 suggested, with a good show of reason, a new system 

 of nomenclature, which although of great interest has never 

 been adopted. 



Owen's subdivision of the mammalian dentition into two 

 types, the monophyodont and diphyodont, implying respectively 

 the presence of one set only or two sets of teeth, has endured 

 until quite recently, although it was shown as long ago as 

 1869 by Flower (6) that this generalisation was incorrect. 



His views as to the relation of the milk and replacing 

 teeth vary considerably in his earlier and later works ; thus 

 we find him at one time stating that the marsupials possess 

 milk incisors which are shed early in life, while in his latest 

 works he says (4, p. 379) that the functional incisors, canines 

 and deciduous molars of these animals are possibly to be 

 referred to the first or milk dentition ; l this, taken in con- 

 junction with another statement which he makes (4, p. 

 368), viz., that "the molars are a continuation backwards 

 of the primary or milk series," shows that Owen in 1868 

 anticipated those views put forward as original in the 

 last few years by various continental observers, which have 

 received such universal acknowledgment. 



Next to Owen in this country we are indebted to 

 Flower for a great advance in our knowledge of this subject ; 

 the latter was the first to study the fcetal dentition in the 

 flesh, and he by this means definitely determined the exact 

 number of replacing teeth in the marsupials (7). From the 

 study of the relations of the- two dentitions in those animals 



1 The detailed description which Owen gave of the shedding of the 

 supposed milk incisors (3, 5) leads one to think he must have had some 

 evidence to go upon in making this statement. Recently I have described 

 the presence of some additional vestigial incisors in M. major (12), and it 

 seems just possible that Owen may have come across specimens in which 

 these were abnormally developed and mistaken them not unnaturally for 

 the deciduous incisors. His sudden change of opinion may have been due 

 to the appearance of Flower's investigations (7) although he does not refer 

 to them. 



