550 MAMMALIAN AND REPTILIAN VOMERINE BONES, 



and only slightly less developed than the foetus studied by Parker. 

 The premaxillaries were well developed, and had large palatine 

 processes which ran far back by the sides of Jacobson's cartilages, 

 but there was no trace of a distinct " anterior vomer," and in the 

 gradual thinning of the plates as they pass backwards there was 

 prett}'- conclusive proof that the plates had been ossitied from the 

 premaxillaries. 



It seems probable to me that -further research will show that 

 in none of the Insectivora are there any distinct "anterior 

 vomers," but on the other hand it is quite likely that Parker is 

 right in finding distinct "anterior vomers" in most of the 

 Edentates. 



In only a very few of the higher mammals have we any record 

 of the palatine process being formed from a distinct centre. 

 Howes records it in the case of the rabbit, and Schwink in the 

 fcetal sheep. Probably some other instances will be recorded. 



In the Chiroptera we find a distinct palatine process very 

 generally absent, owing, no doubt, to the fact that Jacobson's organ 

 is as a rule wanting, and also to the fact that the premaxillaries 

 frequently do not meet in the middle line. In Miniopteras, one 

 of the few bats in which the organ of Jacobson is known to occur, 

 we have the cartilage of the organ supported by a median bone 

 almost exactly after the manner of the dumbbell bone in Orni- 

 thorhynchus. As in Ornithorhynchus, too, this median bone is 

 formed by the anchylosis of a pair of bony splints. And, though 

 in adult life such extensive anchylosis takes place that even the 

 vomer becomes anchjdosed to the maxillaries, the little median 

 bone remains quite free. 



It will thus be seen that while in most mammals the cartilage 

 of Jacobson's organ is supported by a bony process from the 

 premaxillary, in a few forms {Orniihorhynchus^ Minioj^terus), the 

 cartilage is supported by a distinct element ; while in others 

 apparently we have an intermediate condition in that the element 

 which supports the cartilage is at first independent, and then 

 anchyloses with the premaxillary to form its palatine process. 



