484 HOMOLOGY OF PALATINE PROCESS, 



figured his anterior paired vomers developing in Erinaceus; and 

 the only difference in the mode of development of the palatine 

 process of the premaxillary in the yoimg marsupial is that in it 

 the bony splint of Jacobson's cartilage is while developing united 

 anteriorly to the premaxillary. 



There is one other bone to which reference need be made in 

 this connection — the so-called " vomer " of the lizard. Most 

 anatomists have regarded this as the homologue of the mammalian 

 vomer. Kitchen Parker, however, though generally referring to 

 the large paired bones in the front of the palatal region in the 

 acertilian skull as "vomers," evidently later recognises their 

 homology with the anterior paired vomers in Erinaceus, and not 

 with the mammalian vomer proper, as will be seen from the 

 passage already quoted. With this homology I entirely agree. 

 It is universally admitted that the organ of Jacobson in the lizard 

 is the true homolgue of that in the mammal, and there can be as 

 little doubt but that the cartilaginous supports, both being 

 developments of the trabecular cornu, are also homologous, so 

 that the homology of the Ijones developed as splints on the median 

 sides of these cartilages in similar situations cannot well be denied. 

 In lizards, moreover, the premaxillary has no palatine process, 

 and the so-called vomer bears a similar relation to the pre- 

 maxillary as does the palatine process in the mammal. In the 

 snake this " vomer " passes up the septum nasi, and even slightly 

 overlaps the capsules of Jacobson; but this is exactly what occurs 

 in Ornithorhynchus, and to a less extent in some rodents. 



It will thus be seen that there is a distinct osseous element 

 developed as a splint on the median side of the cartilage of 

 Jacobson, which in lizards and snakes like the organ of Jacobson 

 itself is well developed and distinct, but which in mammals, 

 probably owing to the great development of the premaxilla in 

 connection with the well formed incisor teeth, usually becomes 

 early anchylosed with that bone, and in many cases even develop- 

 ing in connection with it, forming its palatine process, only 

 remaining distinct in a few forms such as Ornithorhynchus and 

 Miniopteriis. For this ossification which in different forms has 



