156 PROF. G. B. HOWES ON jacobson's [Feb. 17, 



under elongation of the snout, with its accompanying specialization) 

 in the manner suggested by Parker himself for the " inter-palatines " 

 of Tarsipes \ 



IV. The foregoing considerations justify us in regarding the 

 palatine process of the mammalian premaxilla, which, be it 

 remembered, enshealhs the organ of Jacobson, and the palatine lobe 

 of the vomer of Caiman niger as, at least provisionally, one and the 

 same element ; and it is necessary now to turn to the latter, by way 

 of inquiring how far its inner capsule may or may not be found to 

 agree with that of the organ named. 



There can be now no doubt that that structure sometimes referred 

 to in the iVmphibia as an organ of Jacobson is a maxillary sinus, 

 non-homologous with the Jacobson's organ of the higher Ver- 

 tebrata. The latter exists, in that which the known facts of de- 

 velopment show to be most nearly its original form, among the 

 Lacertiha. Its general relationships in these animals have been 

 already described (above, p. 153). That the naso-palatine canal of 

 the quadrupedal mammals (c.s., fig. 3) is the representative of the 

 closed duct of the Lizards can hardly be doubted, on comparison of 

 the two types ; it has been shown by Herzfeld. to be regularly 

 absent in some mammals, while the aperture of communication 

 between the body of Jacobson's organ and the floor of the nasal 

 chamber {a.jj , fig. 3), met with in most mammals, is unrepresented in 

 reptiles. On a survey of the known facts, I incline to the belief that 

 the development of the last-named orifice is to be correlated with the 

 loss of communication between the naso-palatiue duct and the body of 

 the organ, and that its appearance may have led up to that suppression 

 of the duct in question seen in some forms (ex. Equus'). Be this 

 supposition worth what it may, the accepted principles of mor- 

 phology forbid our looking upon the Jacobson's organs of Reptiles 

 and Mammals as in any way distinct. 



The vomerine bulla of Caiman niger (vo.'", figs. 2 and 5) occupies 

 an essentially similar position to the body of Jacobson's organ in both 

 Mammals and Reptiles. Its aperture of communication with the 

 nasal pharynx lies, like that of the duct of the Jacobson's organ in 

 the Lizards (and less conspicuously, but no less surely, like that of 

 mammals), within the area of the true posterior nostril. As I have 

 been unable to examine a spirit-preserved head I am not in position 

 to state whether, as seems not unlikely, a tubular duct may have 

 arisen at this point or not. While, however, I have been unable to 

 detect in any other Crocodile the entrance thereabouts of any nerve 

 or blood-vessel such as might conceivably have been transmitted by it, 

 sufficient of the dried remains of its lining membrane was present to 

 enable me to assert, wdth assurance, that it contained a prolongation 

 of the olfactory mucous membrane. This being so, its orifice might 

 be not inaptly compared either to that of the Jacobson's organ of a 



1 Stud. Mus. Univ. Coll. Dundee, vol. i. p. 80 (1890). 

 ^ Herzfeld, loc. cit. p. 556. 



