Bawden, Nose and Jacobsoris Organ. itf 



not directly as here, into the oral cavity, but into the general 

 cavity of the nose proper. These relations are well shown in 

 the model of Hyla versicolor ; Fig. 4, Plate XI, and Fig. 5, 

 Plate VIII. 



In the lizards Jacobson's organ is described as a small 

 paired cavity lined by olfactory epithelium from the floor of 

 which a papilla arises. This papilla is shown in Fig. 6, Plate 

 IX, in Entcenia, and in Fig. 3, Plate IX, pap. It communicates 

 with the mouth by a special aperture in front of the internal 

 nares. See Euttzm'a,Figs. 3 and 4, Plate IX, ap. Beard (No. 1) says 

 "It is now a fact that Jacobson's organ of reptiles is a specially 

 differentiated part of the nose" but that "it must be an incom- 

 parably finer sense-organ than their nose proper." It is best 

 developed and most functional in Lizards, Figs. 2-6. Plate IX 

 shows these general relations in Reptilia, in Eutaenia and black 

 snake embryos. It is noticeable that in Lacertilia the parietal 

 eye and Jacobson's organ are both functional, whereas in Anura 

 and Urodela (Amphibia in general) both are degenerated or un- 

 developed, The question arises whether the diverticle is a de- 

 generated Jacobson's organ, or Jacobson's organ a developed 

 and perfected diverticle. We incline to believe the latter to be 

 the true statement of the case. There is a remarkable gap in 

 this respect between the two groups of Reptilia, Ophidia and 

 Lacertilia on the one hand and Chelonia and Crocodilia on the 

 other hand ; the former possesing a Jacobson's organ so highly 

 differentiated and the latter possessing only a rudimentary organ 

 which until recently has defied detection in Crocodilia. This 

 discovery was made by C. Rose, " Ueber das rudimentare Jacob- 

 son'sche Organ der Crocodile und des Menschen." Anat. Anz. 

 VIII, 14, 15, June, 1893. (No. 22.) 



Further the two groups in which Jacobson's organ is well 

 developed are, aside from its development, endowed with a very 

 simple nose proper as compared with the conditions as found in 

 Crocodilia and Chelonia. It appears that these two things were 

 related in some way. Perhaps the nose proper of these two 

 groups has a simple structure because of the high development 

 and extreme delicacy of their Jacobson's organ, and Crocodilia 



