502 H. W. NORRIS AND SALLY P. HUGHES 



five olfactory epithelium. In brief, in the Amphibia in general, 

 the posterior ventral olfactory glomeruli are related to Jacob- 

 son's organ, but not exclusively so. In Herpele and Geotrypetes, 

 however, the posterior lateral glomeruli .seem to be related ex- 

 clusivety to Jacobson's organ. Perhaps this is true of all the 

 caecilians. 



The path of the olfactory nerve in caecilians from the olfactory 

 lobe to the point of distribution to the nasal organs is worthy 

 of special notice. The olfactory nerves, dorsal and ventral, run, 

 as described above, in tubular passages in the ethmoid bone. 

 When a processus conchoides is formed, the ventral olfactory 

 cpnal lies at the lateral border of a thin shelf-like extension of the 

 ethmoid. The free edge of this shelf, containing the canal, is 

 raised dorsally in such a way as to push in the ventral wall of 

 the nasal chamber, dividing its cavity into medial and lateral 

 portions (figs. 5 to 7, 11, 12; see also Wiedersheim, '79 pi. Ill 

 and IV, figs. 32 to 34, 37 to 40; Sarasins, I.e., pi. XV, fig. 4). 

 Anterior to the point where the nerve begins to leave the bony 

 canal the vomer sends a dorsal extension to form a part of the 

 support of the projecting ridge (figs. 6, 7, vo.) and more anteri- 

 orly still the nasopremaxillary sends a contributing element 

 (fig. 5, nas.-pmx.). Jacobson's organ opens into the lateral part 

 of the nasal chamber (figs. 6, 7, jo.). In Herpele, Caecilia, and 

 Hypogeophis (Wiedersheun) the canal of the ventral olfactory 

 nerve is developed in the base of the nasal septum and no pro- 

 cessus conchoides of the ethmoid occurs. In consequence, the 

 ventral wall of the nasal chamber is concave, not convex, and 

 Jacobson's organ opens into the nasal chamber near its median 

 border (figs. 8, 9, jo.). In Dermophis the ventral olfactorj^ 

 nerve supplies Jacobson's organ and the olfactory epithelium 

 covering the convexity of the ridge on the floor of the olfactory 

 chamber. The dorsal nerve supplies the medial, dorsal, and 

 lateral walls. In Herpele the ventral nerve supplies Jacobson's 

 organ and the epithelium of the floor; the dorsal nerve the medial 

 and lateral walls. In both species the extreme lateral wall is not 

 olfactory-. 



