10 PB.OF. W. ]S\ PAIIKEE OX THE [Jan. 16, 



agree in tbis respect, and that the left and right nasal chambers 

 communicate by a slit-like passage beneath the septum just behind 

 Jacobson's organ. 



On either side of the septum nasi, a rounded ridge can be seen 

 projecting into tlie nasal cavity ventraJly (figs. 5-11 and 14-16), 

 beginning close to its anterior end and passing right back into 

 the ethmoidal region, where it is eventually continuous with the 

 partition separating the nasal chamber from the posterior nares. 

 Within the anterior part of this ridge Jacobson's organ is con- 

 tained {Ja.), while posteriorly it encloses a racemose gland. This, 

 which we may call the "septal gland" (s^j.gl.), opens by a 

 large duct into the posterior end o'i Jacobson's organ and by a 

 number of others into the nasal cavity along the anterior part of 

 the ridge, one extending even in front of Jacobson's organ (fig. 5), 

 The anterior part of the ridge was noticed by Zuckerkandl, but he 

 says no more about it. In fig. 3 the part behind Jacobson's organ 

 is removed, so as to show the turbinals. 



As already mentioned, Jacobson's cartilage forms a large and 

 independent tube, into the anterior end of which an offshoot from 

 the naso-palatine duct (fig. 6, Ja.d.) passes to open into the cavity 

 of the organ \ which does not extend anteriorly to this point, as it 

 does in OrnithorJiynchus. In other words, Stenson's duct is situated 

 further from the end of the snout in the latter animal, so that 

 Jacobson's organ does not extend so much beyond it posteriorly as 

 in Echidna. From the outer side of the tube an ingrov^th occnrs 

 so as to form a sort of shelf or turbinal cartilage along the greater 

 part of its length (figs. 7, 14, and 16). This disappears posteriorly, 

 and the tube itself ends about opposite the anterior extremity of 

 the maxillary turbinal (figs. S and 9), in which region sections 

 show a solid piece of cartilage, representing part of the wall of the 

 tube, as well as the mass of nerves and duct of the septal gland 

 which plug the end of the tube. 



Passing now to the organ itself, it will be seen, by a glance at 

 figs. 7, 14, and 16, that the lumen is narrow p,nd horseshoe- 

 shaped, owing to the projecting shelf on the outer wall. In 

 Ornithorhynclius this " Jacobson's turbinal '' is distinctly coiled 

 towards the ventral side, and the cartilage follows the curve 

 (fig. 17), so that if straightened out it would more than reach to 

 the opposite wall of the organ. In Echidna the shelf extends 

 almost straight across the organ, leaving a narrow lumen between 

 it and the wall, and the supporting cartilage only passes about 

 halfway along the shelf. In this respect the Jacobson's organ 

 of Echidna may be said to be less highly developed than that of 

 OrnithorJiynchus : moreover in the young of the latter it is 

 relatively slightly larger than in the adult and than in the young 

 Echidna. 



A sensory epithelium lines the concave margin of the lumen, and 



' For details as regards Jacobson's organ in other mammals compare 

 Herzfeld, P., " Ueb. das Jacobson's Organ des Menschen u. der Siiugethiere," 

 Zool. Jalirb., Abth. f. Anat. ii, Ontog., Bd. iii. 



