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Show 10 PROE. W. N. PARKER ON THE [Jan. 16, agree in this respect, and that the left and right nasal chambers communicate by a slit-like passage beneath the septum just behind Jacobson's organ. O n either side of the septum nasi, a rounded ridge can be seen projecting into the nasal cavity ventrally (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 contained (Ja.), while posteriorly it encloses a racemose gland. This, which we may call the " septal gland" (sp.gl.), opens by a large duct into the posterior end of 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 duet (fig. 6, Ja.d.) passes to open into the cavity of the organ l, which does not extend anteriorly to this point, as it does in Ornithorhynchus. 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 ingrowth occurs 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. 8 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 and horseshoe-shaped, owing to the projecting shelf on the outer wall. In Ornithorhynchus 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 Ornithorhynchus: 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 1 For details as regards Jacobson's organ in other mammals compare Herzfeld, P., " Ueb. das Jacobson's Organ des Menschen u. der Saugethiere," Zool. Jahrb., Abth. f. Anat. u. Ontog., Bd. iii. |
