OCR Text |
Show 8 PROE. W. N. PARKER ON THE [Jan. 16, Ornithorhynchus. The thick and solid septum nasi, which is rounded off below, gives rise to two lateral ali-nasal wings (aln.) above, and these extend anteriorly beyond the septum and support the external nostrils on the anterior, inner, and upper sides. Rather further back, each wing gives rise to a curved rod (fig. 5, aln.tb,) (the " ali-nasal turbinal" of W . K. Parker 1), which passes into the valvular process already noticed as extending into the nostril from the inner side, and a turbinal-]ike ridge is thus formed from the roof of the anterior part of the nasal cavity-this ends anteriorly to the " maxillo-turbinal." In Stage II. the ridge supports a very complete valve, which can probably close the aperture of the nostril completely (fig. 13). It will thus be seen that there are no transverse connective-tissue septa in the front part of the nose as in Ornithorhynchus. Posteriorly to the nostril, the two wings gradually extend further downwards, so as to form an outer projecting wall to the nasal chambers, and a short distance behind the naso-palatine ducts they are continuous ventrally with the partial cartilaginous floor, which supports about the outer half of the anterior part of the nasal cavities (figs. 7-11, and 14, Plates II. & III.). The lower side of the snout, below the nostrils, is supported by a large transverse rostral cartilage (figs. 4-6 and 13, rs.), continuous dorsally with the two ali-nasal wings in front of the nostril and also with the septum nasi. This cartilage becomes constricted off from the septum slightly in front of the naso-palatine canals, and then forms an independent plate on either side, the swollen internal margins of which abut against the base of the septum (fig. 5). This thickened edge is separated off from the rest of the plate as a club-shaped mass in the region of the naso-palatine duct, which passes between the two portions. The inner club-shaped portion then becomes hollowed out on the external side, where Jacobson's duct enters its cavity as an offshoot from the nasopalatine canal, and the cartilage then forms a complete independent tube, enclosing Jacobson's organ (figs. 6-8, 14 and 16). The lateral part of the cartilaginous nasal floor sends up a process on the dorsal side (fig. 6), which soon meets with the roofing cartilage (figs. 7-9 and 14) ; a small plate becoming separated off from its inner edge (fig. 7), which then meets with its fellow to form a median plate lying beneath the two Jacobson's organs (figs. 14 and 16), and gradually fades off into a median and two lateral backwardly directed processes which end beneath the posterior part of Jacobson's organ. In the young Ornithorhynchus the nasal capsule is simpler and forms a more complete box (fig. 17). Even in the older stage, none of the turbinals have begun to ossify. The ethmoid turbinals (" Riechwiilste ") are more numerous and complicated than in Ornithorhynchus, in which Zuckerkandl describes three only, and he therefore considers Ornithorhynchus to be " anosmatic," its ethmoid being reduced in 1 Cf. "On the Structure and Development of the Skull in the Pig," Phil. Trans. |