8 PROF. W. N. PARKER OK 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, inuer, and upper sides. Bather 

 further back, each Aving gives rise to a curved rod (fig. 5, aln.tb.) 

 (the " ali-nasal turbinal " of W. K. Parker l ), which passes into 

 the valvular process already noticed as extending into the nostril 

 from the inner side, and a turbhial-like 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 naso- 

 palatine 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 (" Kieehwulste ") are more 

 numerous and complicated than in Ornithorhynchus, in which 

 Zuckerkandl describes three only, and he therefore considers 

 Ornithorhynchus to be " anosraatic," its ethmoid being reduced in 



1 Cf. "On the Structure and Development of the Skull in the Pig," Phil. Trans. 

 1874. ! *' 



