304 



ME. W. K. PAEKEE ON THE STEC7 CTUEE AND 



own direction is backwards. Further back (fig. 4) the septum is increasing in height, 

 and the retral processes of the trabecular horns are now much smaller ; these slender 

 laminae I propose to call the "recurrent cartilages"*. 



In ihe fifth and sixth sections (figs. 5, 6, 6") there is no longer any distinction between 

 the rudimentary prenasal cartilage and the completely fused portion of the trabecular 

 bar, the lower part of the septum nasi ; but as this bud-like wedge of cartilage (see 

 Second Stage, Plate XXX. fig. 1, p.n.) never becomes vertical, having its apex downwards 

 as in the Chelonians, still less protruded forwards as in its large counterpart in the 

 Bird, the bony plates that appear as its splints are not superior as in the Bird, nor 

 anterior as in the Chelonian, but inferior. These plates are the premaxillaries, which 

 appear in the Mammal below the snout (see also Callendek, Philosophical Transactions, 

 1869, p. 166, Plate xiv. fig. 6, c, for its inferior position in Man). Yet in the Mammal 

 the premaxillaries are related, as splints, more to the retral trabecular cornua themselves 

 than to the arrested azygous cartilage impacted between them. So much of the alinasal 

 cartilages as are depicted in the enlarged figure (fig. 6", al.n.) is a separate segment — 

 the " appendix alse nasi." The next section (fig. 7) is behind the first third of the septum 

 nasi, where the rudiments of the "hard palate" begin in front, the lips of which appear 

 now on each of the padded bases of the septum, but are here far apart. The long 

 cushion-like valvular mass in which the aliseptal folds (al.s.) end and dilate is the early 

 form of the inferior turbinal, which is not so sharply separate from the alinasal turbinal 

 {al. th.) as in the Bird. A sharp process of mucous membrane is seen above this on each 

 side, where the aliseptal cartilages bend inward ; this is the rudiment of the " nasal 

 turbinal" (see Huxley, 'Elem. Comp. Anat.' p. 248), which is but feebly developed in 

 the Pig. In the thick mass which envelops the base of the septum two flat straps of 

 cartilage are seen in section; these are the "recurrent laminae" {r.c.c), and they are con- 

 tinued in this stage back to that part of the septum which, ossifying earlier than that in 

 front, gets the name of " perpendicular ethmoid" (see fig. 11). On each side of the lower 

 palatal lip there is a rudimentary tooth-pulp shown in section ; and above this, up to the 

 nasal roof, the tissue is marked ofif from the skin and subcutaneous tissue ; this is the 

 granular nidus for the posterior margin of the premaxillary and the anterior margin of 

 the maxillary. The detached piece of this section (fig. 7") is the fore end of the lower 

 jaw with tooth-pulps appearing, and with a curious result of the great prognathism of 

 the type, namely, complete fusion of the ends of the primordial mandibular rods — 

 " Meckel's cartilages (m^.c.)." A section made near the middle of the septum (fig. 8), 

 although answering on the whole to the 7th, shows the tip of the vomer {v.) and a very 

 near approach of the lips of the hard palate, and, below (fig. 8"), the convergence of 

 the mandibular rods and the fore end of a bony tract outside chem ; this is the dentary 

 the tongue [tg.) is here cut across. 



The ninth section (fig. 9) takes in part of the frontal wall, with the foremost part of 



* The "recurrent cartilages" are of great morphological importance; in future communications I hope to 

 show their form and meaning in the Ophidians and in ]jirds, " Tasserines," " Hemipods," the llhea, &c. 



