DEVELOPMENT OP THE SKULL IN THE CEOCODILLl. 295 



trabeculse (tr), that thicken again at the coping of the wall, and then spring upwards 

 and outwards to form the sides of the chamber for the fore brain (C^")- These diverging 

 plates are the orbito-sphenoids (o.s) ; they narrow rapidly in front, and end in free 

 points right and left of the olfactory lobes. The double chamber for these lobes (I) is 

 cut across in the next section (fig. 3), and the vertical cartilage at this part is low, for 

 there is a rounded gap in the wall here (PI. LXIX. fig. 7), which is the perpendicular 

 ethmoid (p.e). Eight and left of this low part of wall the postero-inferior part of the 

 olfactory capsule is cut across, and the hinder portion of the inferior turbinal (i.tb) 

 is shown. 



The nest section (PI. LXXI. fig. 2) shows a higher septum (s.n), with the roof, walls, 

 and floor of the nasal capsule ; above, these cartilages are continuous, but, below, the 

 upturned floor («/') is free; the curious tubular inferior turbinal (i.tb) is shown inside 

 the bulging lower wall (9i.w). 



Still further forwards (PI. LXXI. fig. 1) the inferior turbinal is missed, and the 

 sinuous walls are confiuent with the septum both above and below. 



Close behind the alte nasi (PI. LXX. fig. 13) the aliseptals (al.s) form merely two 

 round tubes, their dividing wall (s.n) being very low. But the narial valves, confluent 

 with the olfactory capsule (PI. LXX. figs. 2, 12, uIm), are thin coils of cartilage that 

 belong to the " superficial " category, but early unite with the capsules ; they lie over 

 the prenasal spike {p.n). 



The partial vertical section (PI. LXIX. fig. 7) is more than half the skull ; in another 

 figure (PI. LXX. fig. 9) less than half is shown, and thus the nasal cavity of the right 

 side is laid open. The transverse sections of the half-ripe Alligator (PI. LXVI. 

 figs. 5-10) help us here, as they show the ethmoidal region better. 



The long bulging part in front (PL LXX. fig. 9) is a mere fold of the wall, the 

 next is the "upper turbinal" (u.tb); it, however, is formed merely by a special 

 infolding of the aliethmoidal wall (PI. LXVI. fig. 9, u.tb), which in that section seems 

 to be a distinct cartilage, midway from side to side and from top to bottom, and having 

 its convex face looking inwards. This fold lies in front of the upper part of the 

 oblique "pars plana" (PI. LXVI. fig. 10, p.p) (the lateral ethmoidal antorbital wall), 

 whilst the inferior turbinal (i.tb), which is a single tube behind (PL LXXI. figs. 2, 3), 

 and an imperfect double tube further forwards, lies in a postero-inferior position 

 (PL LXX. fig. 9). This part is very strong directly in front of the pars plana 

 (PL LXXI. fig. 3, i.tb, and PL LXVI. fig. 10, ^.^). 



b. Visceral Arches. 



The lower jaw is now as long as the rest of the skull (PL LXIX. fig. 9), the facet on 

 the quadrate {q.c) being far back, and the angle of the lower jaw well developed. The 

 quadrate {q) is very large ; it occupies most of the side of the hind skull, and is as broad 

 as that part of the basis cranii against which it abuts, 



VOL, XI. — TXRT IX. No. 5. — Octobcr, 1883. 2z 



