86 PROF. W. K. PARKER ON THE STEUCTUEE OF 



is a double pouch. The front division opens outwards as the outer nostril, and the 

 hinder into the inner nostril, outside the ascending submesial process of the palatine 

 bone (see also Plate XVI. fig. 2, pa, i. n). 



In the transverse sections through and in front of the outer nostril (Plate XVIII. 

 figs. 2-5), we see how the cornua trabeculse {c. tr) form the dilated floor, and that to 

 these horns are added the growths of the annular alinasal (al.n). 



Directly behind the nostrils (fig. 5) the septum nasi (s. m) is seen to be definitely rounded 

 below, a form which it keeps as it passes backwards as the septum also of the orbits 

 (the perpendicular ethmoid and presphenoid — p.e, p.s). 



At the widest part of the nasal pouch, through the middle of the hinder division, we 

 see that the aliseptal cartilage (Plate XVIII. figs. 6 & 6a, a/.sj)) becomes both wall and 

 floor (n. w, n.f) as well as roof. The floor is dilated where it presses against the intruded 

 upper palatine process {pa) on each side; and near this part the cartilage grows 

 inwards so as to form a semicircle (half a coil) with the outer part of the floor ; this 

 half-coil is the " inferior turbinal " (/. th). Where the wall turns inwards, below, to form 

 the floor, there, on the outside, a large pedate process of cartilage grows downwards and 

 inwards ; this is the ethmo-palatine cartilage {e.pa), which generally becomes confluent 

 with the nasal pouch even in the Urodela ; it is very large in the Chameleon. 



Behind the nasal pouches and the hinder part of the ethmoidal roof the perpendi- 

 cular ethmoid (Plate XVIII. fig. 7, al.e, p. e) is still no deeper than the septum nasi 

 (fig. 6, s.n); but it is much thicker, and the top of it is grooved, and in the groove run 

 the olfactory nerves (i). The next section (fig. 8) shows a similar structure ; but in front 

 of the interorbital fenestra the cartilage, now presphenoid (fig. ^, p.s), is of considerable 

 depth and is becoming thin in the middle. The next section (fig. 10) is through the 

 common optic foramen (ii.) ; and now the cranial cavity is suddenly widened to receive 

 the fore part of the hemispheres. 



The next two sections (figs. 11 & 12) are through the alisphenoidal region, and where 

 the mid brain lies ; the cavity of the skull is here at its widest. The first of them is 

 close in front of, and the next directly behind, the " sella turcica." In the first (fig. 11) 

 the alisphenoids {aJ.s) are cut through where they are seen to rest on the basisphenoid 

 (h.s), which is deeply scooped above for the pituitary body {py), and below shows the 

 beginning of the basipterygoid wings {hpg). 



The partly ossified anterior part of the supraoccipital (s.o) is shown in the next 

 section (fig. 12) ; here the sides are membranous, and through a hole in this large 

 fenestra, below, the trigeminal nerve (v.) is seen emerging. The prootic (pro) passes 

 forward under the foramen ovale, and articulates with the broader part of the basi- 

 sphenoid {h.s), which is subconcave above and winged below {b.pg). 



In the next section (Plate XVII. fig. 5) the supraoccipital [s.o) is seen as a thickish 

 vertical plate under the interparietal (i.p) ; the notch between this part and the epiotic 

 {ep) is cut through (see figs. 1, 3, & 4). Here the arch of the anterior canal {a. s.c) 



