DEVELOPMENT OF THE SKULL IN THE CEOCODILIA. 283 



a deep groove runs down inside between the fore edge of the capsule and the out- 

 turned selvedges of the hooked, overlapping alisphenoid (al.s). In section (PI. LXVII. 

 fig. 8) the auditory capsule is seen to be very distinct, from the wide, swelling plate 

 below — the double parachordal, with the uniting notochord and its ossifying sheath 

 (b.o, iv, nc). 



This section is in front of the supraoccipital cartilage ; it cuts through the falcate 

 otic process {ot.p) of the quadrate and its lower or articular part {q) ; the articular part 

 of the mandible (ar) is seen in situ. Fitting into the fenestra ovalis (fs.o), the columella 

 (in.st) is seen, behind it a narrow tract of cartilage is cut through, and then there is 

 another opening, the fenestra rotunda (f-r). This section is through the mouth of 

 the cochlea, and thus seems to show the two fenestrse as opening into one cavity. The 

 fore part of the sacculus (vi) is cut across above and within, and above it, in the crest 

 of the capsule, the neck of the first ampulla (a.s.c). The columella has its medio- 

 stapedial part (ni.st) ossified, and its extrastapedial end (e.sf) is seen rising outside the 

 otic process of the quadrate. We must look further back for any rudiment of the 

 " tegmen tympani " (PI. LXV. fig. S) ; it exists here merely as the projection of the 

 canals. 



The fenestras in the walls of the skull difier from those in the Bird, and are of less 

 extent than those in the Lizard ; in the former the alisphenoid itself is fenestrate ; 

 here there is a large space between the orbito- and alisphenoids, well margined above 

 by a band which is not found in the Bird ; whilst a smaller band below divides that 

 from another smaller fenestra between the hind part of the orbito-sphenoid and the 

 presphenoid. 



As I have just shown, the alisphenoid, instead of lying far from the auditory capsule, 

 as in the Lizard, clings close to it, here, and is only separated from it by a chink. The 

 postsphenoidal region is cut through in another section (PI. LXVII. fig. 7) just at the 

 back of the pituitary cup (pi/), which is seen to have some "acini" of the "gland" 

 in it. Here the ossification (b.s) has reached the cup (PI. LXV. figs. 6, 7, b.s) ; but 

 the part where the parachordals pass into the prechordals, laterally, is unossified ; here 

 the alisphenoids (al.s) are seen to be direct continuations of the basal (parachordal) 

 plate. Above, the fenestra is cut across at its hind part, and the upper band [u.o.al) is 

 strong and incurved. 



The front angle of the otic process of the quadrate {ot.p) is seen in section, outside 

 and below that band. 



In the next section, through the front of the pituitary cup (PI. LXVII. fig. 6,^y), 

 the apices of the trabeculse {tr) are cut across, close in front of the growing basi- 

 sphenoid bone {b.s). The optic nerves (ii) are severed close below the lower band 

 of cartilage, the lower orbito-alisphenoidal band [l.o.al) ; and above, at some distance, 

 the upper band {u.o.al) is severed, where it is thickening towards its fore part. 



Meckel's cartilage {mk) is seen in section also. In front of the pituitary body 



