DEVELOPJIENT OF THE SKULL IN TKE CEOCODILIA. 269 



thirds the length in the first stage (fig. 2), and it will be relatively much shorter than 

 now. Although it appears to be straight in this aspect, it is really bent forwards near 

 the end, and hooked downwards at the end (figs. 7, 8, nc), where it is slightly bulbous. 

 This is like what I found in the same stage in Chelone viridis {op. cit. pi. 2. fig. 4). 



The parachordal cartilage grows up into the recess under the mid brain (C-) much 

 further than the notochord, so that, already, that rod has retreated from its first position 

 between the moieties of the investing mesoblast; the ascending plate of cartilage is the 

 " posterior clinoid wall '' (p.cl.), a partwhich is developed much more in the Sauropsida 

 than in the Ichthyopsida. 



The folding over of the notochord at its end is the counterpart, in the skeleton, of 

 the folding over of the mid brain ; both the fore skull and the fore brain appear to be 

 outgroivths from the proper end of the skeletal and neural axes; the arrest of the 

 hypoblast at this point favours such a view ; this view would also put the optic and 

 olfactory nerves out of the normal category'. 



The parachordal plate, which is still distinct from the auditory capsules, has very 

 sinuous outlines, for it is pinched in by the pressure of those capsules and by the 

 cranial nerves. 



Behind (PI. LXIII. figs. 4, 6, oc.c, iv) the occipital condyles are being formed, and 

 the plate of cartilage in front of them is pierced by the hypoglossal nerves (xii), and 

 notched by the glosso-pharyngeal and vagus nerves (ix, x). 



Also the growth of the cochleae {chl) towards the mid line causes the parachordals 

 to become very narrow, thence they widen out and get in front of the auditory capsules 

 (aw), and at this, their widest part, they are notched by the large Gasserian ganglia (v). 



As seen from below (fig. 4, iv) these plates seem to end in the postpituitary region, 

 on this lower plane ; but the upper view (fig. 6) and the sections (figs. 7, 8) correct 

 this view. 



The two plates ascend under the hind brain (C') into the large space within the 

 folded mid brain (C"), and grow, right and left, into large wings ; these wings are the 

 alisphenoids [al.s) ; they grow from the " posterior clinoid wall " [p. cl). The base of 

 each wing grows round the fore edge of the hind skull, and the tip of each touches 

 the hind corner of the adze-shaped orbito-sphenoid [o.s) ; the upper surface of these 

 wings is sinuous, and fits to the swellings of the overlying membrano-cranium. 



The basal plate looks outward, right and left, at the fore end, and is notched (for the 

 notochord, nc) in the middle. Between these points the trabeculee {tr) arise ; they are 

 very thick, short, pointed " horns," curving towards each other, but kept apart in front 

 by the thick intertrabecular bar (figs. 4-6, i.tr). Above (fig. 6) the trabeculae lie on 



' The reader will observe, if he compares this with former papers of mine, that my views are becoming more 

 and more in harmony with those of Prof. Huxley and ilr. Balfour. The truth of the matter is this, that I 

 am gradually placing my work on an accurate emhryological basis. 



