40 PROF. G. B. HOWES AND MR. H. H. SWINNERTON ON THE 
Somewhat similarly related to the postero-external wall of the sac is a large 
quadrangular cartilage, the extranasal (ex.), and from this four processes arise. ‘The 
two anterior of these (ex. 1 & 2) are united to the ethmoidal bar so as to enclose 
a fenestra (n.f.'). The two posterior are free, and the third (ea. 3), together with 
the posterior half of the parent cartilage, disposed at a sharp angle to the external 
half of this, contributes to the support of the anterior orbital wall, bounding 
ventrally the ethmoidal foramen (f-e.), which transmits the ophthalmic branch of 
the fifth nerve '. 
In addition to these complex nasal supports, there is present at this stage in 
the nasal floor a sheet of procartilage which, in order to complete our terminology, 
we name the subnasal. This, to which we shall return, is wholly independent in 
origin, and by analogy to the extranasal we suspect that this may also arise 
independently. 
The only remaining changes in the chondrocranium are mainly of the nature of 
advancing completion of the parts now described. No new elements are added 
after Stage Q, These perfecting processes, as they may aptly be termed, are most 
conspicuous at Stages R and T, which may accordingly be dealt with independently. 
Stage R.—A very striking feature of this, as compared with the earlier stages, is the 
straightening out of the ethmosphenoidal region, which at Q was downwardly rotated 
(cf. Pl. III. figs. 4 & 8). This straightening process affects most conspicuously the 
median parts (internasal septum), which now appear as if withdrawn under cover 
of the extranasal cartilage (e@., fig. 8). 
Equally striking are changes involving the antorbital and otoccipital regions. 
That taking place in the former is of the nature of extension most markedly dorsal- 
wards of the interorbital septum (s.7.), by continuation of the process of elevation of 
the basal ethmoid already alluded to (antea, p. 39). Under the combined influences 
at work, growth has become more rapid with the ethmosphenoidal than with the 
otosphenoidal plate; and ready proof of this lies in the now upward direction of 
the third otosphenoidal process (os.°, fig. 1), which at Stage Q (os.°, fig. 4) was arched 
and reached the highest point. Of the fenestrae described at Q (which in life are 
closed by membrane, except where they transmit nerves) only one has undergone 
change, viz. that transmitting the fourth cranial nerve (f. 4, fig. 8). This is now 
complicated, having become continuous with the fenestre transmitting the third 
cranial nerve, the jugular vein, and ophthalmic artery—all four being now closed 
by one continuous membranous sheet. It is clear, on comparison with Stage Q, 
that the cartilaginous bridges which originally separated these fenestre (7. ¢., the fifth 
otosphenoidal cartilage and its near neighbours) have been absorbed. 
As an accompaniment of these changes, the small cartilaginous bar bounding at 
' Cf. Osawa, 98%, p. 504, 
