DEVELOPMENT OF THE SKULL OF THE COMMON FEOG. 
161 
The relations of these parts are shown in Plate VII. fig. 1 from the side, in fig. 2 from 
above, and in Plate VI. figs. 9 & 10 sectionally, vertically transverse. 
The broad ethmoidal wall, which had as a foundation the trabecular commissure, when 
seen from the front aspect (Plate VI. fig. 9), has this rudimentary “ septum nasi” (s.n.) 
projecting directly from it. 
The cartilage that lies between the olfactory foramina (1) answers to the “ lamina 
perpendicularis ” of the ethmoid ; it is, however, very short and very thick. The lateral 
ethmoidal region, partly cut away in the figure (Plate VI. fig. 9) is curved gently round 
on each side, and passes continuously into the lateral skull-wall (Plate VII. fig. 1, o.s., 
fig. 2, eth.). It also passes into the palatal bar {pa.), at the root of which is the curious 
pterygo-palatine process (Plate VII. fig. 2, p.p.p.), a part well seen in Tadpoles of Bana 
pipiens and Pseudis paradoxa ; in them it has all the appearance of being a rudimentary 
“ antorbital ” or “ pars plana.” 
A section made in front of the ethmoid, but through the growing “ septum ” (Plate VI. 
fig. 10, s.n.), shows the relation of the olfactory passages to the parts that are walling 
them in. 
The trabecular horns [tr.c.) form a convex floor; these are connected by fibrous tissue 
to the partition ; and a dotted line ( al.s .) shows where the cartilaginous roof or aliseptal 
plates will appear. At present they are mere indifferent tissue ; but soon, as the septum 
elongates, a laminar outgrowth of hyaline cartilage will proceed forwards from the ante- 
rior edge of the transverse ethmoidal wall, and outwards from the crest of the septum. 
The optic foramen (Plate VII. fig. 1, 2) and the “ foramen ovale ” (5) are now enclosed in 
cartilage ; in the last stage they were passages in the membranous cranium. 
The pterygo-palatine bar, which in the former stage was a mere bridge connecting the 
quadrate region with the prefrontal, has now acquired a length equal to that of the 
suspensorium ; so that the subocular arch is now V-shaped. 
Meantime the anterior crus of this arch has begun to lose its straight form, and to be 
bent a little forwards at its upper third {pa.) ; here it is partly constricted off : this 
transverse segmentation, although imperfect, marks where the pterygoid {pg.) begins ; 
this latter part is broader than the palatine. 
The metapterygoid root {m.pg.c.) of the mandibular arch is fast diminishing, and has 
begun to cling to the fore part of the ear-capsule, with which it will eventually coalesce. 
The temporal muscle {t.m., indicated by dotted lines) still passes downwards and forwards, 
but much more downwards than before, on the inside of the orbital - process {or.p.); 
but this outgrowth is now much less, has become four-square, and is now beneath and 
behind the eye, not beneath and in front ; it has been brought very near to the auditory 
sacs. 
There is now a very sharp distinction between the supra- and the infrahyomandibular 
{s.h.m., i.h.m.) ; and the upper region has become really as well as relatively less. The 
lower portion has grown into an ear-shaped lobe, scooped on the outside and convex 
within : the base of this lobe is now only half its former distance from the periotic mass. 
MDCCCLXXI. z 
