DEVELOPMENT OF THE SKULL OF THE COMMON FEOG. 
165 
The bony plates which arise in the perichondrium on the inside of the suspensorium 
and pterygoid bar can now be well seen. In the side view (Plate VII. fig. 5 ,p.g.) the 
pterygoid can be seen mounting above the edge of the bar ; but it is best seen from 
within (Plate VIII. figs. 2 & 4, p.g.) ; it is a very delicate tract, much like a few threads 
of the skeleton of a Siliceous Sponge (fig. 4). 
In front the bony pterygoid is a mere needle ; but it expands at the root of the bar, then 
contracts, and expands once more above. The upper portion is semidistinct from the 
lower ; it is quite distinct afterwards. Behind the metapterygoid bar another ectosteal 
plate has appeared, taking the form of and closely embracing the inner or convex face 
of the “ infrahyomandibular this plate of bone (Plate VIII. figs. 2 & 4 answers 
to the inner face of the lower half of the ichthyic hyomandibular (see PIuxley’s Elem. 
p. 176, fig. 71, HM.). At present there is no bony palatal on the anterior part of the 
subocular arch ; but at its keystone there is a small style (Plate VIII. figs. 1,2, 3, 4, qu .) ; 
this lies on the outside of the quadrate condyle, and projects forward ; it is the ectosteal 
plate of the quadrate sending forward a quadrato-jugal process. 
Two other bones have now appeared on each side, embracing the fifth and the eighth 
nerves: the foremost of them is the prootic (pro.); and the other is the exoccipital 
( e.o .). These patches lie principally on the underside (Plate VIII. figs. 2 & 4, pro., eo.), 
but they are also lateral (Plate VII. fig. 5, pro., eo.). 
They do not commence in the perichondrium, but in the superficial cells of the carti- 
laginous cranium (“ superficial endostosis ”) ; but, unlike endosteal tracts hereafter deve- 
loped, they ossify the cartilage throughout. Each tract is sickle-shaped ; the prootic 
commences external to the nerve outlet, soon to embrace it ; the exoccipital begins on 
the inner side. Now also can be seen a pair of fibrous bones, which never, I believe, 
graft themselves on cartilage or take on an ectosteal character ; these are the “ vomers” 
(Plate VIII. fig. 2, v.). They are, at this stage, little spicular radiating tracts of ossified 
fibre, lying somewhat mesiad of the inner nares. The great basicranial splint, the para- 
sphenoid (Plate VIII. fig. 2 ,pa.s.), has now become cross-shaped by acquiring basitem- 
poral icings ; in front it reaches to between the palatal roots in the prefrontal region ; 
behind it nearly reaches to the end of the basioccipital region ; and on each side its wings 
almost touch the edge of the “ fenestra ovalis.” This bone is convex and subcarinate 
below, and scooped above, where it undergirds the basis cranii. The dentary and the 
articulare are both easily separable from the cartilage (Plate VII. figs. 5, d., ar., m.Jc.); 
they are fast increasing in size and density. 
The relation of the membrane-bones to the cartilaginous cranium is well seen in sec- 
tions. The parasphenoicl is seen as cut through at various points in Plate VII. figs. 7-10, 
pa.s ., the frontals in figs. 7-9, f., the parietals in fig. 10, f., the nasals and vomers in fig. 
6, n., v. They are so delicate at first, and so closely in contact with the face of the carti- 
lage, that here at least the parosteal tracts have nothing to distinguish them from the 
ectosteal. From the rudimentary condition of the bony tracts it results that as yet the 
