466 
MR, W. K. PARKER ON THE DEVELOPMENT 
(%. 2, vb.) largely swells the vestibular region ; the form of this cavity is a short oval 
(figs. 2 and 3, vb.). The condition of the hind skull is best studied from above, in a 
preparation of the base (fig. 3) ; here the exoccipitals (e.o.) are seen to be forming 
broad borders of bone to the cartilage of the arch, and these are approaching the 
cephalostyle (basioccipital, b.o.). 
Further forwards, in the angle between the capsule and the basal plate, under 
the Gasserian ganglion, the cartilage is being ossified as a prootic ( pr.o .), and the wider 
wings which stand out from the front of the capsule are becoming the sphenotics 
(sp.o.). Also, still further forwards, the lower wings or basipterygoids (b.pg.) are 
getting a coating of bone; this ectostosis runs upwards into the side wall, in front of 
the capsule—it is the alisphenoid ( al.s.). 
In front of these last wings the trabeculae (tr.) become bent, first outwards and then 
inwards, ready to join the median bar ( i.tr .). They are rounded, solid rods. The 
basal fontanelle is now divided across, near its hinder end, by a narrow band, which is 
cartilaginous at its roots and fibrous in the middle ; this is the late and feeble “ post- 
pituitary wall” ( p.cl .)—here a mere bridge. 
The small triangular space behind is the posterior basi-cranial fontanelle ( p.b.c.f.) ; 
the large, pinched, pyriform space in front is the pituitary space (py.) or anterior basi¬ 
cranial fontanelle. Its narrow anterior third runs up to the intertrabecula {i.tr.), 
which goes further back than the ethmoidal wall ( l.eth -), and is, indeed, the rudi¬ 
ment of the “ perpendicular ethmoid.” Infero-laterally, the ethmoidal wall (Plate 34, 
fig. 2) is very restricted, for the orbito-sphenoidal fenestral (os.f.) is of great length, 
being extended equally in front of and behind the optic nerve (II.). But above 
(fig. 1, t.cr.) the tegmen cranii, in front, is as large as the long oval fontanella ( fo .) ; 
behind that space the spheno-occipital tegmen is one-half longer, axially, and twice as 
wide across. 
The three confluent trabecular bars combine to close in the fore part of the cranial 
cavity (Plate 34, figs. 1 and 3), only leaving an opening right and left for the long olfactory 
nerves (I.). When they have escaped from the skull they lie for the hinder half of 
their course in a deep rounded sulcus between the cornual extensions of the trabeculae 
(i c.tr.) and the huge middle bar {i.tr.). The three bars are at first nearly of the same 
width ; the cornua are rounded where they first project as longitudinal wings, but they 
soon become narrow rods, and end in a pointed manner behind the middle of the pre- 
cranial region. Thence the intertrabecula is a gently compressed rod, only slowly 
lessening forwards, and ending as a slightly winged lobe in the end of the beak. 
The first and second visceral arches (Plate 34, fig. 4) are elongated forwards like 
the skull, but the “ pier v of the hyoid arch (hm., sy.) is less than half the size now of the 
mandibular suspensorium ( p.pg. , pd.). I have shown these with their splints attached as 
seen from above (Plate 34, fig. l) and from below (fig. 2); also without the “ parostoses ” 
from their inner side (fig. 4). Their intrinsic bony centres or “ ectostoses ” are now 
clearly seen, but they are very small in proportion to the cartilage in which they 
