148 
MR. W. K. PARKER OK THE STRUCTURE AHD 
orbitosphenoids reach their own cartilaginous base (qJ.s.). The well-ossified ali- 
sphenoids ( al.s.) are seen articulating with the wide, extensive basal bone,* which 
shows its pituitary hole in front, and has a low postclinoid ridge running across 
behind the middle, it has, in front of it, a very shallow “ sella.” The hinder part 
of the floor is shown in the partial figure (5) ; but the huge supraoccipital tegmen, 
with its wide, angular ossification ( s.o .) overlapped in front by two interparietals ( ip .), 
are to be seen in the main figure (4). All the canals ( a.s.c ., h.s.c., pi.s.c.) can be seen 
in this view where the large auditory capsules project outwards, like short ears, from the 
sides of this curious cranial “vessel.” The exoccipitals (e.o.) can just be seen rising right 
and left towards the postero-external margin of the supraoccipital osseous centre (s.o.). 
Visceral arches of the Fourth Stage. 
About one-third of Meckel’s cartilage (Plate 22, fig. 7, mk.) is now enclosed in a 
canal formed by the dentary (d). I 11 front of this buried part the cartilage rises and 
swells into a thick mass, up to where it meets its fellow, from which junction the 
basimandibular ( b.mn .) grows forwards, and a little upwards. 
The condyloid mass of cartilage is now much larger than that which still 
remains unossified on the ends of the coronoid and angular processes. The parts 
that form the ossicula (ml., i., st.) have merely become enlarged without any 
noticeable change ; the annulus ( a.ty.) is also increasing in size. 
Fifth Stage.—Skull of Erinaceus europaeus ; 1 month old; head lk inch long. 
a. Investing bones .—The superficial parts of the skull have been worked out and 
figured in this stage (Plate 20, figs. 1-3), as in the second (Plate 17, figs. 3-5), 
and in the sub-adult (Plate 21, figs. 1-6). 
In the upper view (Plate 20, fig. 2) we see what a strong roof the investing bones 
now form to the very solid endocranium. The nasals (n.) are small, narrow bones, 
and diverge in front; the frontals (f) are almost as large as the parietals (p .); they 
are now in one piece on each side. 
The large convex parietals have the frontals running in between them in the coronal 
suture, and the double interparietal (i.p.) fits on to them concave hinder margin. 
The sides of the hind skull are well buttressed by the squamosals (sq .), and the fore 
part of the skull by the huge maxillaries (mx.), and the middle-sized premaxillaries 
(px.); the jugals (j.) are smallish ; the lachrymals are not well seen in this view. 
But in the side view (Plate 20, fig. 3) the lachrymals (/.) are seen to be intraorbital; 
they are oval, have a large opening ( l.c.) in front, and are very thin. The imbrication 
of the subcutaneous scutes that invest the endocranium is well seen in this view. 
The jugal was removed in the preparation figured, to display the interior of the orbit, 
the inner wall of which is composed of the lachrymal, orbital plate of the frontal, and 
maxillary, in front; and behind, by the frontal, parietal, and squamosal; it is a very 
* Eor 6.0. read b.s. 
