12 
MR. W. K. PARKER ON THE STRUCTURE AND 
or free, outstanding wing, not of cartilage now, but of bone. This fan-shaped tract 
has its broad part ossified separately, from the lower part or stem (see fig. 6, al.s.).* 
At a distance from the basioccipital equal to the width of both the basal and lateral 
bony centres, the exoccipitals (e o.) have appeared, they form part of the selvedge 
round the foramen magnum. Above another equally large space of cartilage we see 
the supraoccipital ( s.o .): it has a right and left half (see also fig. 6, s o .); each half is 
ear-shaped, the broad end being near the mid-line. 
A considerable fossa runs between the occipital arch and the auditory capsule ; this 
is occupied by the “lateral sinus ” ( s . c.), which communicates with the outer veins 
through a large hole, both above and below. 
The foramina for the postauditory nerves are seen in this view ; that for the 
hypoglossal (XII.) in the middle of the space between the exoccipital and basi¬ 
occipital, and the double space for the vagus and glossopharyngeal (X., IX.) in the 
interspace or fissure between the auditory capsule and the front side of the occipital 
arch. 
The multiperforate “meatus internus ” for the 7th and 8 th nerves (VII., VIII.) has, 
beneath and in front of it, the projecting cochlea (chi.); and above it the arches of the 
anterior and posterior semicircular canals (a.s.c., p.s.c.), meeting in one common sinus ; 
these can be seen shining through the cartilage. 
The lower alisphenoidal centre is deeply notched (above b.s.) to form an imperfect 
foramen ovale (V 3 .) for the third branch of the trigeminal; the second and first 
branches (V 1, ~.) escape through the sphenoidal fissure—between the bulging 
alisphenoid and the concave posterior margin of the stem of the huge orbitosphenoid 
(o..s.). The lesser cranial nerves (3rd, 4th, 6th) escape also through this space, but the 
optic foramen (II.) is an oval hole pierced through the orbitosphenoidal stem. No 
part of the anterior sphenoid is ossified at present, nor any part of the nasal region. 
The turbinal outgrowths of the proper olfactory region shown by the slicing away 
of the cartilage (fig. 5, u.th.) are very numerous ; above and behind them, in the huge 
recesses for the olfactory lobes, the numerous branches of the 1st nerve are seen to be 
escaping through a membranous floor, which is having bands of cartilage formed in it 
( cr.p .), that pass round the various fissures through which the nervous bands escape. 
The cartilage of the roof of the nasal labyrinth is shown in the main figure (fig. l) 
as cut away from the large partition wall. In front, the alinasal region, behind the 
opening and near the mid-line, gives off a curious “recurrent cartilage'’ ( rc.c .) of a 
lanceolate shape, and scooped along the outside, except in front, where it forms a tube. 
These cartilages (right and left) protect “ Jacobson’s organs,” which are partly 
encapsuled by them ; these parts are related to two small bones and to the vomer, as 
I shall show soou. In the figure of this vertical section the frontals and parietals 
( f.p .) are shown, helping to fill in the great fontanelle; the nasals ( n .) are seen over 
* In Birds, generally, and in many Rodents, the alisphenoid is formed from two osseons centres, but 
in a manner very different to what is shown here. 
