82 MR. W. K. PARKER ON THE STRUCTURE AND 
already spoken of its nasal or olfactory territories. The hind part of the perpendicular 
ethmoid (p.e.), and all the rest of the basis cranii, is displayed ; but the edges of the 
bar, in front, are hidden by the inbent palatines ; just in front of their middle, the 
presphenoid (p.s.) begins, and this is halfway, exactly, between the end of the snout 
and the front edge of the foramen magnum (fim.). If the postelinoid wall could be 
seen, it would be found to be half way from the end of the former to the foramen 
magnum ; the open pituitary space ( py.) is a little in front of it. 
A little in front of that primary opening, the basicranial beam is composed of three 
bars melted into one; the lateral bars are the trabeculee, and they end between the 
widest parts of the ethmoidal swellings and the middle of the vomer; thence the 
basiseptal mass is formed of the azygous intertrabecula, 
The orbitosphenoids are trabecular crests, as the great internasal partition is an 
upgrowth of the intertrabecula. 
In the Crocodile and Alligator (see Trans. Zool. Soc., vol. 11, plate 64, fig. 2, 
tr’., 0.8.) the orbitosphenoids, are seen growing directly upwards and outwards, from the 
paired trabecule. After the great intertrabecular crest is well developed, and the 
trabeculee become thinned out on its sides, right and left, some transverse sections 
show a discontinuity between the orbitosphenoids, perched at the top of the crest, 
and the flattened trabeculz from which they sprung (7bid., plate 67, figs. 2, 3). 
In Serpents (Phil. Trans., 1878, Plates 28-31) there is no intertrabecula, and 
the nasal roofs dip down, and coalesce with the trabeculee, which become fused in the 
internasal region. But in the interorbital region the trabeculze persist as free terete 
rods of cartilage, and both the orbitosphenoids and alisphenoids arise in the wall of 
the membrano-cranium as small, free patches of cartilage. This is a curiously 
abortive and arrested condition of these parts. 
Here in this little skull, which is abortively developed, both within and without, the 
very feeble orbitosphenoids, small and with very imperfect angular extensions, 
above (compare figs. 1 and 3 with the skull of the embryo of Tatusia, Plate 2, fig. 1), 
are articulated to, or distinct from, the proximal part, ending above it in a bilobate 
process. There is, however, evidence here that this is the abortive development of a 
type above the Marsupials, for the optic nerve (TI.) passes through a ring of cartilage, 
and not through a common optico-sphenoidal fissure, as in them. 
The rest of the sphenoid, excluding the abortively developed orbitosphenoids, is a 
remarkable structure. The basal beam is very wide, and has, for a Mammal, an 
unusually large and almost Sauropsidan pituitary hole; opposite that unfinished 
space the base grows out into a pair of thick rounded ears of cartilage, thicker and a 
little wider than the lateral processes of the presphenoid, which are perforated for the 
optic nerve. A rounded notch is seen both in front of and behind these small auriform 
alisphenoids (a/.s.), and these notches are actual foramina, through the membrano- 
eranium ; the foremost is the sphenoidal fissure (V*.), and the hinder is the foramen 
ovale (V®.), only a foramen as it respects the membrane, not the cartilage. But the 
