112 MR. W. K. PARKER ON THE STRUCTURE AND 
of the bony centres. The als are not ossified up to their root in front, but the 
bone reaches the front of the unfinished basisphenoid bone (b.s.); behind, they overlap 
it. The hollow under the junction of the base and ale is the place where the 
pterygoids clamped the skull (Plate 14, fig. 1); here the alisphenoids are bevelled ; 
beyond that part they are strongly convex, as they grow first outwards, and 
then upwards. All their three free edges are crescentically emarginate ; the notch 
in front forms part of the wide sphenoidal fissure (V1 *.) ; on the outside a suture is seen 
running from the concave edge to the large foramen ovale (V*.). The ale being 
measured fore and aft, is in the middle of the bone, but it comes near the outer 
edge. Here, again, we have that remarkable character of the alisphenoid which 
we have just seen in the Sloth, Pangolins, and in the genus Dasypus (Plate 7, fig. 1), 
but not in Tutusia (Plate 5, fig. 1), where the alisphenoid, freed from the general 
cranial wall of the chondrocranium, is slow in developing—see especially in Manis 
(Plate 11, fig. 1, als.) 
branch over the edge of the ala. Normally, the 3rd branch of the 5th notches this 
hind margin of the ale (see in Tatusia, Plate 5, fig. 1, V*.), the ‘foramen ovale” 
and thus the huge trigeminal nerve sends its hindmost 
being completed afterwards by a postneural bar of bone. But in the Mole (Zalpa 
europea) it perforates the primary cartilage, and the 2nd branch does the same, 
so that in that type the ‘foramen rotundum” is also a primary foramen of the 
chondrocranium, and not a notch completed afterwards by a bony bar.* 
The large outer and hinder lobe of the alisphenoid binds in front of the “ tympanic 
recess” of the squamosal, and then the hind margin rapidly running forwards, this 
bene closes upon that great auditory outgrowth, the cochlea (chl.). Between the 
cochlese the basal beam keeps on widening backwards, behind the bony basisphenoid 
(b.s.). There is a tract of this widening cartilage three-fourths the extent of the bone ; 
behind this the basioccipital is twice as long as the cartilage, and reaches to the front 
(or lower) edge of the foramen magnum (/.7.). 
This latter bone (b.0.) is six-sided, has a straight front margin, a concave side margin 
lying against the convex cochlez, a slightly concave margin followed by cartilage, 
postero-laterally, and its emarginate end is at the foramen magnum. The condyles 
(oc.c.) are short, convex, and ear-shaped ; the small exoccipital bones (e.0.) are close 
in front of them, and end against the hypoglossal (or condyloid) foramen (XII.). The 
fore part of the foramen magnum has the bone and cartilage raised into a protecting 
* If we lose patience over these details we shall miss the best things in this minute morphology. 
In the normal freedom and out-thrust of the Mammalian alisphenoid, and in the very varied manner 
of escape of this inferior maxillary nerve—through, or over, or behind the ale—we have specializations 
that must be compared with the modification of this part of the general cranial wall to be seen in 
Serpents, Lizards, and Tortoises, where what is one continuous growth in Sharks, Frogs, &e., is in 
one case a little patch, in the next a narrow “ upright,” and in the third case, the Chelonian, it has 
suffered complete suppression. (See Trans. Zool. Soc., vol. x., plate 38, fig. 2; Phil. Trans., 1881, 
Plates 1-44; ibid., 1878, Plates 27-83; zbid., 1879, Plates 37-45; and ‘Challenger Reports,’ vol. i., 
Zoology, plates 1-13.) 
