DEVELOPMENT OF THE SKULL OF THE COMMON FOWL. 
781 
The next section (fig. 11) passes through the interorbital fenestra (i.o.f.). Above is 
seen that part of the presphenoid (p.s.) which runs into the perpendicular ethmoid 
anteriorly ; it is only thickened above, and the orbito-sphenoidal regions ( o.s .) are merely 
fibrous. The middle of the section is nothing but fibre — that of the fenestra; and 
below, the lower part of the presphenoid (p.s.) passes insensibly into the basisphenoid 
( b.s .). Here the “rostrum” ( r.b.s .) is thicker, and the palatines (pa.) are cut through 
their thick but narrow pterygoid extremity. Only the lower part of the next two 
sections is given : in fig. 12 the soft fore end of the pterygoids (p.g.) is cut through, showing 
the enclosed cartilaginous pith; in fig. 13 the pterygoids (p.g.) are cut through where 
they interpose a cartilaginous plate between themselves and the “ rostrum ” (r.b.s.). 
But the structure here indicated is better displayed in a section (fig. 14, 16 diameters) 
made through the basisphenoidal cartilage, exactly below the exit of the optic nerves, 
and immediately in front of the anterior clinoid wall. Here the section of the 
coalesced trabeculae has a pyriform outline, the narrow end being upwards ; this is en- 
closed in much fibrous tissue. Imbedded in this stroma is the rostrum (r.b.s.), which is 
here much broader, but less deep. Outside the upturned part of the rostrum there is, 
on each side, a plate of hyaline cartilage (a.p.), then a synovial cavity, then a similar 
plate of cartilage which is formed in the perichondrium of the pterygoid (p.g.) and out- 
side its ectosteal tube. 
This is very different from what obtains in the Lizard and in the Ostrich (First Paper, 
Plate vii. fig. 4, a.p .) : in them the anterior pterygoid processes are direct outgrowths 
of the roots of the trabeculae, and on their ends cartilage remains for articulation ; in 
the Lizard this is very apt to acquire a rudimentary distinctness as a feebly ossified 
epiphysis ; in both the Lizard and the Ostrich a cartilaginous plate appears on the cor- 
responding part of the pterygoid. 
Notwithstanding the different manner in which the basipterygoids of the Ostrich and 
the Lizard are ossified (namely, in the former from the extraneous “ rostrum,” and in the 
latter from the symmetrical basisphenoidal ectostoses), yet, morphologically, they cor- 
respond. 
This dying-out of the cartilaginous shaft of the basipterygoid outgrowth in typical 
birds is very instructive, being an instance of morphological subdivision in a higher type 
of that which is continuous (uncleft) in a lower or more generalized form. 
In the Fowl the “rostrum,” insinuating itself between the basis cranii and the basi- 
pterygoid articular plate, becomes one with the true basis cranii, and, ossifying the inner 
face of the articular plate, leaves the rest soft for articulation with the pterygoid*. 
The relation of the basitemporals to the basisphenoid is shown in section in Plate 
LXXXIII. fig. 4, which displays the postorbital region. In Plate LXXXIY. fig. 1, 
the lower portion of this section is shown, magnified 10 diameters. 
This transversely vertical slice shows that the roots of the trabeculae (tr.) are pyriform 
* I here use, indifferently, Professor Huxlet’s term “ "basipterygoids,” and my older name, “ anterior ptery- 
goid processes.” 
