158 
GENERAL OBNITHOLOGY. 
sloping with less distinction in front toward the orbital cavity. In this auditory hollow may be 
seen several openings : the meatus or proper ear-passage, through which, in one direction, a 
bristle may be passed to emerge at or near 
the middle line of the base of the skull, 
about the root of the basisphenoidal ros- 
trum. Such a passage is through the first 
visceral cleft of the early embryo, modi- 
fied into meatus auditorius and eustachian 
tube, which latter communicates with the 
back part of the mouth. Besides the other 
ear-passages proper, may be found other 
openings of air-passages leading into the 
interior diploic tissue of bones of the 
skull, and especially into the lower jaw 
bone. The ear-parts are immensely de- 
veloped in owls, in many species of 
which they are unsymmetrical, that is, 
not sized and shaped alike on right and 
left sides of the head. 
The Sphenoid (Gr. a4>riv, sphen, a 
wedge ; eldos, eidos, form ; figs. 62, 70, 
71) is a compound bone, not easy to un- 
derstand as it occurs in birds, as much 
of it is hidden fi-om the outside, some of 
it is very slightly developed, and all of it 
is completely consolidated with surround- 
ing bones in the adult. It is wedged 
into the very midst of the cranial bones 
proper, with its body in the middle line 
below, next in front of the basioccipital, 
and its wings spread on either side in the 
orbital cavity. A sphenoid consists es- 
sentially of the basisphenoid, or main 
part of the bone (fig. 62); the alisphe- 
mids or ^' wings," on either side (figs. 70, 
71, as) ; the obscure presphenoid, (ps) in 
the middle line in front of and above the 
main body ; and the small orbito-sphe- 
noids. which are in fact the wings of the 
presphenoid. The body is usually covered 
in by the underflooring of the basitem- 
poral ; it is a flat triangular plate, pro- 
duced more or less forward in the middle 
line as the basisphenoidal rostrum, or 
beak of the skull. This rostrum is an 
important thing. It forms, in fact, the 
central axis of the base of the skull; 
with the mesethmoid plate the inferior 
border of the interorbital septum, usually 
Fig. 70. — Ripe chick's skull, longitudinal section, viewed 
inside, x 3 diameters ; after Parker. In the mandible are seen : 
mk, remains of meckelian rod; d, dentary bone; sp, splenial ; 
a, angular ; s?f, surangular ; ar, articular ; iap, internal articu- 
lar process; jjap, posterior articular process. In the skull: pn, 
the original prenasal cartilage, upon which is moulded the pre- 
maxillary, px, with its nasal process, 7ipx, and dentary process, 
dpx ; sn, septo-nasal cartilage, in which is seen nn, nasal nerve ; 
ntb, nasal turbinal ; the reference line crosses the cranio-facial 
suture, the face parts and cranial parts being nearly separated 
here by the nick seen in the original cartilaginous plate; eth, 
ethmoid ; pe, perpendicular plate of ethmoid, which will spread 
nearly throiaghout the dotted cartilaginous tract in which it lies, 
to form nearly all the interorbital septum ; transverse thicken- 
ing (in some birds) below the reference line eth will form the 
pre-frontal, or orbito-nasal septum ; iof, inter-orbital foramen ; 
ps, pre-sphenoidal region, just above which is the orbito-sphe- 
noidal region ; 2, optic foramen ; as, alisplienoid, with 5, foramen 
for divisions of the 5th ( trifacial) nerve ; /, frontal ; sq, squamosal ; 
^9, parietal; «o, superoccipital ; asc, anterior semicircular canal ; 
sc, a sinus (venous canal); ep, epiotic; eo, exoccipital; op, opis- 
thotic ; po, prootic, with 7, meatus auditorius internus, for en- 
trance of 7th nerve ; 8, foramen for vagus nerve ; ho, basioccipi- 
tal ; ht, basitemporal ; ic, canal (in original pituitary space ; 
fig. 66 ic) by which carotid artery enters brain cavity ; ap, basi- 
pterygoid process; ap to rhs, rostrum of the skull, being the 
parasphenoid bone underflooring the basisphenoid and future 
perpendicular plate of ethmoid. (The scaffolding of the upper 
jaw not shown, excepting ^x, &c.) 
