156 
GENERAL OBNITHOLOGY. 
whole forming an outer lateral rod from quadrate to premaxillary, like a duplicate of the 
pterygo -palatine rod from the same to the same. 
Among occurrences of later stages are to be noted the development in membrane in the 
middle line below of the vomer, borne upon the end of the rostrum ; the roofing in of the 
wliole skull by the parietal, squamosal, frontal and nasal bones ; the completion of the periotic 
hones as the prootic, epiotic and opisthotic, which form the otic capsule ; the development of 
lacrymal hones, bounding the orbits of the eyes in front. Absorption of the middle wall of 
cartilage between the nasal and orbital cavities nicks off the nose parts from those of the orbit 
(fig. 70, between nth and eth) ; and certain changes in the orbital septum develop the orhito- 
sphenoids. Very nearly all the bones of a bird's skull having thus been accounted for, we may 
next consider them in their adult condition. Keference should now be made to figs. 62, 
63, 70, 71. 
The Occipital Bone (fig. 62, 70, 71) fonns the back part of the floor of the skull, and lower 
part of the back wall of the skull ; neither its boundaries nor its composition is visible in 
adult skulls. It is formed by the hasioccipital, ho, below in the middle line the supra-occipital 
so, above in the middle line ; the exoccipital, eo, on either side. These bound the foramen 
magnum (fig. 69, fm), where the nerve mass makes its exit from the cavity of the cranium into 
the tube of the spina] column. At the lower part of the foramen is the protuberant occipital 
condyle (figs. 68, 71, oc), borne chiefly upon the hasioccipital, but to the formation of which the 
exoccipitals also contribute ; the latter flare widely on each side, into the tympanic wings, w^hich 
bound the external auditory meatus behind. The true hasioccipital is mostly covered by the 
underlying secondary bone, the hasitemporal (69, 70, ht), which extends from one tympanic 
cavity to the other, and more or less forward in the middle line to the sphenoidal rostrum. 
Openings to be observed in the occipital region, besides the great foramen, are those for the 
hypoglossal nerve, 9, near the condyle ; for the parts of the vagus nerve, 8, more laterally, and 
the carotid canal, ic: also, above the foramen magnum, openings for veins, sometimes of great 
size, as in fig. 63, j. 
The Parietals (figs. 62, and 70,^, 71). — Proceeding up over the brain-box, the next 
bones are a pair of parietals, between the occipital behind, the frontal before, and the squa- 
mosal beside ; but their limits are rarely if ever to be seen in adult skulls. They are relatively 
small in birds ; simply squarish plates, bounded as said, coming together in the midline. 
The Frontals (fig. 62, and 70,/, 71), originally paired, soon fuse together, and with sur- 
rounding bones of the skull, though maintaining some distinction fi-om those of the nose and jaw. 
These roof over much of the brain cavity, close in much of it in front, and form the roof and 
eaves of the great orbital sockets. Anteriorly in the middle of the forehead line the feet of the 
nasal process of the premaxillary are implanted upon the frontal, usually distinctly ; more 
laterally, the nasal bones are articulated or anchylosed ; this fronto-naso-premaxillary suture 
forming the fronto-facial hinge, (fig. 63, x) by the elasticity or articulation of which the upper 
jaw moves upon the skull, when acted on by the palatal and jugal bars. In the midst of the fore- 
head the two halves of the frontal sometimes separate, as they do in the fowl, allowing a little 
of the mesethmoid to come to the front. In the middle line, underneath, the frontals fuse with 
whatever extent there may be of the mesethmoid which forms the lengthwise inter-orbital 
septum, and often a crosswise partition between the orbital and nasal cavities. To the antero- 
external corners of the frontal are articulated or anchylosed the lacrymals. The post-frontal 
process,^ morphologically the post-frontal or sphenotic bone, bounds the rim of the orbit behind ; 
1 There is apparently some ambiguity in the use of the term " post-frontal " process by different authors. It 
woTild appear that this process, bounding the rim of tlie orbit beliind, may be a projection of the frontal bone, and 
therefore strictly a post-frontal process. Or that, as said by Owen for Bhea, it may be a separate bone, and there- 
