8 ELEMENTARY SKETCH OF THE OSTEOLOGY OF BIRDS. 



The upper part of the brain-case (pi. II., %. 2, fr. to pa.) con- 

 sists in the adult bird of a smooth spherical surface of bone 

 without any distinct sutures. The median line of the skull, 

 however, shows a depressed channel, which indicates the ori- 

 ginal line of union between the large bones which form this part 

 of the skull, and which are termed ihoi frontals (fr. )* The frontals 

 in the adult appear to extend backwards as far as the supra- 

 occipital, but in reality a pair of bones (pa.) are interposed, 

 which correspond to the parietalsf of man. These bones in 

 the adult are indistinguishably anchylosed together in the 

 median line, and in front and behind to the frontals and supra- 

 occipital. The portion of the skull which forms the division 

 between the two orbits (o. pi. I) consists of a very thin verti- 

 cal septumi which may be completely ossified, or which may 

 present one or more vacuities which are occupied by membrane in 

 the living animal. This septum chiefly consists of bones which 

 correspond to the ethmoid§ and the pre- and orbito-sphenoidsjl 

 of mammals. A part of the ethmoid also appears on the top 

 of the skull, between the anterior extremities of the frontals 

 (eth. fig., 2 ; pi. II.) In part of this ethmoidal septum, in the 

 dry skull, there is usually a vacant space, and then we come 

 to another anteriorly placed thin vertical septum, separat- 

 ing the two nasal cavities. This latter septum is often very 

 incompletely ossified. Within the nasal cavities are contained 

 the tiirbinal'^ bones which carry the mucous membrane of 

 the nose. Inferiorly the bird-skull (pi. II., figs. 1, 3, 4, 5) 

 comprizes, in addition to the bones which we have already 

 noticed, the 'pterygoids (pt.)** which articulate posteriorly 

 with the quadrate bones fqu.) and anteriorly with either the 

 vomer (vo.)tt or the "palatines (pi.) The palatines them- 

 selves (pi.) are moveably united either partly together and 

 partly with the sphenoidal rostrum (sph. r.) or with the vomer. 

 The latter (vo.) is a mesial bone of various forms occupying the 

 anterior part of the lower surface of the skull. This bone is 



* Frontal, from frons, the forehead; the bones situated immediately above the 

 orbits. 



t Parietal, from 'paries, a wall; the bones roofingf the brain-case behind the 

 frontals. 



J Septum, properly an enclosure, and then a partition. 



§ Ethmoid, from ^dfxo? a sieve ; the bone forming the septum of the nose ; so 

 named from its spongy and perforated nature in man. 



II Pre- and orbito-sphenoids. See note on sphenoidal rostrum given above. 



% Turbinal, from turbo a top, applied to the bones of the nasal cavities, from their 

 twisted character. 



** Pterygoids (from TtTepvt, a wing, and ttoof likeness) are small bones articulat- 

 ing with and placed behiad the palatines in mammals ; in human anatomy called 

 pterygoid processes of the sphenoid. 



f f Vomer, a ploughshare ; applied to a median bone at the forepart of the lower 

 surface of the skull. 



