THE BONES IN BIRDS. 115 



Bones of the cranium. The bones which compose the cranium are, as in mammalia, 

 an occipital, parietal, frontal, ethmoid, sphenoid, and two temporals. These bones are 

 net isolated from each other, excepting during early life in the shell; and the ossifying 

 process which unites them is so rapid, that the cranium, shortly after hatching, is 

 already a single piece. No detailed description of the separate bones will be given here, 

 but only a few brief observations which may be of some utility. 



Thus, the occipital bone shows for articulation with the spine only a single condyle, 

 situated under the occipital foramen, and excavated by a slight groove. In palmipedes, 

 this bone is pierced, behind the crests which give attachment to the extensor muscles, 

 by two foramina which penetrate the cranium, and represent permanent fontanella. 

 The parietal bone is feebly developed, and formed from only two primary nuclei. 

 The frontal is the largest bone of the cranium; its orbital process is supported 

 by a particular piece which is generally considered as belonging to the large wing 

 of the sphenoid. The perpendicular lamina of the ethmoid is considerable, and 

 forms between the two orbits a thin vertical septum (fig, 73, 8). Its posterior border is 

 notched opposite to the optic foramen, and thus constitutes an opening which com- 

 municates between the two orbital cavities (fig. 73, 9). It is also channeled, near its 

 upper border, by a fissure which terminates by two openings at its extremities, one 

 entering the cranium, the other the nasal cavities. This fissure and these foramina 

 permit the passage of the ethmoidal nerve, which in this way traverses the orbit before 

 arriving at its destination. The ethmoidal cells are more membranous than bony ; their 

 base is attached to a very delicate transverse plate, which is often membranous and not 

 cribbled, a; id forms part of the anterior orbital wall. These cells replace, at the same 

 time, the lateral masses of the ethmoid and turbinated bones of mammalia. The 

 sphenoid appears to be formed of a single piece, and shows on its sides two diarthrodial 

 facets corresponding to the pterygoids. It is pierced by one foramen for the passage of 

 the optic nerves ; but this foramen opens on the outer and opposite side of the posterior 

 notch of the interorbital septum, and thus allows each of the nerves passing through it 

 to reach the eye for which it was intended. 



It is worthy of remark, that an analogous disposition is also noticed in the rabbit. 1 

 The temporal bones present at their base an articular surface corresponding to the square 

 bone. In the fowl species, the zygomatic process forms a small flattened tongue, 

 directed forwards, sometimes free, and at other times united by its superior border 

 to the summit of the orbital process. These two eminences are exceedingly short 

 in pigeons. In palmipedes they are consolidate;! and confounded so intimately, that it 

 becomes impossible to distinguish them from one another. From this union results a 

 long and strong process, which inclines forward and meets a particular prolongation of 

 the os unguis, forming with it areal bony arch. This arch limits, below and outwardly, 

 the orbital cavity. 



Bones of the face. The supermaxilla c mprises : a premaxilla, two nasal, two 

 lachrymal, two palate, two pterygoid, two zygomatic bones, and a vomer. The inferior 

 jaw has for its base a maxillary bone, which articulates with the cranium by means of 

 two supplementary pieces named the square bones. The premaxiliary bone is found, 

 before hatching is completed, of two lateral pieces, which represent the two small 

 premaxiilanes of mammals. This bone is very considerable, and of itself forms the base 

 of the upper beak, whoso form it determines ; it is pointed and conical in the gaUinacea, 

 and wide and flattened above and below in palmipedes. In front it circumscribes the 

 external openings of the nose, and is prolonged superiorly into two lengthy processes 

 which dovetail between the nasal bones. Two inferior processes belonging also to this 

 bone concur in the formation of the palatine roof. The supermaxillaries, analogues of 

 the fcupermaxillaiies of mammals, are two rudimentary bones situated on the sides and 

 at the base of the beak. They form a part of the palatine roof and the walls of the 

 nasal cavities. The nasal bones circumscribe above, inwardly, and even outwardly, the 

 external orifices of these cavities. The palate bones encircle, as in mammals, the guttural 

 openings of the nose, and constitute in great part the roof of the palate ; their posterior 

 extremity lies against the pterygoids ; the anterior joins the snpermaxillaries and the 

 inferior process of the premaxiliary bone. The pterygoids extend obliquely from the 

 sphenoid to the square bones, and are united to the sphenoid by diarthrodial articulation. 



1 This analogy is really striking, and might, in our opinion, serve as a basis for 

 a new determination of the interorbital septum. We are tempted, indeed, to consider 

 this bony lamina as the inferior sphenoid and the middle portion of the ethmoid of birds. 

 This manner of viewing it tends to confirm the ideas of M. Tabouriu on the inferior 

 sphenoid and the ethmoid of mammals. 



