TEE BONES IN BIRDS. 161 



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 gi'oove. 

 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 (Fig. 110, 1), incomplete, is supported by a particular piece 

 (posterior frontal) fixed between the principal frontal bone, parietal, and posterior 

 sphenoid, with which it is sometimes confounded. The perpendicular lamina of 

 the ethmoid is considerable, and forms between the two orbits a thin vertical 

 septum (Fig. 109, 8). Its posterior border is notched opposite to the optic 

 foramen, and thus constitutes an opening which communicates between the two 

 orbital cavities (Fig. 109, 9). It is also channeled, near its upper. border, by 

 a fissm-e which terminates by two openings at its extremities, one entering the 

 cranium, the other the nasal cavities. Tliis fissure and these foramina pennit 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, and forms part of the anterior orbital wall. These 

 cells replace, at the same time, the lateral masses of the ethmoid and turbinated 

 bones of MammaUa. The sphenoid appeal's 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 interoi-bital 

 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.^ The temporal bones present at their base an articular surface correspond- 

 ing to the square bone (os qimdratum) (Fig. 109, 12, 12'). In the Foivl 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 consolidated 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 prolonga- 

 tion of the OS unguis, forming with it a real bony arch. This arch limits, below 

 and outwardly, the orbital cavity. 



Bones of the face. — The supermaxilla comprises : a premaxilla, two nasal, two 

 lachrymal, two palatine, two pterygoid, two zygomatic hones, and a vomer. The 

 inferior jaw has for its base a maxillary hone, which articulates with the cranium 

 by means of two supplementary pieces named the square hones. The premaxillary 

 hone (Fig. 110, 10) is formed, before hatching is completed, of two lateral pieces, 



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

 ietermiuation of the interorbital septum. We are tempted, indeed, to consider this bony 

 lamina as the inferior sphenoid and the middle portion of the ethmoid in Birds. This manner 

 of viewing it tends to confirm the ideas of M. Tabourin on the inferior sphenoid and the 

 ethmoid of Mammals. 



