SFX. IV ANATOMY OF BIRDS 231 



the hasiteiivporal (Figs. G9, 70, bt), 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, jJ, 71). — Proceeding up over 

 the brain-box, the next bones are a pair of parietals between the 

 occipital behind, the frontal before, and the squamosal 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 upper mid-line, or sagittal suture. 



The Frontals (Figs. 62 and 70,/, 71), originally paired, soon fuse 

 together, and with surrounding bones of the skull, though main- 

 taining some distinction from 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 

 premaxillary are implanted upon the frontal, usually distinctly ; 

 more laterally, the nasal bones are articulated or ankylosed ; this 

 fronto-naso-premaxillary suture forming the frontofacial 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 forehead the two halves of the frontal some- 

 times 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 Avhatever extent there may be of the meseth- 

 moid which forms the lengthwise interorbital septum, and often a 

 crosswise partition between the orbital and nasal cavities. To the 

 antero-external corners of the frontal are articulated or ankylosed 

 the lacrymals. The posffrontal process,'^ morphologically the post- 

 frontal or sphenotic bone, bounds the rim of the orbit behind ; it 

 is usually quite prominent. The frontal rim of the orbit in many 

 birds shows a crescentic depression (very strong in a loon and many 

 other water-birds ; Fig. 63, w), for lodgment of the supraorbital 

 gland, the secretion of which lubricates the nasal passages. The 

 cerebral plate of the frontal is often imperfectly ossified, showing 

 large fenestra? besides the regular openings for the exit of nerves 



^ There is apparently some ambiguity in the iise of the term " postfroutal " 

 process by different authors. It would appear that this process, bounding the rim 

 of the orbit behind, may be a projection of the frontal bone, and therefore strictly a 

 postfrontal process. Or that, as said by Owen for Rhea, it may be a separate bone, 

 and therefore properly a iwstfrontal hone. Or, again, that it may have nothing to 

 do with the frontal bone, but belong to the alispheuoid, as a process of the latter or 

 a separate ossification ; in which case it would be properly the sj^henotic. In no 

 event has it anything to do with the squamosal process lettered as such in Fig. 62. ' 



