ANATOMY OF BIRDS 



229 



tion to those already noted. The ethmoidal wall ends behind at 

 J7X, the presphenoidal region, where the brain-case begins ; below 

 and behind, it is deeply notched for the oi^tic foramen, 2. The 

 pituitary space forms a circular foramen, through which the carotid 

 arteries enter. The site of the orbit of the eye is bounded behind 

 and below by the post-frontal process of the alisphenoid wing, fj of 

 as. The pterygopalatine rod is seen along the under border of the 

 skull, fg and 'pa. The quadrate, (/, has acquired nearly its shape, 

 and tlie rest of the mandibular and hyoidean parts are clearly dis- 



Fio. 69.— Skull of chick, third stage, 

 viewed from hdow, x 6| diameters, yn, 

 prenasal cartilage, running behind into tlie 

 septum nasi ; on eacli side of it tlie premax- 

 illary, jtx, of which the (inner) palatal and 

 (outer) dentary processes are seen (the upjier 

 nasal process hidden) ; inx, the maxillary, 

 developing inner process, the maxillopala- 

 tine, m.x'p ; pa, the palatal, well formed, 

 articulating behind with rhs, the sphenoidal 

 rostrum, its thickened under border, the 

 parasphenoid ; this will bear the vomer at 

 its end when that bone is developed ; j, 

 jugal, joining tox and 5j, the quadratojugal, 

 joining j and q, the quadrate ; mx to g, the 

 jugal bar or zygoma ; yg, the pterygoid, 

 making with pre the pterygopalatine bar, 

 joining q and pi- ; hi, the basitemporal, great 

 mat of bone from ear to ear, underflooring 

 tlie skull proper, as rhs, a similar formation, 

 does further forward ; ic, outer end fif 

 carotid canal, to run between the ht plate 

 and true floor of skull, and enter brain 

 cavity at original site of pituitary fossa 

 (Figs. 64, 66, ic) ; ty, tympanic cavity— ex- 

 ternal opening of ear ; as, alisphenoid, 

 bounding much of brain-box anteriorly, and 

 orbital cavity posteriorly ; psc, posterior 

 semicircular canal of ear, in opisthotic bone, 

 which will unite with the spreading eo, ex- 

 occipital, which will reach the condyle 

 shown in the middle line, above the foramen 

 magnum, fm, completed above by so, supra- 

 occipital ; 8, foramen lacerum posterius, 

 exit of pneuraogastric, glossopharyngeal 

 and spinal accessory nerve ; 9, exit of hypo- 

 glossal nerve, in basioccipital. (After 

 Parker.) 



played, Hi/j, etc. The proximal hyoidean element, st, is freed from 

 the periotic cartilage, leaving the fenestra ovalis (see last paragraph). 

 Below the general outline, pa to oc, is not shown a mat of soft 

 tissue, in which are to be developed the basitemporal and parasphen- 

 oid bones which underfloor the Avhole skull, — the former making a 

 plat between the ears. Fig. 69, ht, the latter forming the thickened 

 under edge of the rostrum of the skull rhs. 



At the third stage, about the middle of the second week of in- 

 cubation, the cartilaginous parts already described are neatly finished, 

 and the skull is beginning to ossify. The occipital parts are well 



