158 



GENERAL OBNITROLOGY. 



sloping with less distinction in front toward the orbital cavity. In this auditory hollow may be 

 eeen several openings : the meatus or proper ear-passage, through which, in one direction, a 



bristle may be passed to emerge at or near 

 the middle line of the base of the skull, 

 about the root of the basisphenoidal ros- 

 trum. Such a passage is through the first 

 visceral cleft of the early embryo, modi- 

 fled intQ meatus auditorius and eustachian 

 tube, which latter communicates with the 

 back part of the mouth. Besides the other 

 ear-passages proper, may be found otlier 

 openings of airrpassages leading into the 

 interior diploic tissue of bones of the 

 skuU, and especially into the lower jaw 

 bone. The ear-parts are immensely de- 

 veloped in owls, in many species of 

 which they are unsymmetrical, that is, 

 not sized and shaped alike on right and 

 left sides of the head. 



The Sphenoid (Gr. (T4>fiv, sphen, a, 

 wedge ; effios, eidos, form ; flgs. 62, 70, 

 71) is a compound bone, not easy to un- 

 derstand as it occurs in birds, as much 

 of it is hidden from the outside, some of 

 it is very shghtly developed, and all of it 

 is completely consolidated with surround- 

 ing bones in the adult. It is wedged 

 into the very midst of the cranial bones 

 proper, with its body in the middle line 



Fig. 70. — Ripe chick's skull, longitudinal section, viewed below, next in front of the basioccipital, 

 inside, x 3 diameters ; after Parker. In the mandible are seen : 

 mk, remains of meckelian rod ; d, dentary bone; sp, splenial ; 

 a, angular ; sii, surangular ; ar, articular ; iap, internal articu- 

 lar process; pap, posterior articular process. In the skull: pn, 

 the original prenasal cartilage, upon which is moulded the pre- 

 maxillary, px, with its nasal process, npx, and dentary process, 

 dpx ; 871, septo-nasal cartilage, in which is seen nn, nasal nerve ; 

 nth, nasal turbinal ; the reference line crosses the cranio-facial 

 sutwre, the face parts and cranial parts being nearly separated 

 here by the nick seen in the original cartilaginous plate; eth, 

 ethmoid ; pe, perpendicular plate of ethmoid, which will spread 

 nearly throughout the dotted cartilaginous tract in which it lies, 

 to form nearly all the interorbital septum ; transverse thicken- 

 ing {in some birds) below the reference line eth will form the 

 pre-ftqntal, or orbito-nasal septum ; iof, inter-orbital foramen ; 

 ps, pre-sphenoidal region, just above which Is the orbito-sphe- 

 noidal region ; 2, optic foramen ; as, alisphenoid, with 5, foramen 

 for divisions of the Bth ( trifacial) nerve ; /, frontal ; sq, squamosal ; 

 p, parietal ; so, superoccipital ; asc, anterior semicircular canal ; 

 $c, a sinus (venous canal); ej}, epiotlc; eo, exoccipltal; op, opis- 

 thotic : po, prootic, with 7, meatus auditorius internus, for en- 



and its wings spread on either side in the 

 orbital cavity. A sphenoid consists es- 

 sentially of the basisphenoid, or main 

 part of the bone (flg. 62); the alisphe- 

 noids or " wings," on either side (flgs. 70, 

 71 , as) ; the obscure presphenoid, {ps) in 

 the middle line in front of and above the 

 main body; and the small orbito-sphe- 

 noids, wliich are in fact the wings of the 

 presphenoid. The body is usually covered 

 in by the underfloqring of the basitem- 

 poral ; it is a flat triangular plate, pro- 

 duced more or less forward in the middle 

 line as the basisphenoidal rostrum, or 

 beak of the skull. This rostrum is an 

 It forms, in fact, the 



trance of 7th nerve ; 8, foramen for vagus nerve; &o, basioccipi- 

 tal ; bt, basitemporal ; ic, canal (in original pituitary space ; important thins, 

 flg. 66 ie) by which carotid artery enters brain cavity ; asp, basi- ^ . /■ i i 

 pterygoid process; ap to rbs. rostrum of the skull, being the central asas of the base of the skull ; 

 parasphennid bone unrlerflooring the basisphenoid and future ,^-^^1^ ^jjg mesethmoid plate the inferior 

 perpendicular plate of ethmoid. (The scaffolding of the upper j. i . ■, • ■, 

 jaw not shown, excepting pa:, &c.) border 01 the interorbital septum, usually 



