152 GENERAL ORNITHOLOGY. 
nasal plate, which is so arched over downward as to disappear from this view, ns seen in 
fig. 65, where fn is the fronto-nasal process, and # is tho future oxternal nostril, Atter 
uniting in the inter-nasal plate, the fore ends of the trabecula separate and becomo free 5 their 
free ends are the under extremities of this jirst visceral arch (first and only pre-oral arch). 
The same chick’s head, now viewed trom below, fig. 65, shows the squarish aperture, m, 
of the future mouth ; the three post-oral arches, with their respective cartilaginous bars, out, 
of which are to bo formed tho bones of the jaws aud tongue. 1, 2, 8, are tho corresponding 
visceral clefts, betweon the arches; the first of theso is to be modelled into the ecar- 
passages (outer and middle ear and eustachian tube) ; the others will disappear. The quadrate 
cartilage, q, is the same that was seen in fig. 64; it is already nearly in position, between the 
hind ends of the scaffolding of the upper and under jaw. The curved subocular or inaillo- 
palatine bar, map, developed in the first post-oral arch, already indicates anteriorly palatine, 
pa, and posteriorly, pterygoid, pg, parts; it will form tho bones so named, and others of the 
Fria, 65.—Samo os fig. 64, but scon from below, 
cvl, anterior corebral vesicle; «, eye; m, mouth; pis, 
pituitary space; 7, fronto-nasal plato; fr, ouds of the 
Fia. 64.— Skull of chick, fifth day of incubation, 
9 diameters. Seen from above, the membranous roof 
of the skull and the brain removed, cv1, anterior cere- 
bral vesicle ; ¢, eye; c, notochord, running through the 
middle of the basilar plate or parachordal cartilage, in 
which are already visible the rudimentary ear-parts, ¢/, 
the cochlea, hse, the horizontal semicircular canal ; pts, 
the pituitary space, bounded by ¢r, the trabeculm, 
which come together before {t to form the fronto-nasal 
plate, fn, in fig. 65; lg, lingula or bridge connecting 
trabeculae with parachordal cartilage ; 5, notch after- 
ward becoming foramen ovalo for passage of parts of 
the fifth (trifacial) nerve ; 9, foramen for hypoglossal 
nerve; g, separate cartilage forming the future quad- 
rate bone. (After Parkor, in Zncy. Brit.) 
trabeculs, freo again aftor their union wd bent strong- 
ly from the original axis of the trabeculae; nm, oxter- 
nal nostril; my, subocular bar of cartilage, or ptery- 
go-palatine rod, to form pa, palatine, and pg, ptorygold 
bone, and other parts of the uppor jaw, ax the maxil- 
lary, Jugal and quadrato-jugal; q, quadrate cartilage, 
same as soon in fig. 64; mA, meckolian cartilage, to form: 
lower jaw; those prrix are In the first post-oral visceral 
arch; ch, corato-hyal, and 6h, basthyal, of second post- 
oral arch; ebr, corato-branchial, cbr, epi-branchtal,. 
bbr, basi-branchial, of third post-oral arch; the »arts 
of the second and third arch all going into the yold 
bone. 1, 2, 38, tl, 2d, 8d vinceral clefts, whoreof une Let 
is to be modified into the car-passages, and the others 
are to be obliterated, (After Parker.) 
upper jaw. This suboeular bar is an antero-suporior part. of the first post-oral arch, of which 
q and mk are a postero-inferior portion; the cleft of the future mouth is to lie between them. 
The lower jaw bone, or mandible, is entirely developed from mk, its several bones developing 
around this rod of cartilage, the meckelian cartilage ; it is to become movably articulated with 
the bone, the quadrate, into which q will be transformed. Thus the postero-inforior part of 
the first post-oral arch (second of the whole series of arches) hegins in two pieces, one of which 
is to become the suspensorium, or suspender of the mandible, and the other the mandible 
