152 
GENERAL OBNITHOLOGY. 
nasal plate, which is so arched over downward as to disappear from this view, as seen in 
fig. 65, where fn is the fronto-nasal process, and n is the future external nostril. After 
uniting in the inter-nasal plate, the fore ends of the trabeculse separate and become free ; their 
free ends are the under extremities of this first visceral arch (first and onlypre-oral arch). 
The same chick's head, now viewed from 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 be formed the bones of the jaws and tongue. 1, 2, 3, are the corresponding 
visceral clefts , between the arches ; the first of these is to be modelled into the ear- 
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 scafiblding of the upper and under jaw. The curved suhocular or maxillo- 
palatine bar, mxp, developed in the first post-oral arch, already indicates anteriorly palatine, 
pa, and posteriorly, pterygoid, pg^ parts ; it will form the bones so named, and others of the 
Fig. 64. — Skull of chick, fifth day of incubation, 
X9 diameters. Seen from above, the membranous roof 
of the skull and the brain removed, cvl, anterior cere- 
bral vesicle ; e, eye ; c, notochord, running through the 
middle of the basilar plate or parachordal cartilage, in 
which are already visible th6 rudimentary ear-parts, cl, 
the cochlea, lisc, the horizontal semicircular canal ; pts, 
the pituitary space, bounded by tr, the trabeculse, 
which come together before it to form the fronto-nasal 
plate, fn, in fig. 65; Jg, lingula or bridge connecting 
trabeculae with parachordal cartilage ; 5, notch after- 
ward becoming foramen ovale for passage of parts of 
the fifth (trifacial) nerve ; 9, foramen for hypoglossal 
nerve ; q, separate cartilage forming the future quad- 
rate bone. (After Parker, in Ency. Brit.) 
Fig. 65. — Same as fig. 64, but seen from below, 
crl, anterior cerebral vesicle; c, eye; ?n, mouth ; 
pituitary space ; fn, fronto-nasal plate ; tr, ends of the 
trabeculie, free again after their union and bent strong- 
ly from the original axis of the trabeculie; n, exter- 
nal nostril ; mxp, subocular bar of cartilage, or ptery- 
go-palatine rod, to form ya, palatine, and i)g, pterygoid 
bone, and other parts of the upper jaw, as the maxil- 
lary, jugal and quadrato-jugal; q, quadrate cartilage, 
same as seen in fig. 64; mk, meckelian cartilage, to form 
lower jaw ; these parts are in the first post-oral visceral 
arch; ch, cerato-hyal, and hli, basihyal, of second post- 
oral arch; chr, cerato-branchial, e&r, epi-branchial, 
hhr. basi-branchial, of third post-oral arch ; the parts 
of the second and third arch all going into the hyoid 
bone. 1, 2, 3, 1st, 2d, 3d visceral clefts, whereof the 1st 
is to be modified into the ear-passages, and the others 
are to be obliterated. (After Parker.) 
upper jaw. This subocular bar is an antero- superior 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 mJc, its several bones developing 
around this rod of cartilage, the mecTcelian cartilage ; it is to become movably articulated with 
the bone, the quadrate, into which q will be transformed. Thus the postero-inferior part of 
the first post-oral arch (second of the whole series of arches) begins in two pieces, one of which 
is to become the suspensorium, or suspender of the mandible, and the other the mandible 
