THE ANATOMY OF BIRDS. — OSTEOLOGY. 
151 
through which the nerve of sight passes from the brain-cavity to the eye. Tlie black clot a little behind the optic 
foramen is the oritice of exit of a part of the trifacial nerve. The black mark under the letters " on " of the word 
'* frontal" is the olfactory foramen, where the nerve of smell emerges from the brain-box to go to the nose. The 
nasal cavity is the blank space behind 7iasal and covered by that bone, and in the oval blank before it. The parts 
of the beak covered by horn are only premaxillary, nasal, and dentary. The condyle articulates with the first 
cervical vertebra ; just above it, not shown, is the foramen magnum, or great hole through which the spinal medulla, 
or main nervous cord, passes from the skull into the spinal column. The hasioccipital is hidden, excepting its 
condyle; so is much of the basisphenoid. The prolongation forward of the basisphenoid, marked " rostrum," and 
bearing the vomer at its end, is the parasphenoid, as far as its thickened under border is concerned. Between the 
fore end of the pterygoid and the basisphenoidal rostrum, is the site of the basipterygoid process, by which the 
bones concerned articulate by smooth facets; further forward, the palatines ride freely upon the parasphenoidal 
rostrum. In any Passerine bird, the vomer would be thick in front, and forked behind, riding like the palatine 
upon the rostrum. The palatine seems to run into the maxillary in this view ; but it continues on to premaxillary. 
The maxillo-palatine is an important bone which cannot be seen in the figure because it extends horizontally into 
the paper from the maxillary about where the reference line " maxillary " goes to that bone. The general line 
from the condyle to the end of the vomer is the cranial axis, basis cranii, or base of the cranium. This skull is 
widest across the post-frontal; next most so across the bulge of the jugal bar. 
Fig. 63. — Skull of a duck ( Clangula islandica), nat. size ; Dr. R. W. Shufeldt, U. S. A. a, premaxillary bone ; 
b, partly ossified internasal septum; b^, pervious part of nostril ; c, end of premaxillary, perforated for numerous 
branches of second division of the fifth cranial nerve ; d, dentary bone of under mandible ; e, groove for nerves, etc. ; 
/, a vacuity between dentary and other pieces of the mandible ; g, articular surface ; h, recurved " angle of the jaw ; " 
i, occipital protuberance; vacuity in supraoccipital bone; Ic, muscular impression on back of skull; I is over the 
black ear-cavity; m, post-frontal process; n, quadrate bone; o, pterygoid; 2^> palatine; q, quadrato-jugal ; r, 
jugal; s, maxillary ; t, fronto-parietal dome of the brain-cavity; ti, the lacrymal bone, immense in a duck, nearly 
completing rim of the orbit by approaching m; v, vomer; tv, supra-orbital depression for the nasal gland 
(see p. 157); x, cranio-facial hinge; y, optic foramen; z, etc., interorbital vacuities. 
Development of the Fowl's Skull (figs. 64 to 69). — In the chick's head cartilage is 
formed along the floor of the skull by the fifth day of incubation. This cartilaginous basilar 
plate is formed on each side of the notochord, fig 64, c (Gr. varov, noton, back ; x^P^j cliorde^ a 
€hord), a rod -like structure, the primordial axis of the body, around which, along the spinal 
column, the bodies of the vertebrae are formed, and which runs in the middle line of the floor 
of the skull as far as the pituitary space, pts. The basilar plate is the parachordal (Gr. rrapd, 
para, by the side of) cartilage. In this, at the earliest stage, are already planted certain parts 
of the ear, the cochlea, cl, (Lat. cochlea, a snail-shell), and the horizontal one of the three semi- 
circular canals, hsc. Opposite the end of the notochord, the border of the parachordal plate 
is notched, 5 ; this notch afterward forms the foramen ovale, for the passage of parts of the 
fifth or trifacial nerve. Near the middle line, posteriorly, the plate is perforated for the 
passage of the twelfth or hypoglossal nerve, q. At each lateral corner is the separate quadrate 
cartilage, to form the quadrate bone. Anteriorly, the plate connects by a strap or bridge 
of cartilage, the lingula, Ig (Lat. lingula, a little tongue) with the trabeculce, tr (Lat. trabe- 
cula, a little beam) , which enclose the pituitary space, pts (Lat. pituita, mucus : no applica- 
bility here). In front of this pituitary interval the trabeculae come together to form an inter- 
