THE ANATOMY OF BIRDS. — OSTEOLOGY. 



167 



through wliich the nerve of sight passes from the brain-cavity to the eye. The black dot 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 nasal and covered by that bone, and in the oval blank before it. The parts 

 of the beak covered by horn are only premaxiUnry, 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 basioccipital 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 lar 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 tigure 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. — f>ku\\ of a, duclii riangitlaislandica\nat. size; Dr. R. W. Shufeldt, U S. A. a. premaxillary bone; 

 b. partly ossifled 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; k, muscular impression on back of skull; / is over the 

 black ear-cavity; jn, post-frontal process; n, quadrate bone; o, pterygoid; p, palatine; q, quadrato-jugal; r, 

 jugal; s, maxillary ; t, fronto-parietal dome of the brain-cavity; u, the lacrymal bone, immense in a duck, nearly 

 completing rim of the orbit by approaching m; v, vomer: u\ supra-orbital depression for the nasal gland 

 (see p. 1C3); x, cranio-facial hinge; y, optic foramen; z, etc., interorbital vacuities. 



Development of the Fowl's Skull (figs. 64 to G9). — 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 th notochord, fig 64, c (Gr. vwtov, noton, back ; x°P^' chorde, a 

 chord), a rod-like structure, the primordial axis of the body, around which, along the spinal 

 column, the bodies of the vertebrae are fi)rmed, 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. jrapa, 

 para, by the side of) cartilage. In this, at the earliest stage, are already ])lanted certain ])arts 

 of the ear, the cochlea, cl, (Lat. cochlea, a snail-shell), and the horizontal one of the tliree semi- 

 circular canah, 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 ])erforate(l for the 

 jKissage of the twelfth or hj/jwrjlossal 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 lingtda, Ig (Lat. lingula, a little tongue) with the trahecidfc, tr (Lat. trabe- 

 cida, a little b<'ani), which enclose the pituitary sjmce, pts (Lat. pituita, mucus: no a]>pliea- 

 bilitv hen). Ill front of this pituitary interval the trabeculae come together to form an inter- 



