224 GENERAL ORNITHOLOGY part ii 



preliminary notion of the "lay of the land." I advise him to con- 

 template this picture till he has learned the names printed on it by 

 heart, and can apply them to the identification of the parts of the 

 real skull he should have in hand at the same time. He may also 

 meditate on Fig. 63. 



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 mtochord. Fig 64, c (Gr. vun-ov, noton, back; 

 Xop^> chords, a chord), 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. Trapd, 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 semicircular canals, hsc. Opposite the end of the notochord, 

 the border of the parachordal plate is notched, 5 ; this notch after- 

 ward forms the foramen ovale, for the passage of parts of the fifth or 

 trifacial nerve. Near the middle line, posteriorly, the plate is per- 

 forated for the passage of the twelfth or hypoglossal nerve, q. At 

 each lateral corner is the separate quadrate cartUage, 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 

 trabecules, tr (Lat. trabecula, a little beam), which enclose the pituitary 

 space, pts (Lat. pituita, mucus : no applicability here). In front of 

 this pituitary interval the trabeculse come together to form an inter- 

 nasal plate, which is so arched over downward as to disappear from 

 this view, as seen in Fig. 65, where fn is the frontonasal 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 only preoral arch). 



The same chick's head, now viewed from below. Fig. 65, shows 

 the squarish aperture, m, of the future mouth ; the three postoral 

 arches, vidth their respective cartilaginous bars, out of which are to 

 be formed the bones of the jaws and tongue. 1, 2, 3 are the cor- 

 responding 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 scaffolding of the upper and 

 under jaw. The curved suhocular or maxillopalatine bar, mxp, de- 

 veloped in the first postoral arch, already indicates anteriorly 

 palatine, pa, and posteriorly, pterygoid, pg, parts ; it will form the 



