150 



GENERAL ORNITHOLOGY. 



the back-bone be real and true, it is so obscured by the extraordiuay modifications to which 

 the vertebral elements have been subjected that the fact of such homology cannot be demon- 

 strated ; and to iuteqM'et the skull as something super-imposed upon, and morphologically 

 different from the spinal column, is pcrf<.'ctly "warranted if not required by the known facts of 

 its constructive development. This is the view taken by the rulers of to-day's science. As 

 already said (p. 137) the relation between cranial and vertebral parts is rather the anak)gy of 

 adaptive modification than a true homology of structure. 



Before proceeding to describe the mature skull, it \A-iIl bo best to consider its mode of 

 development. In this I shall closely follow Parker, often using the words of that master, and 

 illustrating the early stages of the embryo with figures lii^irrowed from the same safe source. 

 In the fewest words possible, I wish to convey an idea of the embryonic skull up to Parker's 

 'Hhird stage," at which it begins to ossify. Here, however, I will first insert a figure, kindly 

 draM-n for me by Dr. R. W. Shufeldt, of the U. S. Army, which shows most of the cranial 

 bones, and will give the student a preliminary notion of the "lay of the land." I advise him 

 to contemplate 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. 



Or. 



Sp^i*! 



Fig. 62. Skull of common fowl, enlarged; from nature by Dr. E. W. Shufeldt, U. S. A. The names of hones 

 and some other parts are printed, requiring no explanation; but observe the following points: The distinction of 

 none of the bones composing the brain-case (the upper back expanded part) can he found in a mature skull. The 

 brain is contained between the occipital^ i^phenoidals, squamosals ^ parietal s and part oi frontal ; the ethmoidals 

 belong to the same group of cranial bones proper. All other bones, excepting the three nf'w ear-bones, are bones 

 of the face and jaws. The lower jaw, of five bones, is drawn detached ; it articulates by the black surface marked 

 articular with the prominence just above — the quadrate hone. Observe that from this quadrate a series of bones 

 — quadrato-jugal, juf/al, maxillary — makes a slender rod running to the prem-axillary ; this is the zygoma, or 

 juf/al bar. Observe from the quadrate also another series, composed of pterygoid and palatine hones, to the pre- 

 maxillary ; this is the ptery go-palatine bar : it slides along a median fixed axis of the skull, the rostrum, which 

 bears the loose vomer at its end. The under mandible, quadrate, pterygoid, and vomer are the only movable bones 

 of this skull. But when the quadrate rocks back and forth, as it does by its upper joint, its lower end pulls and 

 pushes upon the upper mandible, by means of the jugal and pterygo-palatine bars, setting the whole scaffoldiiio' of 

 the upper jaw in motion. This motion hinges upon the elasticity of the bones of the foreliead, at the thin x>lace just 

 wliere the reference-lines from the words " lacrymal " and " mesethmoid " cross each other. The dark oval space 

 behind the quadrate is the external orifice of the ear; the parts in it to which the three reference-lines go are 

 diagrammatic, not actual representations ; thus, the quadrate articulates with a large pj^o-otic as well as with 

 the squamo.^aL The great excavation at the middle of the figure, containing the circlet of unshaded bones, is the 

 left or6i^a^ cavity, o?'?>i/, or socket of the eye. The mesethmoid includes most of the background of this cavity shaded 

 diagonally. The upper one of the two processes of bone extending into it from behind is the post-frontal or spke- 

 notic process ; the under one (j ust over the quadratel is the squamosal process. A bone not shown, the presphenoid, 

 lies just in front of the oval black space over the end of basisphen-oid. This black oval is the optic foramen^ 



