150 
GENERAL OBNITHOLOGY. 
the back-bone be real and true, it is so obscured by the extraordinay modifications to which 
the vertebral elements have been subjected that the fact of such homology cannot be demon- 
strated ; and to interpret the skuU as something super-imposed upon, and morphologically 
different from the spinal column, is perfectly 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 analogy of 
adaptive modification than a true homology of structure. 
Before proceeding to describe the mature skull, it wiU be 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 borrowed 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 
drawn 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. 
Fig. 62. — Skull of common fowl, enlarged; from nature by Dr. R. W. Shufeldt, U. S. A. The names of bones 
and some other parts are printed, requiring no explanation; Ibut observe the following points: The distinction of 
none of the bones composing the brain-case (the upper back expanded part) can be found in a mature skull. The 
brain is contained between the occipital, sphenoidals, squamosals, parietcUs and part of. frontal ; the ethmoidals 
belong to the same group of cranial bones proper. All other bones, excepting the three otic 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, jugal, maxillary — makes a slender rod running to the premaxillary ; this is the zygoma, or 
jugal bar. Observe from the quadrate also another series, composed of pterygoid and palatine bones, to the pre- 
maxillary ; this is the pterygo-jjalatine bar ; it slides along a median fixed axis of the skull, the rostimm, 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 scaffolding of 
the upper jaw in motion. This motion hinges upon the elasticity of the bones of the forehead, at the thin place just 
where 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 pro-otic as well as with 
the squamosal. The great excavation at the middle of the figure, containing the circlet of unshaded bone.s, is the 
left orbital cavity, orbit, 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 sphe- 
notic process ; the under one (just over the quadrate) is the squamosal process. A bone not shown, the presphenoid, 
lies just in front of the oval black space over the end of basisphenoid. This black oval is the optic foramen, 
