150 



GENEBAL ORNITHOLOGY. 



the baek«^l)OTie 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 

 difierent 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 will be best to consider its mode of 

 development. In this 1 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 

 "third 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. 



riG. 62. — Skull of common fowl, enlarged ; from nature ty Dr. E. W. Shufeldt, tJ. S. A. The names of bones 

 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 be found in a mature skull. The 

 brain is contained between the occipital, sphenmdals, sqvmnosals, parietals and part of frontal ; the etlvmoiddla 

 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 bone. Observe that from this quadrate a series of bones 

 — guadrato-jugal, jugal, maxillary — makes a slender rod running to the pr&maxilla^ ; this is the zygoma, or 

 jugal bar. Observe from the quadrate also another series, composed of pterygoid and palatine bones, to the pre- 

 maxiUary ; 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 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 bther.^ 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 bones, is the 

 left orbital ca/vity, 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- 

 nctic process ; the under one {just overthe quadrate) is the squanwsalprocess. 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. 



