THE ANATOMY OF BIRDS. — OSTEOLOGY. 



167 



insertion of the temporal or masseteric muscles which effect closure of the jaw. It is scarcely 

 evident in the fowl, fig. 63, hut well marked in the duck, fig. G.j, over/. At the hack of tlie 

 articular surface is the pneumatic foramen for entrance of air, when any ; on the inner surface 

 of the ramus, ahout the spleuial hone, is the opening conveying the vessels and nerve. 



The Hyoitl Bone (Gr. letter v, /we^liy, fiSos, eidos, form; figs. 

 05-68, 72-74j is the skeleton of the tongue; a very composite struc- 

 ture, consisting of several distinct hones, developed in the second and 

 third post-oral visceral arches (see fig. 65, where ch and hh are the 

 original elements of the second arch, making tlie hasilnjal and cerato- 

 hyal hones, and hhr, cbr, and ebr are the original elements of tlie third 

 arch, making the basibranchial, cerato-branchial, and epihranchial 

 b(jnes). The whole affair is somewhat ^- or fj^-shaped, lying 

 loosely, point forward, between the forks of the lower jaw, with its 

 long slender prongs curving up behind the hind head more or less; 

 but not definitely connected with any other bones of the skull. The 

 connection which e.xists between tlie hyoid and other cranial bones 

 in a mammal is in birds broken by non-development of certain 

 linlis of hone developed in the mammalian second post-oral arch, as 

 the stylo -hyal, epihyal, etc. ; thougli birds have a rudimentary stylo- 

 hyal, at least in the embryo, among the several proximal parts of 

 the second arch which form the intricate bones within the ear- 

 passages (fig. 67). The visible parts of a bird's hyoid are usually: 

 the body of the bone, basihyal (bh, and fig. 72, c), single and median, 

 commonly quite sliort and stocky, sometimes long and slender. The 

 basihyal bears in front ii pair of cerato-hyals (ch; not shown in 

 .fig. 73, where they have been absorbed in 6) usually movably 

 articulated with the basihyal. They commonly appear as little 

 " horns " or processes of the next piece, the glo-iso-hyal (fig. 72, b) 

 cjr bone chiefly supporting the substance of the tongue. It may be 

 a stout and apparently single bone, as that of the goose figured ; but 

 oftener appears as a pair of slender bones, side by side, whoso back- 

 ward ends are the cerato-hyals. The glossohyal may or may not 

 hear at its fore end a cartilaginous tip, as in fig. 72, a. All the foi-e- 

 going are hyal, i. e., belonging to the second visceral arch; the 

 following are branchial, of the third arch : The basi-branchial 

 (bbr, fig. 72, d) is a single median piece, projecting backward 



Fig. 72. — Hyoid bones of a 



from the basihyal, with which it may be perfectly consolidated, as goose, nat. size; by Dr E. w. 

 it is in the figure, or separately articulated ; it may be wanting ; it 

 is usually tipped and prolonged hackward with a thread of cartilage. 

 The basibranchial is oftener called " urohyal," but had better be 

 allowed its strict morphological name. On either side, the basihyal 

 bears the separately articulated cerato-brunchiah (cbr, fig. 72, e), 

 long slender bones diverging as they pass backward, and bearing 

 upon their ends the epi-branchials (ebr, fig. 72,/), whiclr finish off 

 the hyoid bone behind, or may be in turn tipped with cartilaginous 

 threads. The cerate- and epi-branchials togetlier are liadly called IJ-ya-ls," or " greater 

 the " thyro-hyals," and in still more popular language the "greater cornua" or "horns" 

 of the hyoid. All these hones vary in different birds in size and shape and relative develop- 

 ment ; the branchial elements are the most constant in their length and slenderness. The 



Sliufelilt, U. S. A. a, ear- 

 tilaginous end-piece of b, the 

 great giosso-liyal, wliieli lias 

 absorhe<l or replaced cerato- 

 liy.'ils or "lesser oornua"; c, 

 basiliyal, movably articulated 

 with b, :tnd conibhied com- 

 Iiletely with fK basitiranchial, 

 commonly called " urohyal; " 

 e, ceratobrancliial; /, epi- 

 brancliial ; e and / are to- 

 gether known as "thyro- 

 cornua." 



