THE ANATOMY OF BIRDS. — OSTEOLOGY. 



167 



iusortion of the temporal or masseteric muscles which eflFect closure of the jaw. It is scarcely 

 evident in the fowl, fig. 62, but well marked in the duck, fig. 0:^, over/. At the hack of the 

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

 of tlie ramus, about the spleuial bone, is the opening conveying the vessels and nerve. 



The Hyoid Bone (Gr. letter i, /u«:=hy, elbos, eidos, form; figs. 

 (io-OS, 72-7i) is the skeleton of the tongue; a very composite struc- 

 ture, consisting of several distinct bones, 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 the basihyal and cerato- 

 hi/al bones, and bbr, cbr, and ebr are the original elements of the third 

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

 bones). The whole affair is somewhat A" or n.-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 exists between the hyoid and other cranial bones 

 in a mammal is in birds broken by nou-devek)pmeut of certain 

 links of bone developed in the mammalian second post-oral arch, as 

 the stylo -hyal, epihyal, etc. ; though 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, 

 (Mmmonly quite short and stocky, sometimes long and slender. The 

 bas^iliyal bears in front a pair of cerato-hyals {ch; not shown in 

 tii:. 72, where they have been absorbed in b) usually movably 

 articulated with the basihyal. They commonly appear as little 

 " horns " or processes of the next piece, the glossp-hyal (fig. 72, 6) 

 or 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, whose back- 

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

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

 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 

 from the basihyal, with which it may be perfectly consolidated, as 

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

 is usually tipped and prolonged backward 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-branchials (ebr, fig. 72, e), ^^^^^^^ ^.^^ ^^ basibranchial, 

 long slender bones diverging as they pass backward, and bearing commonly called "urohyal;" 

 upon their ends the epi-branchials {ebr, fig. 72, /j, which finish off ^VancSrrtnd^/ ieTo- 

 the hyoid bone behind, or maybe in turn tipped with cartilaginous gether known as "thyro- 

 threads. The cerato- and epi-branchials together are badly called i^yais," or " greater comua." 

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

 of the hyoid. All these bones 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 



Fig. 72. — Hyoid bones of a 

 goose, nat. size ; by Dr. E. W. 

 Shufeldt, U. S. A. a, car- 

 tilaginous end-piece of b, the 

 great glosso-liyal, which has 

 absorbed or replaced cerato- 

 hyals or " lesser cornua " ; c, 

 basihyal, movably articulated 

 with b, .and combined com- 



