182 ON THE STRUCTURE OF THE SKULL. 



The hyoidean arch consists of two median bones, — an an- 

 terior, the " entoghssal" which supports the tongue ; and a 

 posterior, the " urohyal" Its lateral cornua are formed by 

 four bones, two small (basi-hyal), and two large (ejri and 

 cerato-liyals) on each side, the latter supporting the "bran- 

 chiostea'al rays' ! on which the branchiosteoal membrane is 

 spread out ; and the upper of the two larger bones is con- 

 nected with the synchondrosis between the hyomandibular and 

 symplectic by a styliform bone — the stylo-hyal (Fig. 71, By.). 

 Thus, the hyomandibular may be regarded as common to the 

 mandibular and the hyoidean arches, supporting the former, 

 indirectly, by means of the symplectic, and the latter directly, 

 by means of the stylo-hyal. 



The stylo-hyal very probably corresponds with the styloid 

 process and pyramid of Man, but it is difficult to find any very 

 sure footing for our interpretations beyond this point. 



The manner in which the symplectic is connected, on the 

 one hand, with the representative of the incus, and, on the other 

 hand, with that of the styloid process and pyramid, is strongly 

 suggestive of a relation between this bone and the stapes. But 

 it must no less be admitted that similar arguments might be 

 used in favour of the stapedial character of the hyomandibular 

 bone, the articulation of which with the pro-otic and opisthotic 

 might be compared with the fitting in of the stapes into the 

 fenestra ovalis, which is bounded by these two bones ; or again, 

 plausible arguments might be brought forward in favour of the 

 view that the hyomandibular, at any rate, is a bone special to 

 fishes. At present, it may be well merely to indicate these 

 various possibilities, as the study of development has hardly 

 been carried sufficiently far to enable us to decide in favour of 

 one rather than of another. 



Each of the four anterior branchial arches is composed of 

 four bones, and the branchial arches of opposite sides are united 

 by connecting cartilages and median ossifications. The anterior 

 or first arch, which corresponds with the greater conm of the 

 hyoid of Man, is fixed to the pro-otic bone, between the exits of 

 the trigeminal and the portio dura, by cartilage. The succeeding 

 arches have no osseous or cartilaginous representatives in Man. 



