136 . REPORT — 1870. 



Oil the Connexion of tJie Hi/oid Arcli with the Cranium, 

 B>j Professor W. H. Flo^\-ee, F.E.S. 



In tlie sheep, as is well known, the anterior arch or cornu of the hyoidean appa- 

 ratus is described as consisting of three hones, of which the uppermost is by far 

 the largest and most important, and has received the name of stylo-hyal. This 

 bone is long, compressed, and at the proximal end enlarges and divides into two 

 short branches^ by the anterior of which it is continued as a cartilaginous band to 

 the cranium. The upper end of this band is again ossified in the form of a curved 

 cylindrical plug of bone, with a truncated lower extremity, lying in a groove ou 

 the side of the tympanic bone, the edges of which groove meet around it in adult 

 animals, aud often become anchylosed with it ; but this is only a secondary con- 

 nexion. The primary connexion is with the periotic or petro-mastoid bone, imme- 

 diately in front and to the inner side of the stylo-mastoid foramen. In embryonic 

 specimens it can be traced as a distinct band of cartilage lying to the anterior aud 

 inner side of the lower end of the Fallopian aqueduct, and passing to the upper 

 and back part of the tympanic cavity, near to the spot from which the stapedius 

 muscle takes origin. This is, then, the true proximal extremity of the anterior arch 

 of the hyoidean apparatus, if we leave out of consideration the stapedius and incus, 

 which, there is reason to believe, are developed from the same rod of cartilage — a 

 question which is not discussed in the present communication. Whatever may be 

 the case with regard to the origin of the last-named parts, it is a subject of easy 

 demonstration that in the sheep there is an ossified portion of the upper end of the 

 hyoid arch, above and distinct from the stylo-hyal, which becomes firmly united 

 with the periotic, and which may ossify either from a separate centre, or by ex- 

 tension of bone from the periotic. "Whether it should be considered as a process 

 of the periotic, or as a separate element, may still be a matter of opinion ; but the 

 existence of such a part as a distinct portion of the hyoid arch requires recognition. 

 It may be conveniently distinguished by the name of tympano-hnal, as it is always 

 in relation with the tympanic bone^ and continues the hyoid arch up to the wall 

 of the cavity of the tj-mpanum. 



This portion of the skull can be distinctly recognized at the spot indicated (»'. e. 

 to the anterior and inner side of the stj'lo-mastoid foramen) in almost aU mammals, 

 though in Aery different degrees of development, usually in accordance with the 

 size and amount of ossification of the remainder of the anterior arch. Thus, in 

 those of the Ungulata, as the ruminants, and especially the horse and rhinoceros, 

 in which the stylo-hyal is very largely developed, the tympano-hyal is most con- 

 spicuous ; but where, as in the pig, the anterior arch is little ossified, the tympano- 

 hyal is comparatively rudimcntaiy. In the Cetacea it is quite distinct, though 

 small, and a fine band of cartilage can often be traced from the upper end of the 

 stylo-hyal into it, imbedded in the great ligamentous mass wliicii attaches that 

 bone to the exoccipital and surroimding parts of the cranimn, and which of course 

 is only a secondaiy connexion. 



In man this bone or process is also quite distinct, although it seems to have 

 been generally confounded with the stylo-hyal. The so-called styloid process of 

 the temporal bone has long been known to have a separate centre of ossification, 

 and is also generally recognized as the homologue of the stylo-hyal of other mam- 

 mals, one of the main points of difl'erence being, that whereas in all others it is an 

 independent bone not connected directly with the cranium, in man it is always 

 anchylosed to the " temporal," and forms a process of the skull. 



If a human skull at the period of birth is examined, a very small round piece 

 of bone sm-rounded by a deep groove can be seen exactly where the tympano-hjal 

 is foimd in the sheep, just behind the posterior limb of the inverted arch fonned 

 bj' the tv-mpanic bone, and in front and to the inner side of the stylo-mastoid 

 foramen. This increases somewhat in size as age advances, fomiing a distinct 

 process, supported and partly embraced in front by the vaginal process of the 

 tympanic. The true styloid or stylo-hyal at birth is a slender rod of cartilage, 

 often partially ossified in the centre, and invested by a strong fibrous sheath, from 

 which the stylo-hyoid, stylo-glossus, and stylo-pharyngeus muscles take origin. 

 Thou.a-h it occasionally becomes anchylosed in the adult with the tjTnpano-hyal, as 



