THE HYOID BONE. 143 
The body (basis) is arched from side to side and compressed from before back- 
wards, so that its surfaces slope downwards and forwards. Its anterior surface 
displays a sight median ridge, on either side of 
which the bone is marked by the attachment (J i a 
of muscles. Its posterior surface, deeply hollowed, \~ 
is concave from side to side and from above down- 
wards. Herein he a quantity of fat and a bursa 
which separates this aspect from the thyro-hyoid 
membrane. The upper border is broad; it is 
separated from the anterior surface by a transverse 
ridge, behind which are the impressions for the 
attachment of the genio-hyoid muscles. Its 
hinder edge is thin and sharp; to this, above, are 5... 435 ‘Tam Hyorp Bonz AS SEEN 
attached the genio-glossi, whilst behind and below Syn TTD DE Oma 
the thyro-hyoid membrane is connected with it. 
The inferior border is well defined and narrow; it serves for the attachment of the 
omo-hyoid, sterno-hyoid, and thyro-hyoid muscles. 
The great cornua are connected on either side with the lateral parts of the 
body. At first, union is effected by synchondroses, which, however, ultimately 
ossify. These cornua curve backwards as well as upwards, and terminate in more or 
less rounded and expanded extremities. Compressed laterally, they serve for the 
attachments externally of the thyro-hyoid and hyoglossi muscles, and the middle 
constrictor of the pharynx from below upwards, whilst internally they are con- 
nected with the lateral expansions of the thyro-hyoid membrane, the free edges of 
which are somewhat thickened, and connect the extremities of the great cornua 
with the ends of the superior cornua of the thyroid cartilage below. 
The lesser cornua, frequently cartilaginous in part, are about the size of grains 
of wheat. They rest upon the upper surface of the bone at the junctions of the 
great cornua with the body. In youth they are separated from, but in advanced 
life become ossified with, the rest of the bone, from which they are directed upwards, 
backwards, and a little outwards. Their summits are connected with the stylo- 
hyoid ligaments; they also serve for the attachment of muscles. 
Small cornua 
Connexions.—The hyoid is slung from the styloid processes of the temporal bones by the 
stylo-hyoid hgaments. Inferiorly it is connected with the thyroid cartilage of the larynx by 
the thyro-hyoid ligaments and membrane. Posteriorly it is intimately associated with the 
epiglottis. 
Ossification.—In considering the development of the hyoid bone it is necessary to 
refer to the arrangement and disposition of the cartilaginous bars of the second and third 
visceral arches. That of the second visceral arch, the hyoid bar—or Reichert’s cartilage, 
as it is sometimes called—is united above to the petrous temporal, whilst ventrally it is 
joined to its fellow of the opposite side by an independent mesial cartilage. Chondrifica- 
tion of the third visceral arch only occurs towards its ventral extremity, forming what is 
known as the thyro-hyoid bar. This also unites with the mesial cartilage above mentioned. 
In these cartilaginous processes ossific centres appear in certain definite situations. 
Towards the end of feetal life a single centre (by some authorities regarded as primarily 
double) appears in the mesial cartilage, and forms the body of the bone (basihyal). 
About the same time ossification begins in the lower ends of the thyro-hyoid bars, and 
from these the great cornua are developed (thyro-hyals). During the first year the lower 
ends of the hyoid bars begin to ossify and form the lesser cornua (cerato-hyals). The 
cephalic ends of the same cartilages meanwhile ossify to form the styloid processes (stylo- 
hyals), (see p. 117), whilst the intervening portions of cartilage undergo resorption and 
become converted into the fibrous tissue of the stylo-hyoid ligaments, which in the adult 
connect the lesser cornua with the styloid processes of the temporal bone. The great 
cornua fuse with the body in middle life; the lesser cornua only at a more advanced 
period. Variations in the course of development lead to interesting anomalies of the 
hyoid apparatus. The lesser cornua may be unduly long or the stylo-hyoid ligament may 
be bony ; in this case the cartilage has not undergone resorption, but has passed on to the 
further stage of ossification, thus forming an epihyal element comparable to that in the 
dog. The ossified stylo-hyoid ligament, as felt through the pharyngeal wall, may be 
mistaken for a foreign body. (Farmer, G. W.8., Brit. Med. Journ. 1900, vol. i. p. 1405.) 
