THE HYOID BDSE. 



227 



THE HYOID BONE. 



The Hyoid bone is named from its resemblance to the Greek upsilon ; it is 

 also called the lingual bone, because it supports the tongue and gives attachment 

 to its numerous muscles. It is a bony arch, shaped like a horseshoe, and 

 consisting of five segments, a 



O 



body, two greater cornua, and 

 two lesser cornua. It is sus- 

 pended from the tip of the sty- 

 loid processes of the temporal 

 bone by ligamentous bands, the 

 tfylo-kyoid ligaments. 



The Body (basi-hyaT) forms 

 the central part of the bone, and 

 is of a quadrilateral form ; its 

 anterior surf aw (Fig. 178), con- 

 vex, directed forward and upward. 



THYRO-MYOIO. 

 STYLO-HYOIO. 



Body. 



zv; - : : 



MYLO-HYOID. 



QENIO-HYOID. 



STERNO-HYOIO. 



FIG. 178. Hyoid bone. Anterior surface. (Enlarged). 



is divided into two parts by a 

 vertical ridge which descends 

 along the median line, and is 

 crossed at right angles by a hori- 

 zontal ridge, so that this surface is divided into four spaces or depressions. At 

 the point of meeting of these two lines is a prominent elevation, the tubercle. 

 The portion above the horizontal ridge is directed upward, and is sometimes 

 described as the superior border. The anterior surface gives attachment to the 

 Genio-hyoid in the greater part of its extent ; above, to the Genio-hyo-glossus : 

 below, to the Mylo-hyoid, Stylo-hyoid, and aponeurosis of the Digastric 

 (suprahyoid aponeurosis) ; and between these to part of the Hyo-glossus. 

 The posterior surface is smooth, concave, directed backward and downward, 

 and separated from the epiglottis by the thyro-hyoid membrane and by 

 a quantity of loose areolar tissue. The superior border is rounded, and 

 gives attachment to the thyro-hyoid membrane, part of the Genio-hyo-glossi and 

 Chondro-glossi muscles. The inferior border gives attachment, in front, to the 

 Sterno-hyoid : behind, to the Omo-hyoid and to part of the Thyro-hyoid at its 

 junction with the great cornu. It also gives attachment to the Levator glandulae 

 thyroideae when this muscle is present. The lateral surfaces are small, oval, con- 

 vex facets, covered with cartilage for articulation with the greater cornua. 



The Greater Cornua (thyro-hyat) project backward from the lateral surfaces of 

 the body : they are flattened from above downward, diminish in size from before 

 backward, and terminate posteriorly in a tubercle for the attachment of the lat- 

 eral thyro-hyoid ligament. The outer surface gives attachment to the Hyo-glos- 

 sus. their upper border to the Middle constrictor of the pharynx, their lower bor- 

 der to part of the Thyro-hyoid muscle. In youth the great cornua are connected 

 to the body by cartilaginous surfaces and held together by ligaments ; in middle 

 life they usually become joined. 



The Lesser Cornua (cerato-hyals) are two small, conical-shaped eminences 

 attached by their bases to the angles of junction between the body and greater 

 cornua. and giving attachment by their apices to the stylo-hyoid ligaments. 1 The 

 smaller cornua are connected to the body of the bone by a distinct diarthrodial 

 joint, which usually persists throughout life, but occasionally becomes ankylosed. 



Development. By jive centres : one for the body, and one for each cornu. 

 ncation commences in the body about the eighth month, and in the greater 

 cornua toward the end of foetal life. Ossification of the lesser cornua commences 

 some months after birth. 



Attachment of Muscles. Sterno-hyoid, Thyro-hyoid, Omo-hyoid, aponeurosis 



1 These ligaments in many animals are distinct bones, and in man are occasionally ossified to a 

 certain extent. 



