154 SPECIAL ANATOMY OF THE SKELETON 



life are joined to the greater cornua. In early life they are connected with the 

 cornua by cartilaginous surfaces, and held together byligaments, and occasion- 

 ally a synovial membrane is found between them. 



Borders. The superior border is rounded, and gives attachment to the thyro- 

 hyoid membrane, part of the Geniohyoglossi and Chondroglossi muscles. The 

 inferior border gives attachment, in front, to the Sternohyoid; behind, to the Omo- 

 hyoid and to the part of the Thyrohyoid at its junction with the great cornua. 

 It also gives attachment to the Levator glandulae thyroideae when this muscle 

 is present. 



The Greater Cornua (cornua majorci), or thyrohyals, 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 lateral thyrohyoid ligament. The outer surface gives 

 attachment to the Hyoglossus, their upper border to the Middle constrictor of 

 the pharynx, their lower border to part of the Thyrohyoid muscle. 



The Lesser Gornua (cornua mmora), or ceratohyals, 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 stylohyoid 

 ligaments. 1 The smaller cornua are connected to the body of the bone by a 

 distinct diarthrodial joint, which usually persists throughout life, but occasion- 

 ally becomes ankylosed. 



Development. From six centres two (sometimes one) for the body, and one for each 

 cornu. Ossification commences in the body about the eighth month, and in the greater cornua 

 toward the end of fetal life. Ossification of the lesser cornua commences in the first or second 

 year after birth. 



Attachment of Muscles. Sternohyoid, Thyrohyoid, Omohyoid, aponeurosis of the 

 Digastric, Stylohyoid, Mylohyoid, Geniohyoid, Geniohyoglossus, Chondroglossus, Hyoglossus, 

 Middle constrictor of the pharynx, and occasionally a few fibres of the Inferior lingualis. It 

 also gives attachment to the thyrohyoidean membrane and the stylohyoid, thyrohyoid, and 

 hyoepiglottic ligaments. 



Surface Form. The hyoid bone can be felt in the receding angle below the chin, and the 

 finger can be carried along the whole length of the bone to the greater cornu, which is situated 

 just below the angle of the mandible. This process of bone is best perceived by making pressure 

 on one cornu, and so pushing the bone over to the opposite side, when the cornu of this side will 

 be distinctly felt immediately beneath the skin. This process of bone is an important landmark 

 in ligation of the lingual artery. 



Applied Anatomy. The hyoid bone is occasionally fractured, generally from direct vio- 

 lence, as in the act of garroting or throttling. It is frequently found broken in those who have 

 been hanged. The greater cornu is the part of the bone most frequently broken, but sometimes 

 the fracture takes place through the body of the bone. In consequence of the muscles of the 

 tongue having important connections with this bone, there is great pain upon any attempt being 

 made to move the tongue, as in speaking or swallowing. 



THE THORAX. 



The thorax, or chest, is an osseocartilaginous cage, the cavity of which (cavum 

 thoracis) contains and protects the principal organs of respiration and circula- 

 tion. It is conical in shape, being narrow above and broad below, flattened 

 from before backward, and longer behind than in front. It is somewhat reni- 

 form on transverse section. 



Boundaries. The posterior surface is formed by the twelve thoracic vertebra? 

 and the posterior part of the ribs. It is concave from above downward, and pre- 

 sents on each side of the middle line a deep groove, the vertebral groove, in conse- 

 quence of the direction backward and outward which the ribs take from their 



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



