400 



MAMMALIAN ANATOMY 



the addition of a piece of cartilage, which turns downward to join the 

 posterior upper part of the thyroid cartilage of the larynx (Fig. 316). 

 This piece has been called the chondro-hyal. The thyro-hyal is 

 united in front by cartilage to the basi-hyal and cerato-hyal and by 

 a strong membrane from its lower border to the thyroid cartilage. 

 It furnishes attachment to the thyro-hyoid muscle. 



FIG. 316. 



Tympano-hyal 



Stylo-hyal. 



Epi-hyal. 



Basi-hyal. 



Chondro-hyal. 



Cerato-hyal. 

 Thyro-hyal. 



Thyroid Cartilage. 



Cricoid Cartilage. - 



HYOID BONES AND LARYNX. LEFT SIDE. 



The basi-hyal is not so long as the epi-hyal. It is straight, and 

 presents upper and lower surfaces which furnish attachment to the 

 genio-hyoid and sterno-hyoid muscles. Its ends are slightly enlarged 

 and are joined by intermediate cartilages to the thyro-hyals. The 

 basi-hyal also is united to the thyroid cartilage by membrane. 



The hyoid apparatus is capable of not a little motion ; it is elevated 

 when the tongue is protruded, and alternately elevated and depressed 



in swallowing. 



VARIATIONS IN THE HYOID. 



An increase in the number of bony elements in the jointed anterior 

 bar appears to be not uncommon ; I have seen it in three specimens 

 out of twenty-five examined. In each case the increase was on the 

 right side only and was due to the interposition of a new element 

 between the cerato-hyal and the epi-hyal, and at their expense. The 

 additional bone was about half as long as a normal cerato-hyal. 



