414 



HEAD AND NECK 



Crico-thyreoid ligament 



the strong central part the thyreo-hyoid membrane is attached 

 below to the upper margin of the lamina of the thyreoid 

 cartilage, and above to the deep aspect of the great cornu of 

 the hyoid bone. It is pierced by the internal laryngeal nerve 

 and superior laryngeal vessels. The lateral thyreo-hyoid 

 ligament, which forms the posterior border of the membrane, 

 on each side, is rounded and cord-like, and is composed chiefly 

 of elastic fibres. It extends from the tip of the great cornu 

 of the hyoid bone to the extremity of superior cornu of the 

 thyreoid cartilage. In this ligament there is usually developed 



a small oval cartilaginous 

 or bony nodule, which is 

 termed the cartilago triticea. 

 Musculus Cric o- 

 thyreoideus. The crico- 

 thyreoid muscle is placed 

 on the side of the cricoid 

 cartilage, and bridges over 

 the lateral portion of the 

 crico - thyreoid interval. 

 Taking origin from the 

 lower border and outer 

 surface of the arch of 

 the cricoid cartilage, its 

 fibres spread out in an 

 upward and posterior 

 direction, and are inserted 

 into the inner aspect of 

 the lower margin of the 

 thyreoid lamina, and also into the anterior border of its 

 inferior cornu. As a general rule, it is divided into two parts. 

 The anterior or oblique part is composed of those fibres which 

 are attached to the lamina of the thyreoid cartilage ; the 

 posterior or straight part is formed of those fibres which are 

 inserted into the inferior cornu of the thyreoid cartilage. It 

 is closely associated with the inferior constrictor muscle. The 

 crico-thyreoid muscle is supplied by the external laryngeal 

 branch of the superior laryngeal nerve. 



Conus Elasticus. Extending upwards, from the upper 

 border of the anterior and lateral parts of the cricoid cartilage 

 to the thyreoid and arytaenoid cartilages, is a strong elastic 

 membrane, the conus elasticus, which is separable into a 



FIG. 161. The Crico-thyreoid Muscle. 



