DISSECTION OF THE DOG 177 



sterno-thyroid, and thyro-hyoid muscles. Take care to preserve the 

 laryngeal nerves and vessels. Now examine the structures on the 

 ventral aspect of the larynx. 



Ligamentum hyo-thyreoideum. — The connection of the hyoid hone and 

 the thyroid cartilage is established by a continuity of the extremities of the 

 thyro-hyals with the oral thyroid cornua, and by the presence of a membranous 

 hyo-thyroid ligament. This ligament, which fills the gap between the hyoid 

 bone and the thyroid cartilage, is attached on the one hand to the body and 

 thyroid processes of the hyoid bone, and on the other to the oral border of the 

 thyroid laminae. Strongest in the middle line, it becomes thinner laterally 

 where it is pierced by the superior laryngeal nerve. > 



M. crico- thyreoideus. — The crico-thyroid muscle lies on the side of the 

 cricoid arch, from the aboral border and the lateral surface of which it takes its 

 origin. The insertion of the muscle is into the aboral border and immediately 

 adjacent parts of both surfaces of the lamina as well as the aboral cornu of 

 the thyroid cartilage. 



Ligamentum crico-thyreoideum. — In the triangular gap between the 

 two crico-thyroid muscles a strong ligamentous band, the crico-thyroid liga- 

 ment, will be observed. The broader end of the ligament is attached to the 

 margins of the shallow caudal thyroid notch, while the narrower end is fixed 

 to the mid-ventral part of the cricoid cartilage. Laterally the ligament is 

 continuous with a thin membrane which will be exposed later. 



The articulation between the thyroid cornu and the cricoid cartilage should 

 be looked at now, but its complete examination may be deferred until the 

 dissection of the larynx nears completion. The joint is a diarthrosis provided 

 with the usual joint-capsule attached round the articular margins of the two 

 cartilages. 



