332 ELEMENTARY PHYSIOLOGY. [XXXI. 



2. From the posterior surface carefully remove the 

 oesophagus with the pharyngeal muscles. From 

 the sides dissect away the sterno-thyroid muscle 

 (Lesson I. p. 22), taking care not to injure the 

 muscle lying underneath it ( 3), and clear away 

 the whole of the thyro-hyoid muscle which 

 covers the side of the thyroid. The hyoid bone 

 and thyro-hyoidean membrane may be left. 

 The outlines of the thyroid will now come into 

 view, clear away the connective tissue until they 

 are quite distinct. Note that 



The thyroid cartilage consists of two lateral 

 lamina?, which meet in front and diverge behind, 

 and have their upper and lower posterior angles 

 prolonged, forming the upper and lower cornua. 

 Observe in front the rounded projection or 

 Adam's apple. 



3. Observe the crico-thyroid muscle spoken of 

 above ( 2); dissect it away, noting its attach- 

 ments. The cricoid cartilage will come into 

 view, and it will be seen that the muscle in 

 question passes from the posterior cornu and 

 posterior portion of the lower margin of the 

 thyroid, to the front part of the cricoid. Observe 

 that below this muscle there is stretching be- 

 tween the two cartilages a membrane which 

 limits the movements of the thyroid. 



4. Observe the articulations of the posterior cornua 

 of the thyroid to the cricoid. Disarticulate one 

 cornu, cut through the crico-thyroid membrane, 



