THE LARYNX 413 



aspect of the cricoid cartilage. It is through the anterior wall 

 of this gompartrnent that the opening is made in the operation 

 of laryngotomy. 



Mucous Membrane of the Larynx. This is continuous 

 above with that lining the pharynx, and below with the 

 mucous lining of the trachea. Over the laryngeal or posterior 

 surface of the epiglottis it is closely adherent, but elsewhere, 

 above the level of the vocal folds, it is loosely attached by 

 submucous tissue. As it passes over the vocal folds it is very 

 thin and tightly bound down, and in inflammatory conditions 

 of the larynx, attended by oedema, this attachment usually 

 prevents the infiltration of the submucous tissue from extend- 

 ing downwards below the rima glottidis. 



The mucous membrane of the larynx has a plentiful supply 

 of racemose glands which secrete mucus. Over the surface 

 of the vocal folds these are completely absent. 



Dissection. Place the larynx upon a block so that its anterior surface 

 looks upwards, and fix it in that position with pins. The branches which 

 the external laryngeal nerve gives to the crico-thyreoid muscle should in the 

 first place be followed out ; and, carefully preserving the superior and inferior 

 laryngeal vessels and the internal and inferior laryngeal nerves, the dis- 

 sector should in the next place proceed to remove the thyreoid gland, and 

 the omo-hyoid, sterno- hyoid, sterno-thyreoid, and thyreo-hyoid muscles. 

 The fibres of origin of the inferior constrictor muscle also should be 

 cleared away from the thyreoid and cricoid cartilages. The broad thyreo- 

 hyoid membrane, the crico-thyreoid ligament, and the crico-thyreoid 

 muscles are now exposed, and their attachments may be defined. 



Membrana Hyo-thyreoidea. This is a broad membranous 

 sheet, which occupies the interval between the hyoid bone 

 and the thyreoid cartilage. It is not equally strong throughout, 

 but shows a central thick portion, the median thyreo-hyoid 

 ligament, largely composed of elastic fibres, and cord -like 

 right and left margins, the lateral thyreo-hyoid ligaments, 

 whilst in the intervals between the central part and the 

 lateral margins it is thin and weak. The median ligament is 

 attached above to the posterior aspect of the upper margin of 

 the body of the hyoid bone ; below, it is fixed to the sides of 

 the deep median notch which interrupts the superior border of 

 the thyreoid cartilage. The upper part of its anterior surface is, 

 therefore, placed posterior to the posterior hollowed-out surface 

 of the body of the hyoid bone ; a mucous bursa is interposed 

 between them, and in certain movements of the head and 

 larynx the upper border of the thyreoid cartilage is allowed 

 to slip upwards posterior to the hyoid bone. On each side of 



