THE LARYNX 415 



median and two lateral parts. The median part is the crico- 

 thyreoid ligament which extends from the upper border of the 

 anterior part of the cricoid arch to the lower border of the 

 thyreoid cartilage. Each lateral part (O.T. lateral part of 

 crico-thyreoid membrane) runs upwards and medially and 

 terminates in a free thickened border, the ligamentum. vocale, 

 which lies in the substance of the plica vocalis and is 

 attached posteriorly to the vocal process of arytaenoid, and 

 anteriorly to the angle of union of the two laminae of the 

 thyreoid cartilage. The inner surface of the conus elasticus 

 is covered with the mucous membrane of the lowest section of 

 the cavity of the larynx, and the outer surface is in relation 

 with the lateral crico-arytaenoid and the vocalis muscles. 



Dissection. The position of the larynx must now be reversed. Fix 

 it upon the block in such a manner that its posterior aspect is directed 

 upwards. The oesophagus should then be slit open by a median incision 

 through its posterior wall. Next remove the mucous membrane which 

 covers the posterior aspect of the cricoid and arytsenoid cartilages. In 

 doing this, bear in mind that the inferior laryngeal artery and the inferior 

 laryngeal nerve pass upwards, between the thyreoid and cricoid cartilages, 

 and must be preserved. 



Upon the posterior aspect of the broad lamina of the cricoid cartilage 

 the dissector will now note the two posterior crico-arytaenoid muscles, and 

 the attachment of the tendinous band through which the longitudinal fibres 

 of the oesophagus are fixed to the cricoid cartilage. The band takes origin 

 from the prominent median ridge on the posterior aspect of the cricoid 

 cartilage. On the posterior surface of the arytaenoid cartilages, and bridg- 

 ing across the interval between them, are the transverse and oblique parts 

 of the arytaenoid muscle. Especial care must be taken in cleaning this 

 muscle in order that the connections of the superficial decussating fibres 

 may be ascertained fully. 



The lateral layer of the right ary-epiglottic fold of mucous membrane 

 should now be cautiously removed. This will expose the ary-epiglottic 

 muscle, the cuneiform cartilage, and the corniculate cartilage of that side. 

 This is perhaps the most difficult part of the dissection, because the 

 dissector has to establish the continuity of the sparse fibres, which com- 

 pose the pale ary-epiglottic muscle, with the decussating fibres of the 

 arytaenoid muscle. 



Musculus Crico-Arytsenoideus Posterior. The posterior 

 crico-arytaenoid muscle is somewhat fan-shaped (Fig. 162). 

 It springs by a broad origin from the depression which marks 

 the posterior surface of the cricoid cartilage, on each side of 

 the median ridge, and its fibres converge to be inserted into 

 the posterior surface of the muscular process or projecting 

 lateral angle of the base of the arytaenoid cartilage. 



In pursuing this upward and lateral course, the fibres run with different 

 degrees of obliquity. The uppermost fibres are short and nearly horizontal ; 



