238 PROFESSOR TURNER'S ACCOUNT OF THE GREAT FINNER WHALE 



powerful sphincter for closing the glottis during deglutition. A deeper set 

 of fibres of the same muscle was exposed by the removal of the thyro-hyoid 

 membrane. 



There were no true vocal cords passing from the thyroid to the arytenoid 

 cartilages, or laryngeal ventricles, but a slight fold of the mucous membrane, 

 extended obliquely in the antero-posterior direction within the aperture of the 

 glottis, on each side, a short distance below the free edge of the aryteno- 

 epiglottidean folds. These might, perhaps, be regarded as rudimentary false 

 vocal cords. 



One of the most interesting structures connected with the larynx was the 

 great laryngeal pouch or cul-de-sac. It was 10 inches in length in the foetus, and 

 extended backward from the thyroid cartilage, in close relation to the ventral 

 surface of the inferior crico-tracheal membrane, to within 2 inches from the 

 bifurcation of the trachea. Its outer wall was formed by a powerful muscle, 

 which arose from the superior surface of the median tongue and adjacent lateral 

 plate of the thyroid, from the inferior free border of the cricoid, and from the 

 body of the arytenoid. The fibres were arranged in transverse rings around 

 the walls of the pouch, and they formed a thick mass at its posterior end. The 

 pouch was lined by a mucous membrane, which was continuous with the general 

 mucous lining of the larynx, by extending upwards on the inner surface of the 

 bodies of the arytenoid cartilages, and by passing round the free border of the 

 hoop formed by their posterior horns. The mouths of numerous large crypts 

 opened on the surface of this membrane. 



Owing to the peculiar arrangement of the arytenoid cartilages and the 

 presence of this pouch, the laryngeal chamber might be regarded as subdivided 

 into three compartments. The supero-anterior which formed the glottis proper, 

 was bounded by the epiglottis, the aryteno-epiglottidean folds, and the anterior 

 horns and bodies of the arytenoid cartilages with their investing and intermediate 

 mucous membrane. The posterior was bounded above and to the sides by the 

 cricoid cartilage, in front by the two posterior horns of the arytenoids, which 

 ran obliquely from above backwards and downwards ; through the fissure 

 between these horns it communicated with the glottis, whilst behind it was con- 

 tinuous with the canal of the trachea. The inferior was the laryngeal pouch 

 above described, which communicated directly and freely with the glottis at 

 the base of the epiglottis, but with the posterior chamber through the fissure 

 between the arytenoid horns. This pouch is often regarded as occasioned by a 

 deficiency in the ventral part of the ring of the cricoid cartilage. But from 

 the description of the arrangement of these parts, and from the figure 37, it 

 will be seen that although this plate of cartilage is defective, yet that the ring 

 is completed ventrally by the strong inferior crico-tracheal fibrous membrane, 

 beneath which the pouch is situated. The laryngeal sac is rather to be regarded 



