283 THE LARYNX. 



The rinia glottidis, an elongated aperture, situated, anteriorly, 

 between the inferior or true vocal cords, and, posteriorly, between the 

 bases of the arytenoid cartilages, forms a long narrow slit, slightly 

 wider in the centre when nearly closed, as in the production of the 

 voice (fig. 191, a') ; when moderately ojien, as in easy respiration, its 

 shape is that of a long triangle, the pointed extremity being directed 

 forwards, and the base being behind, between the arytenoid car- 

 tilages (b) ; in its fully dilated condition it is lozenge-shaped (the pos- 

 terior sides being formed by the inner sides of the bases of the aryte- 

 noid cartilages), while the posterior angle is truncated (c). The rima 

 glottidis is the narrowest part of the interior of the larynx; in the 

 adult male it measures about eleven lines or nearly an inch in an 

 antero-posterior direction, and three or four lines across at its widest 

 part, which may be dilated to nearly half an inch. In the female, and 

 in males before the age of puberty, its dimensions are less, its antero- 

 posterior diameter being about eight lines, and its transverse diameter 

 about two. The vocal cords are about seven lines long in the adult 

 male, and five in the female. 



The ventricles, or sinuses of the larynx (fig. 190, s, and fig. 192, i'), 

 are narrower at their orifice than in their interior. The outer surface 

 of each is covered by the upper fibres of the corresponding thyro-aryte- 

 noid muscle. 



The small culs-de-sac named the laryngeal 2)oiiches (fig. 190,6-'), lead 

 from the anterior part of the ventricles upwards, for the space of half 

 an inch, between the superior vocal cords inside, and the thyroid 

 cartilage outside, reaching as high as the upper border of that cartilage 

 at the side of the epiglottis. The pouch is conical in shape, and 

 curved slightly backwards. Its opening into the ventricle is narrow, 

 and is generally marked by two folds of the lining mucous mem- 

 brane. Numerous small mucous glands, sixty or seventy in number, 

 open into its interior, and it is surrounded by a quantity of fat. Ex- 

 ternally to the fat, this little pouch receives a fibrous investment, which 

 is continuous below with the superior vocal cord. Over its laryngeal 

 side and upper end is a thin layer of muscular fibres (compressor sacculi 

 laryngis, arytceno-epiglottideus inferior, Hilton) connected above with 

 those found in the aryteno-epiglottidean folds. The upper fibres of the 

 thyro-arytenoid muscles pass over the outer side of the pouch, a few 

 being attached to its lower part. The laryngeal pouch is supplied 

 abundantly with nerves, derived from the superior laryngeal. 



MUSCLES OF THE LAEYNX. 



Besides certain extrinsic muscles elsewhere described — viz., the 

 sterno-hyoid, omo-hyoid, sterno-thyroid, and thjTO-hyoid muscles, 

 together with the muscles of the suprahyoid region, and the middle 

 and inferior constrictors of the pharynx, all of which act more or less 

 upon the entire larynx — there are certain mtrinsic muscles which move 

 the different cartilages upon one another, and modify the size of the 

 apertures and the state of tension of the soft parts. These intrinsic 

 muscles are the crico-tlnjroid, the posterior and lateral crico-aryfenoid, the 

 thyro-arytenoid, the arytenoid, and the arylejio-epiylottidcan, together 

 with certain other slender muscular fasciculi. All these muscles, except 

 the arytenoid, which crosses the middle line, are in pairs. 



