Part 39 (1/2)

590. The CRICOID CARTILAGE takes its name from its resemblance to a ring. It is situated below the thyroid cartilage, it is narrow in front, broader at the sides, and still broader behind, where it is connected with the thyroid cartilage. Below, it connects with the first ring of the trachea.

[Ill.u.s.tration: Fig. 102. A side view of the cartilages of the larynx. *

The front side of the thyroid cartilage. 1, The os hyoides, (bone at the base of the tongue.) 2, The ligament that connects the hyoid bone and thyroid cartilage. 3, 4, 5, The thyroid cartilage. 6, The cricoid cartilage. 7, The trachea.]

[Ill.u.s.tration: Fig. 103. A posterior view of the cartilages and ligaments of the larynx. 1, The posterior face of the epiglottis. 3, 3, The os hyoides. 4, 4, The lateral ligaments which connect the os hyoides and thyroid cartilage. 5, 5, The posterior face of the thyroid cartilage. 6, 6, The arytenoid cartilages. 7, The cricoid cartilage. 8, 8, The junction of the cricoid and the arytenoid cartilages. 12, The first ring of the trachea.]

589. Describe the thyroid cartilage. 590. From what does the cricoid cartilage derive its name? Where is it situated? Explain fig. 102.

Fig. 103.

591. The ARYTENOID CARTILAGES are small triangular bodies placed upon the back part of the cricoid cartilage. They are connected with the thyroid cartilages, by four ligaments, called _Vocal Cords_.

592. The EPIGLOTTIS is fibro-cartilaginous, and is placed behind the base of the tongue. In shape it resembles a leaf of parsley.

593. The VOCAL CORDS, or ligaments, are formed of elastic and parallel fibres, enclosed in a fold of mucous membrane. They are about two lines in width, and pa.s.s from the anterior angle of the thyroid cartilage, to the two arytenoid cartilages. The one is called the superior, and the other the inferior vocal ligament. The cavity, or depression between the superior and inferior ligament, is called the _ventricle_ of the larynx. The aperture, or opening between these ligaments, is called the _glottis_, or _c.h.i.n.k of the glottis_. It is about three fourths of an inch in length, and one fourth of an inch in width, the opening being widest at the posterior part. This opening is enlarged and contracted by the agency of the muscles appropriated to the larynx.

[Ill.u.s.tration: Fig. 104. An ideal, lateral section of the larynx. 1, 1, The upper vocal cords. 2, 2, The lower vocal cords. 3, 3, The glottis. 4, 4, The ventricles of the larynx.]

[Ill.u.s.tration: Fig. 105. A vertical section of the larynx. 2, The os hyoides. 4, The apex of the epiglottis. 7, The superior vocal ligament.

9, The ventricle of the larynx. 10. The lower vocal ligament. 11, The arytenoid cartilage. 12, 13, The cricoid cartilage. 14, The trachea. 18, The oesophagus.]

591. Describe the arytenoid cartilages. 592. What is said of the epiglottis? 593. Give the structure of the vocal cords. Where is the ventricle of the larynx? Where is the glottis situated? What is represented by fig. 104? Explain fig. 105.

[Ill.u.s.tration: Fig. 106. A view of the larynx from above, showing the vocal ligaments. 1, The anterior edge of the larynx. 4, The posterior face of the thyroid cartilage. 5, 5, The arytenoid cartilages. 6, 6, The vocal ligaments. 7, Their origin, within the angle of the thyroid cartilage. 9, Their termination, at the base of the arytenoid cartilages.

8, 10, The glottis.]

594. The larynx is connected by muscles with the sternum, oesophagus, base of the skull, hyoid bone, lower jaw, and tongue. This organ is supplied with a large number of blood-vessels, and it likewise receives nerves from the sympathetic system, and two large nerves from the tenth pair. The number and size of the nervous filaments distributed to the mucous membrane of the larynx, render it more sensitive than any other portion of the respiratory organs.

How is the glottis enlarged or contracted? Explain fig. 106. 594. By what means and to what organs is the larynx connected? Why is the larynx more sensitive than other parts of the respiratory organs?

595. The larynx is much more developed and prominent in man than in woman. In the former, the anterior angle of the thyroid cartilage is acute, while in the latter it is rounded, and the central slope of the superior border of the same cartilage is less deep, and the epiglottis smaller and less prominent, than in man.

596. The difference in the formation of the larynx in infancy is less striking; but at a later period, it is more developed in the male than in the female. It is very remarkable that this increase is not progressive, like that of other organs, but, on the contrary, develops itself at once at the period of p.u.b.erty.

PHYSIOLOGY OF THE VOCAL ORGANS.