THE LARYXX. ITS CARTILAGES. 905 



whole extent of the thoracic wall, where it is covered with the pleural membrane. 

 At the same time, their previously thin sharp margins become more obtuse, and their 

 whole form is less compressed. 



2. Consistence, texture, and colour. The introduction of air and of an increased 

 quantity of blood into the foetal lungs, which ensues immediately upon birth, con- 

 verts their tissue from a compact, heavy, granular, yellowish-pink, gland-like substance, 

 into a loose, light, rose-pink, spongy structure, which, as already mentioned, floats in 

 water. The changes thus simultaneously produced in their consistence, colour, and 

 texture, occur first at their anterior borders, and proceed backwards through the lungs : 

 they, moreover, appear in the right lung a little sooner than in the left. 



3. Weight. The absolute weight of the lungs, having gradually increased from the 

 earliest period of development to birth, undergoes at that time, from the quantity of 

 blood then poured into them, a very marked addition, amounting to more than one- 

 third of their previous weight : for example, the lungs before birth weigh about one and 

 a half ounce, but, after complete expansion by respiration, they weigh as much as two 

 and a half ounces. The relative weight of the lungs to the body, which at the termi- 

 nation of intra-uterine life is about 1 to 70, becomes, after respiration, on an average, 

 about 1 to 35 or 40 ; a proportion which is not materially altered through life. 

 Their specific gravity is at the same time changed from 1'056 to about '342. 



4. Changes in the trachea after birth. In the foetus the trachea is flattened before 

 and behind, its anterior surface being even somewhat depressed ; the ends of the car- 

 tilages touch ; and the sides of the tube, which now contains only mucus, are applied 

 to one another. The effect of respiration is at first to render the trachea open, but 

 it still remains somewhat flattened in front, and only later becomes convex. 



THE LARYNX, OR ORGAN OF VOICE. 



The upper part of the air-passage is modified in its structure to form the 

 organ of voice. This organ, named the larynx, is placed at the upper and 

 fore part of the neck, where it forms a considerable prominence in the 

 middle line. It lies between the large vessels of the neck, and below the 

 tongue and os hyoides, to which bone it is suspended. It is covered in 

 front by the cervical fascia along the middle line, and on each side by the 

 steruo-hyoid, sterno- thyroid, and thyro-hyoid muscles, by the upper end of 

 the thyroid body, and by a small part of the inferior constrictor of the 

 pharynx. Behind, it is covered by the pharyngeal mucous membrane, and 

 above it opens into the cavity of the pharynx. 



The larynx consists of a framework of cartilages, articulated together 

 and connected by proper ligaments, two of which, named the true vocal 

 cords, are more immediately concerned in the production of the voice. It 

 also possesses muscles, which move the cartilages one upon another, and 

 modify the form and tension of its apertures, a mucous membrane lining its 

 internal surface, numerous mucous glands, and lastly, blood-vessels, 

 lymphatics, and nerves, besides areolar tissue and fat. 



Cartilages of the Larynx. 



The cartilages of the larynx consist of three single and symmetrical 

 pieces, named respectively the thyroid cartilage, the cricoid cartilage, and 

 the cartilage of the epiglottis, and of six others, which occur in pairs, 

 namely, the two arytenoid cartilages, the cornicula laryngis, and the cunei- 

 form cartilages. In all there are nine distinct pieces, the two coruicula and 

 two cuneiform cartilages being very small. Of these, only the thyroid and 

 cricoid cartilages are seen on the front and sides of the larynx ; the aryte- 

 noid cartilages, surmounted by the cornicula laryngis, together with the 

 back of the cricoid cartilage, on which they rest, form the posterior wall of 



