THE CAVITY OF THE CHEST. 31 



tained. We see, then, that the hollows of the face contain the various 

 organs of the senses. 



On the sides of the face and neck, behind and below the lower jaw, 

 are four more salivary glands, two on each side, the parotid and sub- 

 maxillary (see Fig. 14), certain ducts or tubes from which convey the 

 saliva which they secrete into the mouth. 



In the neck, which is interposed between the head and the chest, 

 there is no regularly defined and protected cavity, but certain impor- 

 tant parts are found there, passing downwards from the pharynx, to 

 reach the chest. Immediately beneath the root of the tongue, just at 

 the re-entering angle of the neck, is situated the little lingual or hyoid, 

 i. e., y-shaped bone (shown in section at h, Fig. 9), which helps to 

 support the tongue. Suspended to this hyoid bone, is a hollow carti- 

 laginous organ, corresponding with the prominence of the throat, called 

 the larynx^ I. This is the organ of the voice ; it communicates above 

 with the pharynx, by means of a slit-like aperture, called the glottis, 

 which is protected by a flap or valve, named the epiglottis, e ; below, 

 the larynx opens freely into the windpipe or trachea, which passes 

 down into the chest, Fig. 15, t, to branch into the lungs, and is known 

 by the numerous cartilaginous rings, which enter into its construction, 

 and keep it constantly open. Behind the larynx, the pharynx, p, 

 becomes continuous with a membranous tube, called the gullet or oeso- 

 phagus, Fig. 15, o, which also passes down behind the wind-pipe, and 

 in front of the bodies of the cervical vertebrae into the chest, and thence 

 on into the abdomen, to end in the stomach, as we shall presently see. 



b. The chest or thorax is not, like the cranium, a complete osseous 

 box, but rather an open cage-work of bones, consisting of the dorsal 

 part of the spine, the twenty-four ribs, and the sternum, Fig. 10, the 

 intervals between which' are occupied with muscles, membranes, ves- 

 sels, and other soft parts. It therefore admits of certain essential 

 alterations of its size. The thorax is conical in form, being narrowest 

 above, where it is closed chiefly by the tubes and vessels passing into 

 or out of it from or to the neck, and widest below, where it is separated 

 from the other large cavity of the trunk, the abdomen, by a vaulted 

 partition, partly muscular and partly tendinous, called the diaphragm, 

 Fig. 14, d, which springs from the spine, and is inserted into the lower 

 borders of the cartilages of the seventh and the succeeding ribs, and 

 into the tip of the sternum, all of which parts are represented as being 

 preserved in Fig. 13, to show the boundary between the opened chest 

 and abdomen. The interior of the thorax is divided by membranes 

 into three compartments : thus, on each side is a large compartment 

 marked off and lined throughout by a thin, continuous, and" moist 

 serous membrane, called the pleura, which forms a completely closed 

 sac, so that there are two pleurce, or two distinct pleural sacs, one right 

 and the other left. The right lung occupies the right pleural sac, and 

 the left lung the left pleural sac, as may be seen in the annexed draw- 

 ing, Fig. 13. The cut edge of the right pleura is distinctly seen on 

 the inner side of the right lung. The lungs, I I, are attached only at 

 their roots, which are found at their posterior borders ; everywhere else 

 they are covered with a layer of their corresponding pleura, which is 



