the median line of the chest), beginning at the base of the neck and reaching to the so-called "pit of the stomach" (Fig. XV, a) and the clavicle (Fig. XV, b, b).

Most of the ribs are connected with the sternum by cartilages.

The cavity (of the chest) formed in this way contains the heart and the lungs, and is divided from the abdominal cavity by a large muscle, the diaphragm, as has been described.

a, a, the dorsal vertebræ; b, b, the ribs; d, lumbar vertebræ; f, shoulder-blades.

By means of muscles and tendons, which surround the bony walls of the chest, these latter possess the

capacity to expand, and consequently to increase the thoracic cavity. Upon the degree of this power of expansion depends the size of the lungs, as they, being attached to the chest-walls by enclosing membranes (called pleura), can only expand in proportion to the increase of the thoracic cavity.

The functions of the chest, in respect to respiration, will be fully explained in Part IV.

SECTION 2.

THE ORAL CAVITY (FIG. XVII).

By the term "oral cavity" we understand the free space enclosed by the tongue, palate (soft-palate and uvula), and lips. It forms the entrance to the stomach and to the lungs, and contains the muscle most important to speech, the tongue, which is attached to the floor of the oral cavity.

The roof of the oral cavity is called the "palate," which consists of two portions, the anterior being named the bony or hard-palate, the posterior (from the centre of which depends the uvula), the softpalate. The hard-palate also composes the floor of the nasal cavity. The sides of the oral cavity are formed by the jaw-bones and the teeth. The tonsils are placed at the sides of the soft-palate.

The

opening (fauces), which lies between the soft-palate and the back part of the tongue, is of great importance during singing and speaking, as we shall see further on.

SECTION 3

THE NASAL CAVITY-NASAL FOSSE (FIG. XVIII).

The part of the human body wherein nature has placed the olfactory nerves (nerves of smell), is called the "nose." We distinguish the outer from the inner nose. Our attention is here called only to the inner nose, the nasal cavity. This is lined with mucous

membrane (within which the nerves of smell are distributed), and is intended not only for the sense of smell, but also quite especially for respiration. It is divided by a cartilaginous, vertical partition into two parts; its floor is, as already stated, formed by the hard-palate. The external orifices are called "nostrils;" the internal ones are the nares (choana). The latter communicate with the pharynx, and by means of this with the oral cavity, the larynx and the windpipe.

Fig. XVIII.-REPRESENTATION OF SECTION THROUGH HEAD AND NECK. A, the naso-pharynx; B, the oro-pharynx; C, the laryngo-pharynx; 4 is the superior and 5 the inferior turbinated process of the ethmoid bone; 6, the turbinated bone; 7, the hard and 8 the soft-palate; 9, the uvula; 10, anterior palatine arch; 11, lower jaw-bone; 12, tonsil; 13, orifice of the eustachian tube; 14, Rosenmueller's fossa; 15, tongue; 16, hyoid-bone; 17, posterior palatine arch; 18, vallecula; 19, epiglottis; 20, thyroid cartilage; 21, ventricular fold; 22, vocal cord; 23, arytenoid cartilage; 24, cuneiform cartilage; 25, cricoid cartilage; 26, anterior muscle; 27, supra-arytenoid cartilage; 28, lateral muscle; 29, thyroid body; 30, windpipe; 31, food pipe.

The air-capacity of the nasal fossæ exerts a great influence upon singing and speaking; less in expiration than in inspiration.