567. The roof of the mouth, called the palate, consists partly of bony and partly of membranous substance. The bony part of the palate forms an arch in the upper jaw, the position of which in the erect posture is horizontal: the membranous part of the palate consists of the mucous membrane of the mouth, which affords a covering to the bony part of the palate. [Illustration: Fig. CLII.—_View of the Mouth, showing particularly the Soft Palate, Tonsils, and Tongue._ 1. Anterior arch of the soft palate. 2. Posterior arch. 3. Tonsils or amygdalæ. 4. Uvula. 5. Communication between the mouth and pharynx. 6. The tongue. 7. Anterior or nervous papillæ. 8 and 9. The upper and lower turbinated bones dividing the nostrils into (10) chambers.] [Illustration: Fig. CLIII.—_A side view of the Mouth, Pharynx, Nose, &c._ 1. Mouth. 2. Tongue. 3. Section of the lower jaw. 4. Submaxillary gland. 5. Sublingual gland. 6. Hyoid bone. 7. Thyroid cartilage. 8. Thyroid gland. 9. Trachea. 10. Interior of the pharynx. 11. Section of the soft palate. 12. The esophagus. 13. The interior of the nose. 14. The two spongy bones dividing it into three chambers. 15. The posterior communication with the upper part of the pharynx.] [Illustration: Fig. CLIV.—_Posterior view of the Nose, Mouth, Larynx, and Pharynx laid open._ 1. Posterior openings of the nose, communicating with the upper part of the pharynx. 2. Posterior surface of the soft palate. 3. The uvula. 4. Back part of the mouth communicating with the pharynx. 5. The tonsils. 6. Back part or root of the tongue. 7. Posterior surface of the epiglottis. 8. The larynx. 9. The opening of the larynx into the pharynx. 10. Cut edges of the pharynx. 11. Esophagus, the continuation of the pharynx. 12. The Trachea, continuation of the larynx. 13. Muscles acting on the pharynx.] 568. From the posterior part of the bony arch of the palate is suspended, transversely, a moveable partition, called the soft palate (fig. CLII. 1 and 2), which is composed of muscular fibres enclosed in the mucous membranes of the mouth. No less than ten distinct muscles enter into the composition of the soft palate. These muscles are disposed in such a manner that they render the organ capable of descending and of applying itself against the tongue (fig. CLII. 6), so as completely to close the passage between the mouth and the pharynx (figs. CLII. 5, and CLIV. 1), and of ascending and carrying itself obliquely backwards towards the posterior wall of the pharynx, so as completely to close the passage between the pharynx and the nose (fig. CLIV. 2, 1); hence this moveable partition performs the office of a double valve, closing the passage from the mouth to the pharynx, and from the pharynx to the nose.