DIGESTION. 



157 



and posterior, formed respectively by the palato-glossei and palato-pharyngei 

 muscles. The superior laryngeal aperture is placed just beneath the base 

 of the tongue. It is triangular in shape, wide in front, narrow behind, and 

 directed downward and backward. It is bounded above by a thin plate of 

 cartilage, the epiglottis, placed just behind the tongue and so arranged that 

 it can easily be depressed and elevated. 



3 'The esophagus, the continuation of the deglutitory canal, extends down- 

 ward from the lower border of the cricoid cartilage for a distance of from 



FIG. 68. VERTICAL SECTION OF THE NASAL FOSSA AND MOUTH, i. Left nares. 2. Lateral 

 cartilage of the nose. 3. Portion of the internal alar cartilage forming the skeleton of the lower 

 part. 4. Superior meatus. 5. Middle meatus. 6. Inferior meatus. 7. Sphenoidal sinuses. 

 8. External boundary of the posterior nares. 9. Internal elliptical opening of the Eustachian 

 tube. 10. Soft palate, n. Vestibule of the mouth. 12. Vault of palate. 13. Genioglossus 

 muscle. 14. Geniohyoid muscle. 15. Cut margin of the mylohyoid muscle. 16. Anterior 

 pillar of the palate (anterior half-arch), presenting a triangular figure with the base inferiorly, 

 covering partly the tonsil. 17. Posterior pillar (posterior half -arch) of the palate. 18. Tonsil. 

 19. Follicular (mucous) glands at the base of the tongue. 20. Cavity of the larynx. 2 1. Ventricle 

 of the larynx. 22. Epiglottitis. 23. Cut os hyoides. 24. Cut thyroid cartilage. 25. Thyrohyoid 

 membrane. 26. Section of posterior portion of the cricoid cartilage. 27. Section of the anterior 

 portion of the same cartilage. 28. Crico- thyroid membrane. (Sappey.) 



22 to 25 centimeters, to a point opposite the ninth thoracic vertebra, where 

 it expands into the stomach. Its walls are composed of an internal or 

 mucous and an external or muscle coat, united by areolar tissue. The 

 muscle coat consists of an external layer of longitudinal fibers arranged in 

 three bands and of an internal layer composed of fibers arranged circularly 

 in the upper part and obliquely in the lower part of the esophagus. In the 

 upper third the fibers are striated; in the middle third they are a mixture of 

 both striated and non-striated; in the lower third they are entirely non- 

 striated. 



The muscle fibers surrounding the esophago-gastric orifice are arranged 

 in the form of and play the part of a sphincter muscle, and for this reason 



