The veins which originate about the region of the right auricle, empty directly into the right auricle of the heart through the valves of Thebesii. =The Alimentary Canal.=—The alimentary canal is a muscular membranous tube. It is about thirty feet in length, and extends from the mouth to the anus. It is lined throughout by a mucous membrane. The following outline will show the parts of the alimentary canal: Mouth Pharynx Oesophagus Stomach { Duodenum Small Intestines { Jejunum { Ileum { Caecum Large Intestines { Colon { Rectum The accessory organs to the alimentary canal are the following: Teeth, Salivary glands, Liver, Spleen, Pancreas. =The Mouth.=—The mouth is placed at the commencement of the alimentary canal. It is a nearly oval shaped cavity. In this cavity the mastication of the food and the insalivation of the food takes place. =The Teeth.=—The structure of the teeth has been considered under the head of tissues. =The Palate.=—The palate forms the roof of the mouth. It consists of two portions: The hard palate is in front and the soft palate is in the back. =The Salivary Glands.=—By the term salivary glands is usually understood the three chief glands on each side of the face. The parotid gland is placed near the ear. The submaxillary gland is placed below the jaw. The sublingual gland is placed below the tongue. These glands secrete the salival juices which are brought into the mouth by three small ducts, where it aids in the digestion of the food. The digestive action of the saliva is limited to the starchy foods. Its action is to change starches into sugars. [Illustration: FIG. 21—Passage into trachea and esophagus; Pharynx.] It also fulfills other important functions. By moistening the food it enables us to reduce the material to a consistency suitable for swallowing and for manipulation by the tongue and other muscles. The saliva also serves as a kind of lubricator that insures the smooth passage along oesophageal canal. =The Pharynx.=—The pharynx is that part of the alimentary canal, which is placed behind, and communicates with the nose, mouth and larynx. It is a muscular, membranous tube which extends from the back of the mouth and under surface of the skull to the level of the cricoid cartilage or to a point between the fifth and sixth cervical vertebrae. The pharynx is about four and one-half inches in length. Seven openings communicate with it, as follows: Two posterior nares, two eustachian tubes, mouth, larynx, esophagus. =The Esophagus.=—The esophagus or gullet is a muscular canal about nine or ten inches in length, extending from the pharynx to the stomach.