Mouth. -- The mouth is separated from the nose by the hard and softpalate, and communicates. It is bounded in front by the lips, and itssides by the cheeks. The space between the lips and teeth is calledthe vestibule. The mouth is lined by a mucous membrane, which iscovered by numerous glands, some being mucous and somesalivary. The mouth contains a double row of teeth, thirty-two in theaggregate, performing the first process in digestion, the masticationof food.
Between the anterior and posteriorarches of each side is the tonsil gland.The tonsils are about the size of analmond, and consist of a collection oflarge mucous follicles.
Salivary Glands. -- The salivary glandsare of light pink color, and theirsecretion is of great service inmastication and digestion. There arethree in number -- the parotid,submaxillary, and sublingual. Theparotid is the largest; it lies on the sideof the face in front of the ear, andbeneath the skin. The submaxillary liesin a depression on the internal face ofthe lower jaw-bone. The sublingual isthe smallest of the three; it is situatedunder the tongue.
Pharynx. -- The pharynx is a muscularand membranous sac, communicatingwith the mouth, nose, oesophagus,larynx, and the tube (Eustachian)leading to the ear. Its length is aboutfive inches, although this varies byextension and contraction. Its uses arefor deglutition, respiration, andmodulation of the voice
Oesophagus. -- This is the canal thatconveys the food from the pharynx tothe stomach. Its length is about nine orten inches, and its diameter is notuniform, gradually increasing (as itdescends). Its upper portion is thenarrowest part of the alimentary canal;and hence foreign bodies which are toolarge to pass through the alimentarycanal are generally arrested in the neck.It never contains air. Deglutition isperformed by the contraction of thelongitudinal fibres of the oesophagus,which shorten the passage, and bycontraction of its circular fibressuccessively from above downward.
Tongue. -- The tongue is an oblong, flattened, muscular body, which varies insize and shape; it is the organ of taste, and also of importance in speech andmastication. Its posterior extremity or root is attached to a bone, called thehyoid, by yellow fibrous tissue. Its anterior extremity is called the tip; itsintervening portion its body. The mucous covering of the tongue is very thickupon its upper surface, and very thin upon its under surface. Upon its uppersurface are a number of projections, of various sizes and shapes, calledpapillae. The largest are eight or nine in number, called papillae maximae, andare situated at the posterior portion of the tongue, in two convergent lines.The smallest papillae are fine and pointed, and are found near the middle ofthe tongue, and are termed filiform. The tongue assists in the process ofdeglutition.
Palate. -- The palate separates the back portion of the nose fromthe mouth, and is divided into two parts. The hard palate, of abony base, covered by mucous membrane, which is continuouswith that of the mouth; the soft palate is the membranousseparation between the back portion of the mouth and nose. Fromthe middle the uvula projects, about three quarters of an inch inlength; from each side of the uvula there are two divergentcreswcdentic folds of mucous membrane, which are called lateralhalf-arches; the space between which constitutes the fauces.
Stomach. -- The stomach is a conoidal sac, somewhat bent or curved, andsituated below the breast-bone or in the epigastric region. The leftextremity is much the larger, and terminates in a rounded sac; at theupper portions of this extremity is the cardiac orifice where theoesophagus is continued into the stomach, immediately below thediaphragm. The right extremity is continuous with the intestines, and itsorifice is called the pyloric. The structure of the pylorus is much thickerthan that of any other portion. The stomach is held in its position by theoesophagus and the duodenum, as well as by reflexions of theperitoneum. The upper and lower curvatures of the stomach are called thegreater and lesser curvatures. Near the pyloric extremity of the stomach isa small dilatation called the antrum pylori. The dimensions of the stomachare variable, depending upon the mode of life. It has four coats; theperitoneal, muscular, cellular and mucous.
In the stomach the food receives theadmixture of the gastric juice, which isthe solvent agent of digestion. Thefluids taken into the stomach are for themost part absorbed from it; the solids,with the exception of the insolubleparts, are by the action of the gastricjuice reduced to a substance calledchyme, which in general is grayish,semi-fluid, homogeneous, with aslightly acid taste and smell. The chymeis then poured into the duodenumthrough the pyloric orifice for thesubsequent action of the intestines.
Intestines. -- The intestinal canal is fromthirty to thirty-five feet in length, and isdivided into large and small intestines.The small intestine is four-fifths of thelength of the whole canal, reaching fromthe pylorus to the large intestine; it iscylindrical, and about one inch indiameter; there is a gradual diminutionin calibre as it descends. Its coats arethe same as those of the stomach. Themucous coat is very vascular, and itsabsorbents are very numerous. Theglands are the crypts or follicles ofLieberkuhn, the glands of Peyer, thesolitary glands, and Brunners glands.
The small intestine is divided intoduodenum, jejunam, and ileum.The Duodenum commences at thepylorus, and is about twelve incheslong. The common duct formed by thejunction of the bile and gall ducts opensinto it about four or five inches from thepylorus. The Jejunum (from jejunus,empty) constitutes the upper two-fifthsof the small intestine, and the ileum theremaining three-fifths
The large intestine reaches from the ileum to the anus, and is one-fifthin length of the whole canal; it differs much from the small intestine,and has a sacculated appearance. It likewise has four coats. It isdivided into caecum, colon, and rectum.The Caecum is a cul-de-sac or blind sac, and the commencement ofthe large intestine, and hence often called the caput coli. At theinferior portion is a worm-like process called the appendixvermiformis. On the side of the caecum is the ileo-caecal valve, anelliptical opening whereby the small intestine empties into the large.The Colon is the largest portion of the large intestine; graduallydiminishes in diameter until it terminates in the sigmoid or S-likeflexure on the left side. It ascends on the right side, and forming anarch transversely, descends upon the left side. The Rectum is theterminating portion of the large intestine, and reaches from thesigmoid flexure to the anus. It is somewhat barrel-shaped, being larger in the middle than at either end.