to exert considerable pressure with impunity, and laxity enough that the lower jaw may execute horizontal movements. The action of the levator muscles is the most extensive; but the lateral or grinding motion is practicable to the necessary extent; and the muscles of both kinds have a medium degree of developement. The teeth, likewise, partake of the characteristics of those of the carnivorous and herbivorous animals;-twelve--the canine teeth and lesser molares--corresponding to those of the carnivorous; and twenty-the incisors and larger molares-to those of the herbivorous.

The tongue must be regarded as an organ of mastication. It rests horizontally on the floor of the mouth; is free above, anteriorly; and, to a certain extent, beneath and at the sides. Behind, it is united to the epiglottis by three folds of the mucous membrane of the mouth; and is supported at its base by the os hyoides, with which it participates in its movements. The tongue, as the organ of taste and articulation, is described elsewhere. We have only, therefore, to describe the os hyoides and its attachment to that bone. The hyoid bone has, as its name imports, the shape of the Greek letter v, the convex part being before. It is situate between the tongue and larynx and is divided into body or central part; and into branches, one extremity of which is united to the body by an intermediate cartilage, that admits of slight motion; whilst the other is free, and is called greater cornu. Above the point, at which the branch is articulated with the body, is an apophysis or process, called lesser cornu. The os hyoides is united to the neighbouring parts by fibrous organs, and muscles. The former are;-above, the stylo-hyoid ligament, which extends from the lesser cornu of the bone to the styloid process of the temporal bone; below, a fibrous membrane, called thyro-hyoid, passing between the body of the bone and the thyroid cartilage; and two ligaments, extending from the greater cornu of the hyoid bone to the thyroid cartilage, called thyro-hyoid. Of the muscles; some are above the hyoid bone, and raise it;-viz., the genio- and mylo-hyoideus, already referred to; the stylo-hyoid, and some fibres of the middle constrictor of the pharynx. Others are below, and depress it. They are the sterno-thyro-hyoideus, omo-hyoideus and sterno-thyroideus. The base of the tongue is attached to the body of the bone by a ligamentous tissue, and by the fibres of the hyoglossus muscle.

Among the collateral organs of mastication are those which secrete the saliva, and the various fluids which are poured out into the mouth, -constituting together what has been termed the apparatus of insalivation. These fluids proceed from different sources. The mucous membrane of the mouth, like other mucous membranes, exhales a serous or albuminous fluid, besides a mucous fluid secreted by the numerous follicles contained in its substance. Four glands likewise exist on each side, destined to secrete the saliva, which is poured into the mouth by distinct excretory ducts. They are the parotid, submaxillary, sublingual, and intra-lingual or lingual. The first is situate between the ear and the jaw; and its excretory duct opens into the mouth opposite the second small molaris of the upper jaw. By pressing upon this part of the cheek, the saliva can be made to issue into the mouth, in perceptibly increased quantity. The submaxillary

gland is situate beneath the base of the jaw; and its excretory duct

Fig. 5.

1. Parotid gland in situ, extending from the zygoma above, to the angle of the jaw below. 2. Duct of Steno. 3. Submaxillary gland. 4. Its duct. 5. Sublingual gland.

opens into the mouth, at the side of the frænum linguæ. The sublingual gland is situate under the tongue, and its excretory ducts open at the sides of that organ, and the intralingual or lingual is seated at the inferior surface of the tongue, where the mucous membrane forms a fringed fold. The saliva, as met with, is a compound of every secretion poured into the mouth; and it is this fluid which has been chiefly sub

jected to analysis. The secretion of the saliva, and its various properties, will be considered, however, hereafter.

The two apertures of the mouth are the labial and pharyngeal. The former, as its name imports, is formed by the lips, which consist externally of a layer of skin; are lined internally by a mucous membrane; and, in their substance, contain numerous muscles, elsewhere. described under the head of Gestures. These muscles may be separated into constrictors and dilators; the orbicularis oris being the only one of the first class, and the antagonist to the others, which are eight in number, on each side-levator labii superioris alæque nasi, levator labii superioris proprius, levator anguli oris, zygomaticus major, zygomaticus minor, buccinator, triangularis, and quadratus menti. To the last two muscles are added some fibres of the platysma myoides.

The pharyngeal opening is smaller than the labial, and of a quadrilateral shape. It is bounded above by the velum palati or pendulous veil of the palate; below, by the base of the tongue; and laterally, by two muscles, which form the pillars of the fauces. The pendulous veil is a musculo-membranous extension, constituting a kind of valve, attached to the posterior margin of the bony palate, by which all communication between the mouth and pharynx, or between the pharynx and nose can be prevented. To produce the first of these effects, it becomes vertical; to produce the latter, horizontal. At its inferior and free margin, it has a nipple-like shape, and bears the name of uvula. It is composed of two mucous membranes, and of muscles. One of the membranes,-that forming its anterior surface,-is a prolongation of the membrane lining the mouth, and contains numerous follicles; the other, forming its posterior surface, is an extension of the mucous membrane lining the nose, and is redder, and less provided with follicles than the other. The muscles that constitute the

body of the velum palati are -the circumflexus palati or spheno-salpingo-staphylinus of Chaussier; the levator palati or petro-salpingo-staphylinus; and the azygos uvula or palato-staphylinus. The velum is moved by eight muscles. The two internal pterygoids raise it; the two external pterygoids stretch it transversely; the two palatopharyngei or pharyngo-staphylini, and the two constrictores isthmi faucium or glosso-staphy lini carry it downwards. The

Angles and turning off the Lips.

1. Upper lip, turned up. 2. Its frænum. 3. Lower lip, turned down. 4. Its frænum. 5. Internal surface

last four muscles form the pil- Cavity of the Mouth, as shown by dividing the lars of the fauces;--the first two the posterior pillars; and the last two the anterior; between which are situate the tonsil glands or amygdala, which are composed of a congeries of

Fig. 7.

of cheeks. 6. Opening of duct of Steno. 7. Roof of

mouth. 8. Anterior portion of lateral half arches. 9.
Posterior portion of lateral half arches. 10. Velum

pendulum palati. 11. Tonsils. 12. Tongue.
mucous follicles.

a

b

Pharynx seen from behind.

1. A section carried transversely through base of skull. 2, 2. Walls of pharynx drawn to each side. 3, 3. Posterior nares, separated by vomer. 4. Extremity of Eustachian tube of one side. 5. Soft palate. 6. Posterior pillar of soft palate. 7. Its anterior pillar; the tonsil seen situate in the niche between the two pillars. 8. Root of tongue, partly concealed by uvula. 9. Epiglottis overhanging (10) opening of glottis. 11. Posterior part of larynx. 12. Opening into œsophagus. 13. External surface of esophagus. 14. Trachea.

2. The pharynx and oesophagus constitute a muscular canal, which forms the medium of communication between the mouth and stomach, and conveys the food from the former of these cavities to the latter. The pharynx has the shape of an irregular funnel,--the larger opening of the funnel looking towards the mouth and nose; the under and smaller end terminating in the oesophagus. Into its upper part, the nasal fossa, Eustachian tubes, mouth, and larynx open. It is inservient to useful purposes in the production of voice, respiration, audition, and digestion; and extends from the basilary process of the occipital bone, to which it is attached, as far as the middle part of the neck. Its trans. verse dimensions are determined by the os hyoides, larynx, and pterygo

1, 1. The vertical section of the head. 2. Points to the

spinal canal. 3. Section of the hard palate. 4. Inferior

spongy bone. 5. Middle spongy bone. 6. Orifice of the right nostril. 7. Section of the inferior maxilla. 8. Sec

tion of the os hyoides. 9. Section of the epiglottis. 10. Section of the cricoid cartilage. 11. The trachea, covered by its lining membrane. 12. Section of sternum. 13. In

side of the upper portion of the thorax. 14. Genio-hyoglossus muscle. 15. Its origin. 16, 17. The fan-like ex

pansion of the fibres of this muscle. 18. Superficialis hyoidens musele. 21. Mylo-hyoideus muscle. 22. Andes. 21. Levator menti. 25. Orbicularis oris. 26. Orifice pterygoid. 29. Section of velum pendulum palati, and azygos uvulæ muscle. 30. Stylo-pharyngeus. 31. Con medins. 33. Insertion of stylo-pharyngeus. 34. Consophagus. 38. Thyreo-arytenoid muscle and ligaments,

linguæ muscle. 19. Verticalis linguæ muscle. 20. Genio

terior belly of digastricus. 23. Section of platysma myoiof Eustachian tube. 27. Levator palati. 28. Internal

strictor pharyngis superior. 32. Constrictor pharyngis strictor pharyngis inferior. 35, 36, 37. Muscular coat of

and above is the ventricle of Galen. 39. Section of arytenoid cartilage. 40. Border of sterno-hyoideus.

maxillary apparatus, to which it is attached. It is lined by a mucous membrane, less red than that which lines the mouth, but more so than that of the oesophagus, and the rest of the digestive tube; and it is remarkable for the developement of its veins, which form a very distinct network. Around this is the muscular layer, the circular fibres of which are often divided into three muscles-superior, middle, and inferior constrictors. The longitudinal fibres form part of the stylo-pharyngei and palato-pharyngei muscles. The pharynx is raised by the action of the last two muscles, as well as by all those that are situate between the lower jaw and os hyoides, which cannot raise the latter without, at the same time, raising the larynx and pharynx. These muscles are: -mylo-hyoideus, genio-hyoideus, and the anterior belly of the digastricus.

The oesophagus is a continuation of the pharynx; and extends to the stomach, where it terminates. Its shape is cylindrical, and it is connected with the surrounding parts by loose and extensible areolar tissue, which yields readily to its movements. On entering the abdomen, it passes between

the pillars of the diaphragm, with which it is intimately united. The

mucous membrane lining it is pale, thin, and smooth; forming longitudinal folds, well adapted for favouring the dilatation of the canal. Above, it is confounded with that of the pharynx; but below, it forms several digitations, terminated by a fringed extremity, which is free in the cavity of the stomach. It is well supplied with mucous follicles. The muscular coat is thick; its texture is denser than that of the pharynx,--and cannot, like it, be separated into distinct muscles, but consists of circular and longitudinal fibres, the former of which are more internal, and very numerous, the latter external and less nume

rous.

3. The stomach is situate in the cavity of the abdomen, and is the most dilated portion of the digestive tube. It occupies the epigastric region, and a part of the left hypochondre. Its shape has been compared, not inappropriately, to that of the bag of a bag-pipe. It is capable of holding, in the adult male, when moderately distended, about three pints. The left half of the organ has always much greater

A, A. Anterior surface. B. Enlargement at lower part. D. Cardiac orifice. E. Commencement of duodenum. F and C. Coronary vessels. H. Omentum.

dimensions than the right. The former has been called the splenic portion, because it rests upon the spleen; the latter the pyloric portion, because it corresponds to the pylorus. The inferior border of the stomach, which is convex, is termed the great curvature or arch; the VOL. I.-6