This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
* Descriptive and Illustrated Catalogue of the Physiological Series of Comparative Anatomy in the Museum of the Royal College of Surgeons of London, Parti, p. 100.
(2281). But whatever the degree of motion conferred upon the lower jaw, the muscles that act upon it are exactly comparable to those of the human subject. The masseter is strengthened in proportion to the hardness of the substances used for food; the temporal covers a greater or less extent of the cranium as the jaws are stronger or more feeble; and even the pterygoid muscles differ only in relative size and form from those of Man.
(2282). The digastric muscle, however, which is an important agent in depressing the lower maxilla, does not preserve the same arrangement in the lower quadrupeds that it presents in the human species. In Monkeys, indeed, it still exhibits two fleshy bellies, and a central tendon that traverses the stylo-hyoideus; but in general it is a single fleshy muscle, arising from the neighbourhood of the mastoid process, and inserted near the angle of the jaw.
(2283). The tongue, in nearly all the Mammifera, is composed of the same muscles as in Man; and their disposition is so similar as to render any detailed enumeration of them quite unnecessary. The only exceptions worthy of notice are found in the Ant-eater (Myrmecophaga) and in the Echidna, animals possessing tongues of remarkable length and slenderness, by means of which they secure their insect prey.
(2284). In both these animals the tongue suddenly becomes much contracted at the place where it begins to be free from the surrounding parts. It then appears to be made up of two very long and slender muscular cones, laid one upon the back of the other, their apices being at the end of the tongue *. Each of these cones consists of two muscles: one external, composed of a multitude of distinct fasciculi investing the internal muscle in a circular manner, and forming around it numerous little rings resembling the annelli of an earthworm. The internal muscle, on the contrary, is of great length; it arises from the middle and upper part of the sternum, runs forward along the neck, passes between two layers of the mylo-glossus, and afterwards becomes surrounded by the annular muscle; it is composed of distinct fasciculi, rolled upon themselves in an elongated spiral; the external fibres terminate at the first rings; those beneath attain the rings that succeed, and so on until the innermost fibres reach quite to the extremity of the tongue.
It is easy to perceive that, by its action, this muscle will shorten the tongue until it lies in a very small compass, or bend it in any direction; whilst the annular muscle will lengthen it, exactly in the same way as the body of a leech is extended or contracted.
* Cuvier, Lecjons d'Anat. Comp. iii. p. 264.
(2285). In the Ant-eater the annular muscle does not appear so distinctly double as it does in the Echidna; but it forms by itself almost all the substance of the tongue, which is thus capable of being elongated to a wonderful extent.
(2286). Regarding the tongue with reference to the sense of taste, the Mammalia may be looked upon as the only animals capable of receiving much enjoyment from this source, since in them alone the lingual mucous lining seems to be perfectly adapted to gustation. Even among these highly-endowed creatures, it is only in Man, and those Herbivorous orders that prepare their food in the mouth by a prolonged mastication, that the sense in question exhibits much delicacy of perception; for the Carnivorous quadrupeds, seeing that they tear to pieces and swallow their food in large morsels, can scarcely be supposed to pay much attention to its sapid qualities.
(2287). In the Cat tribe (Felidae), indeed, all the middle portion of the surface of the tongue is covered over with sharp, recurved, and horny spines, adapted, as it were, to file off remnants of soft flesh from the bones of their victims; and the gustatory papillae are elsewhere of small dimensions. The tongue of the Porcupine, likewise, is armed on each side near its extremity with broad, horny and sharp scales; but, with these exceptions, the mucous covering of the tongue, the various kinds of papillae upon different parts of its surface, and, moreover, the distribution of the nerves supplied to it, differ in no important circumstance from what is observed in the human organ of taste.
(2288). Importantly connected with the perfection of the sense of taste, and materially assisting in the mastication of food, is the salivary apparatus, which, throughout all the Mammalia, is made up of glands that offer the same general arrangement as in Man.
(2289). The parotids vary principally in their proportionate size; and their ducts always perforate the lining membrane of the mouth in the vicinity of the molar teeth.
(2290) The submaxillary and the sublingual glands are also very generally present; and, as in the human subject, the saliva that they furnish enters the mouth beneath the under surface of the tongue.
(2291). The mucous lining of the lips and cheeks is likewise studded with muciparous follicles, called, from their situation, buccal, molar, or labial glands; these likewise serve to lubricate the oral cavity.
(2292). In the Seals (Phocidae) there are no parotids, neither are these glands found in the Echidna liystrix, or in the Ant-eater (Myrme-cophaga); but in the last-named genus their place is supplied by two other secreting organs, of which Cuvier gives the following description*.
* Lecons d'Anat Comp. iii. p. 215.
One is in contact inferiorly with the upper edge of the masseter muscle, and fills up a great part of the space that represents the temporal, zygomatic, and orbital fossae, where it partially embraces the globe of the eye: the excretory duct derived from this gland opens into the mouth, behind the superior maxillary bone. The other, which is probably destined to furnish the viscid secretion that coats the worm-like tongue of this animal, is oval and flat, lying in front of the tendon of the masseter, behind the angle of the lips, and then running along the edge of the lower lip as far as its middle. Its canal opens externally in a groove at the commissure of the lips; and a white, thick and tenacious fluid may be pressed out from the cells of which the gland seems to be made up.