Читать книгу Delineations of the Ox Tribe - George Vasey - Страница 5

Table of Contents

Ruminantia is the term used by naturalists to designate those mammiferous quadrupeds which chew the cud; or, in other words, which swallow their food, in the first instance, with a very slight mastication, and afterwards regurgitate it, in order that it may undergo a second and more complete mastication: this second operation is called ruminating, or chewing the cud. The order of animals which possess this peculiarity, is divided into nine groups or genera, namely:—

Camels.

Llamas.

Musks.

Deer.

Giraffes.

Antelopes.

Goats.

Sheep.

Oxen.

The last named forms the subject of the following pages, and is called, in zoological language, the Genus Bos, in popular language, the Ox Tribe.

One of the most interesting occupations which the wide field of Zoology offers to the naturalist, is the investigation of those remarkable adaptations of organs to functions, and of these again to the necessities and well-being of the entire animal. Nor does it in the least diminish our interest in the investigation of individual adaptations, or our admiration on becoming acquainted with them, that we know, à priori, this universal truth, that all the constituents of every organised body, be that organisation what it may, are invariably adapted, in the most perfect manner, to each other, and to the whole.

It is by a knowledge of this exact harmony in the animal economy, that the comparative anatomist can determine, with almost unerring precision, the genus, or even species of an animal, by an examination of any important part of its organisation, as the teeth, stomach, bones, or extremities. In some cases, a single bone, or even the fragment of a bone, is sufficient to convey an idea of the entire animal to which it belonged.

In illustration of this:—if the viscera of an animal are so organised as only to be fitted for the digestion of recent flesh, we find that the jaws are so contracted as to fit them for devouring prey; the claws for seizing and tearing it to pieces; the teeth for cutting and dividing its flesh; the entire system of the limbs, or organs of motion, for pursuing and overtaking it; and the organs of sense for discovering it at a distance. Moreover, the brain of the animal is also endowed with instincts sufficient for concealing itself, and for laying plans to catch its necessary prey.

Again, we are well aware that all hoofed animals must necessarily be herbivorous, or vegetable feeders, because they are possessed of no means of seizing prey. It is also evident, having no other use for their fore-legs than to support their bodies, that they have no occasion for a shoulder so vigorously organised as that of carnivorous animals; owing to which they have no clavicles, and their shoulder-blades are proportionally narrow. Having also no occasion to turn their forearms, their radius is joined by ossification to the ulna, or is at least articulated by gynglymus with the humerus. Their food being entirely herbaceous, requires teeth with flat surfaces, on purpose to bruise the seeds and plants on which they feed. For this purpose, also, these surfaces require to be unequal, and are, consequently, composed of alternate perpendicular layers of enamel and softer bone. Teeth of this structure necessarily require horizontal motions to enable them to triturate, or grind down the herbaceous food; and accordingly the condyles of the jaw could not be formed into such confined joints as in the carnivorous animals, but must have a flattened form, correspondent to sockets in the temporal bones. The depressions, also, of the temporal bones, having smaller muscles to contain, are narrower and not so deep; and so on, throughout the whole organisation.

The digestive system of the ruminantia is more complicated in structure than that of any other class of animals; and, owing to this complexity, and the consequent difficulty of investigating it, its nature and functions have been less perfectly understood.

The stomach of the Manilla Buffalo, which will serve as an example of all the other species, is divided into four cavities or ventricles, which are usually (but improperly) considered as four distinct stomachs.

The following figure represents the form, relative size, and position of these four cavities when detached from the animal, and fully inflated.

a. First cavity, called the paunch. b. Second ditto, the honeycomb bag. c. Third ditto, the many-plies. d. Fourth ditto, the reed, or rennet. e. A portion of the œsophagus, showing its connection with the stomach. f. The pylorus, or opening into the intestines.

The interior of those cavities present some remarkable differences in point of structure, which, in the present work, can only be alluded to in a very general manner. For a particular account of the internal anatomy of these complicated organs, the reader is referred to the interesting work on 'Cattle,' by W. Youatt.

The paunch is lined with a thick membrane, presenting numerous prominent and hard papillæ. The inner surface of the second cavity is very artificially divided into angular cells, giving it somewhat the appearance of honeycomb, whence its name "honeycomb-bag." The lining membrane of the third cavity forms numerous deep folds, lying upon each other like the leaves of a book, and beset with small hard tubercles. These folds vary in breadth in a regular alternate order, a narrow fold being placed between each of the broader ones. The fourth cavity is lined with a velvety mucous membrane disposed in longitudinal folds. It is this part of the stomach that furnishes the gastric juice, and, consequently, it is in this cavity that the proper digestion of the food takes place; it is here, also, that the milk taken by the calf is coagulated. The reed or fourth cavity of the calf's stomach retains its power of coagulating milk even after it has been taken from the animal. We have a familiar instance of its operation in the formation of curds and whey.

The first and second cavities (a and b) are placed parallel (or on a level) with each other; and the œsophagus (e) opens, almost equally, into them both. On each side of the termination of the œsophagus there is a muscular ridge projecting, so that the two together form a sort of groove or channel, which opens almost equally into the second and third cavities (b and c).

[As there has not been, as far as I am aware, any appropriate name given to this very remarkable part of the stomach of ruminants, I here take the liberty of suggesting the term Gastro-duct, by which epithet this muscular channel will be designated in the following pages.]

View of Gastro-duct, after Flourens. a. A portion of the œsophagus cut open, showing the internal folds of the mucous membrane. b. The opening of the œsophagus into the paunch. c, c. The gastro-duct. d, d. Muscular fibres passing completely round the edge of the gastro-duct, and forming a sort of sphincter. e. The opening from the gastro-duct into the third cavity.

All these parts, namely, the œsophagus, the gastro-duct, and the first three cavities, not only communicate with each other, but they communicate by one common point, and that point is the gastro-duct. At the extremity of the third cavity, opposite to that at which the gastro-duct enters it, is an aperture which communicates immediately with the fourth cavity (d).

Such is a very brief description of the complicated stomach of the Ox Tribe. In what manner the food passes through this curious arrangement of cavities is a problem which has engaged the attention of naturalists from a very early period. A host of great men might be cited who have failed to solve it. The French physiologist, M. Flourens, by his recent experiments, has done more than any or all of his predecessors to give clearness and precision to this intricate subject.

The following is an abstract of the most important of his experiments:—

A sheep having been fed on fresh trefoil, was killed and opened immediately—that is, before the process of rumination had commenced. He (M. Flourens) found the greatest part of this herb (easily recognised by its leaves, which were still almost entire,) in the paunch; but he also found a certain portion (une partie notable) of those leaves (in the same unmasticated state) in the honeycomb. In the other two cavities, (the many-plies and the reed,) there was absolutely none.

M. Flourens repeated this experiment a great many times, with herbs of various kinds, and the result was constantly the same: from which it appears, that herbaceous food, on its first deglutition, enters into the honeycomb, as well as into the paunch; the proportion, however, being considerably greater into the paunch than into the honeycomb. It appears equally certain that, in the first swallowing, this kind of food only enters into the first two cavities, and never passes into the many-plies or the reed.

Having ascertained this fact with respect to herbs, he instituted a similar series of experiments, in which the animals were fed upon various kinds of grain—rye, barley, wheat, oats, &c. The animals were killed and examined, as in the former experiments, immediately after being fed. He found the greater part of the grain unmasticated (tout entier) in the paunch; but, as in the case of the herbs, he also found a certain portion, in the same unmasticated state, in the honeycomb. Neither the many-plies nor the reed contained a single grain. He repeated these experiments many times, and always with the same result.

He then tried the effect of carrots cut into pieces, from half an inch to an inch in length; and in order that the animals might not chew them, he passed them into the pharynx by means of a tube. In one of these sheep he found all the morsels in the paunch; but, in the other two, some of the morsels were in the honeycomb, and some in the paunch. In all the three cases, there was none either in the many-plies or in the reed.

He then proceeded to ascertain the effect of substances previously comminuted. He caused a certain quantity of carrots to be reduced to a kind of mash, with which he fed two sheep, and opened them immediately afterwards. He found the greatest part of this mash in the paunch and in the honeycomb; but he likewise found a certain portion in the many-plies and in the reed.

His next experiments were made upon plain fluids. It is the opinion of the generality of authors on this subject that fluids pass immediately and entirely, along the gastro-duct, into the third and fourth cavities. But, according to the experiments of M. Flourens, this is not the case. He found, by making artificial openings (anus artificiel) in the stomachs of various sheep, that, as the animals drank, the fluid came directly out at the opening, in whatever cavity it might have been made.

It is clear, then, that fluids pass, in part, into the first and second cavities, and, in part, into the third and fourth; and they pass as directly into the former as into the latter.

The following is the result of some experiments which M. Flourens made respecting the formation of the pellets.

In the first place, after the animal has swallowed a certain quantity of food the first time, successive pellets are formed of this food, which remount singly to the mouth; secondly, there is a particular apparatus, which forms these pellets; and, thirdly, this apparatus consists of the two closed apertures (ouvertures fermées) of the many-plies, and of the œsophagus. Thus, the first two cavities, in contracting, push the aliments which they contain between the edges of the gastro-duct; and the gastro-duct, contracting in its turn, draws together the two openings of the many-plies and œsophagus; and these two openings, closed at this moment of their action, seize a portion of the food, detach it, and form it into a pellet.

The chief utility of rumination, as applicable to all the animals in which it takes place, and the final purpose of this wonderfully-complicated function in the animal economy, are still imperfectly known; what has been already suggested on these points is quite unsatisfactory. Perrault and others supposed that it contributed to the security of those animals, which are at once voracious and timid, by showing the necessity of their remaining long employed in chewing in an open pasture; but the Indian buffalo ruminates, although it does not fly even from the lion; and the wild goat dwells in Alpine countries, which are inaccessible to beasts of prey.

Whatever may be our ignorance of the cause or the object of rumination, it is certain that the nature of the food has a considerable influence in increasing or diminishing the necessity for the performance of that function. Thus, dry food requires to be entirely subjected to a second mastication, before it can pass into the many-plies and reed; whilst a great portion of that which is moist and succulent passes readily into those cavities, on its first descent into the stomach.

It has already been shown by the illustration, (p. 4,) that the paunch is the largest of the four cavities; but this is not the case with the stomach of the young calf, which, while it continues to suck, does not ruminate; in this case the reed, which is the true digestive cavity, is actually larger than the other three taken together.

When the calf begins to feed upon solid food, then it begins to ruminate; and as the quantity of solid food is increased, so does the size of the paunch increase, until it attains its full dimensions. In this latter case, the paunch has become considerably larger than the other three cavities taken together.

A curious modification of an organ to adjust itself to the altered condition of the animal is beautifully shown in the instance now under consideration, the nature of which will be easily understood by a reference to the following diagrams, giving the exact relative proportions of the different cavities of the stomach to each other in the young calf and in the full-grown cow.