898 PRACTICE OF AGRICULTURE. Part III. 



buted ; while their extreme vascularity furnishes them with powers to keep the energies requisite for 

 these agencies. They contract and shorten at pleasure, acquire a power of acting dependant on their 

 situation, and can change the fixed for the movable point, and vice versa. 



5670. Muscles are voluntary and involuntary. The former are immediately under the influence of the 

 will, as those of the legs, eyes, mouth, &c. Involuntary muscles are such as are not under the guidance 

 of the will, and whose functions go on without control, as the heart, the respiratory and digestive mus- 

 cular organs. Voluntary muscles have usually antagonists, whereby the perpetual tendency to contraction 

 is counterbalanced : they are also usually covered by a cellular or membranous covering, called fascia, 

 and their tendons by another, but stronger investure, called theca or sheath. At the tendinous extremity 

 there is usually a capsule containing a quantity of lubricating mucus, the diseased increase of which 

 forms what is termed windgall. 



SuBSECT. 2. The Blood Vessels of the Horse. 



5671. The arteries are long membranous canals, composed of three strata, which are called tunicce or 

 coats, as, an external elastic, a middle muscular, and an internal cuticular. Each" of these coats is the 

 cause of some important phenomena, as well in disease as in health. The elastic power enables them to 

 admit a larger quantity of blood at one time than another, and thus they are turgid under inflammation : 

 by this also they can adapt themselves to a smaller quantity than usual ; otherwise a small hemorrhage 

 would^prove fatal. The muscular tunic appears to exist in much greater proportion in the horse than in 

 man, and this accounts for his greater tendency to inflammation, and also why inflammatory affections run 

 to their terminations so much sooner in the horse than in man. The arteries gradually decrease in their 

 diameter as they proceed from the heart. Our knowledge of the terminations of these vessels is very 

 confined ; we know they terminate by anastomosis, or by one branch uniting with another. They termi- 

 nate in veins, and they terminate on secreting surfaces, in which case their contents become changed, and 

 the secretion appears under a totally different form. Another common termination of the arteries is by 

 exhalant openings, by which sweat is produced. The use of the arteries is evidently to convey blood 

 fdfom the heart to different parts of the body, and according to the part the artery proceeds from, or pro- 

 ceeds to, so does it receive an appropriate name. 



5672. The aorta is the principal member of this system. Originating from the left ventricle of the hpart 

 it soon divides into two branches, one of vih\ch, the anterior, or aorta a$cendens{fig.61Sp),Y>Toceeds 

 forward to be divided into two principal divisions the carotids (q), by which the head is furnished, and 

 the axillaries, by which the fore limbs receive their blood, under the names of humeral, radial, and meta- 

 carpal arteries. The posterior, or aorta descendens (o), which is distributed to the trunk and hinder ex- 

 tremities, forms the other branch. 



5673. The pulmonary artery is a trunk of five or six inches in length ; arising out of the anterior ven- 

 tricle of the heart, and is continued by the side of the aorta. It soon divides and enters the lungs, 

 through which it ramifies. 



5674. ThQ veins are vessels^ which return the blood of the body which has been distri- 

 buted to it. They have less solidity, and possess two tunics or coats only. They usu- 

 ally accompany the arteries in their course, but are more numerous, being wisely (Hvidecl 

 into a superficial and a deep seated set, to avoid the dangerous effects of interruption. To 

 prevent the return of the blood they are furnished with valves also. 



5675. The original venal trunks of the horse are ten in number; as the anterior cava, 

 the posterior cava, and eight pulmonary, to which may be added the vena portae. 



5676. The vena cava passes out of the heart by two trunks from separate parts of the right auricle. 

 The anterior, or cava ascendens {fig. 618 n), opposite to the first rib, divides into four principal trunks ; two 

 axillaries, and two jugulars, {fig. 618 r). The axillaries furnish the fore limbs under the names of the hu- 

 meral, the ulnar, and the metacarpals. The jugulars {r) run up one on each side of the trachea to re- 

 turn the blood of the head. The posterior, or cava descendens (o), returns the blood from the body and 

 hinder extremities. 



5677. The vena ported is formed from the veins returning the blood from the viscera, which, uniting to en- 

 ter a sac of that viscus, are ramified through all parts of the liver, to have some remarkable operation 

 performed in their contained blood. Collected again after this operation, the blood is returned by the 

 vena hepatica, and carried into the posterior cava. 



5678. The blood is a homogenous fiuid, contained in the heart, arteries, and veins, and constantly cir- 

 culating through the whole body. It appears formed with the body ; is red in the arteries, and purple in 

 the veins. (5723.) The component parts of the blood are the cruor or coagulum; the coagulable 

 lymph, fibrin, or gluten ; and the serum. The coagulum is composed of red globules, whose intensity 

 of color is less in the horse than in man. A red color is not necessary to the essential properties of 

 blood, seeing the blood of some animals is white ; and even some parts of the horse's body are fur- 

 nished with colorless blood, as the transparent part of the eye, &c. The coagulable lymph or fibrin, 

 (1904.), appears the most essential part of the blood, and from which all the parts are formed. The se- 

 rum seems to dilute the whole. The quantity contained in the body is uncertain : young animals pos- 

 sess more than older, and hence bear bodily injuries better. It is less in quantity in fat than in lean 

 animals ; and in domesticated than in those which run wild. An animal will lose 1.15th before he dies. 

 A horse lost 44 pounds without apparent injury. Probably the quantity contained in the body may vary 

 according to circumstances: between 1.8th, and 1.10th of the whole mas's, is a fair medium. 



5679. JTie pulse. From the contraction of the heart and consequent dilatation of the arteries to receive 

 the blood, and pass it onward to all parts of the body, which is called the diastole; so a dilatation of the 

 heart and contraction of the arteries necessarily occurs, which is called the systole: and these two causes 

 operating alternately produce the phenomena of circulation. The momentary increase in capacity 

 in the diameter of the artery is called the pulse. As there is seldom disease present, without some 

 alteration in the circulation also, so the pulse is attended to as an indication of health or disease. The 

 circulation being carried on over the whole body, the pulse may be felt universally ; but some situations 

 are more favorable than others ; as the heart itself, the pasterns, at the root of the ear, &c. : but 

 the most convenient of all, is at the branch of the posterior jaw, where the maxillary artery may be rea- 

 dily detected, {fig. 618 t). The natural pulse in the horse is about 45 beats in a minute ; in the ox the 

 same ; m man 75; m the dog 90. When the pulse is much accelerated, the circulation is accelerated 

 also. If to its quickness, fulness of vessels and hardness are apparent, the circulation is ynorUdly hur- 

 ried, and inflammation general or partial is present. (5878.) 



SuBSECT. 3. The Absorbents of the Horse. 



* 5680. The absorbent system is a very extraordinary and a very important one, for if the blood builds 

 up and repairs parts, the absorbents pull down, remove, and take them away again. They are com- 

 posed of the lymphatics and lacteals. Both kinds, although thin and transparent, are strong, and appear 

 to have a contractile power: where very minute they are called capillaries. The lacteal absorbents are 

 situated in the mesentery and intestines, from whence they draw the chyle or nutritious fluid by which the 

 blood is nourished and augmented, by being carried forward from the mesentery into a tube called the 



