Book VII. PHYSIOLOGY OF THE HORSE: 967 



' 6335. Cartilages are of three kinds, articular (1887.) which CoVer the ends of the bones by a thin layer, 

 enabling them to slide easily on one another; non-articular, or such as are placed between bones im. 

 moveably joined ; unattached, as those of the ears and larynx ; and temporary, as the ends of bones in very 

 young animals before their earthy deposit is completed. The general nature of cartilage is smooth, 

 white, solid, elastic, and hard. 



G33(i. The periosteum is a general uniting membrane to bones and their appendages (1882.) ; on the skull 

 it is called pericranium ; when it covers ligaments, peridesmium ; and perichondrium, when it invests 

 cartilage. Its uses appear to be to furnish vessels to the bones. It is little sensible, except under inflam, 

 mation, when it becomes highly so. 



6357- Medulla, or marrow, is a soft fatty substance deposited in the cavities of bones. 



6338. Ligatnents (1891.) are close, compact, fibrous substances, of immense strength in the horse, neces- 

 sary to bones as a connecting medium ; ligament is also a common membrane in every part of the body. 

 Ligament is considered inelastic ; there are, however, many exceptions, of which the cervical and meta- 

 carpal and metatarsal are instances. In some cases they are semicartilaginous. The suspensory ligaments 

 attach and suspend parts, as that of the thigh bone to its socket, &c, Capsular l.igarnents surround the 

 two opposed ends of jointed bones, and form a complete cavity. 



6339. The synovia or joint oil, being secreted from the inner surface of the capsular ligaments, fills up 

 this cavity, and affords a slippery medium, which enables the bones to slidereadily over each other. 



6340. Muscle is that part of the body of the horse which we term flesh, to distinguish it from skin, gristle, 

 bone, ligament, &c. Muscles appear composed of bundles of reddish fibres, the ultimate division of which 

 it is impossible to trace ; and as the motions of an animal are tery various, and as almost all motion is 

 Operated through the agency of the muscles; so the peculiar shape they take on is very varied. To the 

 generality of muscles, particularly to those ending in bones, is added a portion of a very different nature, 

 called tendon. 



6341. Tendons are insensible, inelastic, tough, fibrous substances, of a whitish colour: expanded into 

 tliin layers, they are called aponeuroses. The tendons are eminently useful to muscles, diminishing their 

 size without decreasing their strength. What would have become of the light elegant limb, had the large 

 muscular masses been continued to their terminations below^in equal dimensions ? Muscles are highly 

 vascular, as their colour testifies ; but the tendons are very little so, hence their powers of life are very 

 different : one can regenerate itself with ease, the other with extreme difficulty. The muscles also possess 

 a large share of nerves, and consequently of sensibility and irritability, to which properties the surprising 

 phenomena they exhibit must be attributed ; 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 dependent on their situation, and can change the fixed for the movable point, anAvice versa. 



6.342. 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.. Muscles are many of them covered by a cellular or membranous covering, caUed 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. Blood-vessels of the Horse. 



f?343. The arteries are long membranous canals, composed of three strata, which are called tunica; 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 haemorrhage 

 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 anastomosig, or by one branch uniting with another. They ter- 

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

 and the secretion appears under a totally diflTerent 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 

 from 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. 



6344. The aorta is the principal member of this system. Originating from the left ventricle of the heart 

 it soon divides into two branches, one of which, the anterior, or aorta ascendens {fig. 833. p), proceeds 

 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 ; and the posterior, or adrta descendens (o), which is distributed to the trunk and hinder 

 extremities. 



6345. The pulmonary artery is a trunk of five or six inches in length ; arising o>it of the anterior ven- 

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

 which it ramifies. 



6346. The veins are also membranous canals which begin where the arteries end, and return that blood 

 which has been distributed by their means. They have less solidity, and possess two tunics or coats only. 

 They usually accompany the arteries in their course, but are more numerous, being wisely divided 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. 



6347. The original venal trunks of the horse are ten in number ; the anterior cava, the posterior cava, 

 and eight pulmonary, to which may be added the vfena p6rtae. 



6348. The vena cava passes out of the heart by two trunks from separate parts of the right auricle. 

 The anterior, or cava ascendens (fig. 833. n), opposite to the first rib, divides into four principal trunks ; 

 two axillaries, and two jugulars, {fig. 833. r). The axillaries furnish the fore limbs under the names of the 

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

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

 hinder extremities. 



6349. The vena pirtcs is formed from the veins returning the blood from the viscera, which, uniting to 

 enter a sac of that viscus, are ramified through all parts of the liver, where the blood having undergone 

 some remarkable alterations is returned by the vt;na hepatica, and enters the heart by the posterior cava. 



6350. The blood is a homogeneous fluid, contained in the heart, arteries, and veins, and constantly 

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

 in the veins. The component parts of the blood are the cruor or coagulum; the coagulable lymph, < 

 fibrin, or gluten ; and the s^rum. The coagulum is composed of red globules, whose intensity of colour 

 is less in the horse than in man. A red colour is not necessary to the essential properties of blood, see- 

 ing the blood of some animals is white ; and even some parts of the horse's body are furnished with 

 colourless blood, as the transparent part of the eye, &c. Ihe coagulable lymph or fibrin (1941.) appears 

 the most essential part of the blood, and that from which all the parts are formed. The s^rum seems to 

 dilute the whole. The quantity contained in the body is uncertain : young animals possess more than 

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



