84 AMERICAN FARMER'S HORSE BOOK. 



extremity of the blade it extends across the top of the back, 

 where it rests upon the point of the vertebrae, and unites 

 with the corresponding tendon upon the opposite side. Thus 

 it hangs across the back like the pads of a saddle. 



Fistula, which will be described at length in Chapter YII, 

 is a swelling and ulceration of the serratus major, consequent 

 upon some external injury. Poll evil is a similar affection 

 of the smaller of these two singular tendons — or muscles, as 

 they are sometimes called — the seiraius minor, situated at 

 the top of the head, with which it connects the bones of the 

 neck. 



THE MEMBRANES. 



These form the thin, smooth coating that extends over all 

 the bones, separating them from the muscles, and that in- 

 closes the brain, lines all the cavities of the body, and covers 

 the bowels, kidneys, hearts, lungs, and the other organs of 

 similar location. They also line the mouth, the nostrils, the 

 throat, and trachea, and are found in all places throughout 

 the body where openings occur. 



They have received different names, according to their 

 locations and the parts which they invest. The prefix jperi, 

 signifying over or covering, is used in connection with 

 nearly all the more important of them, and, when thus em- 

 ployed, it designates the membrane which is over, or which 

 incloses, the particular organ or part. Thus the periosteum 

 invests the bones ; the pericranium lines the skull ; the peri- 

 cardium is the sack in which the heart is placed ; the peri- 

 toneum is the strong investing membrane of the external 

 surface of the bowels, and covers the walls of the entire 

 abdominal cavity. A notable exception to the usual nomen- 

 clature of the membranes is afforded by the pleura, which 

 envelops the lungs, and lines the cavity of the thorax, or 

 chest. Every farmer and butcher's boy is familiar with the 

 smooth, glossy appearance of the serous membrane through- 

 out the regions of the lungs and bowels, and elsewhere, in 

 the anatomy of the various domestic animals. 



