476 



THE ANATOMY OF THE HORSE 



glandular structure, though differing iu their miuute anatomy. The 

 alimentary canal consists throughout of three distinct layers : the external 

 serous coat {]>crito)ical), the middle or tmiscidar coat, and the internal 

 mucous coat, wliich are unitcil by cellular membrane, sometimes regarded 

 as forming two distinct additional coats. 



TuE PERITONEUM, like the pleura, is a serous membrane, forming a shut 

 sac, and arranged in such a manner that all the abdominal organs are 

 behind it, and two layers of it must be divided before reaching the interior 

 of ftuv of the organs from the lateral or inferior boundaries of the abdomen. 



FiQ. 76.— Sectional Pl.vn of the Iloi.b.. „ 



A. A. Largo intestines. 



B. B. B. Small intestines. 



C. C. C. reritoncum covering intestines. 



D. D. reritoncum lining the walls of tlio ab- 



domen. 



E. E. Folds connecting the large intestine 



with the iiarietal peritoneum, called 

 mesocolon. 



...N BEUl.VD THE STOMACH AND LlVEB. 



F. F. Folds connecting the small intestines 

 with the same, and called the mesen- 

 tery. 

 O. Abdominal muscles. 

 H. H. Ribs. 

 1. I. lAiinbar muscles. 

 J. J. Kiibieys embedded in fat. 



This will be better understood by examining the annexed plan, in which 

 the solid black part represents the interior of the peritoneal sac, a space 

 usually extremely small, but capable of being distended to a great extent 

 by a secretion of serum from the internal surface, as in abdominal drop.sy. 

 The white line indicates the whole continuous surface of the peritoneum 

 inclosing the black space, which is exaggerated, in order to render the plan 

 more distinct. It will thus be readily understood that unless the perito- 

 neum is detached from the upper walls of the abdomen, and its layers are 

 separated, as at E E, the viscera cannot be reached without di\ i<Hng it 

 twice ; first, as it lines the walls of the abdomen; and .secondly, as it closely 

 covers the organ which it is desired to open. In certain conditions it is 

 important to remember this, as for instance in distended states of the 

 colon, when it may be a question whether the bowel may be punctured 

 from the flank without wounding the peritoneum. It is a very delicate 

 and irritable membrane in the horse, and should never be interfered with if 

 it is possible to avoid it. Its secretion is a clear serum, merely sufficient 



