ABDOMINAL ORGANS OF DIGESTION IN THE HORSE. 33 



destined in the animal economy to originate motor influence, 

 which being conveyed through efferent nervous filaments to 

 the muscles having a share in deglutition, particularly to 

 those concerned in the elevation forwards of the hyoid bone, 

 that act occurs altogether independently of the will, or, to 

 speak technically, of volition. 



The act of deglutition in the horse is well illustrated by 

 attending to the corresponding act in man. As soon as a man 

 has collected the bolus on the tongue, and permitted it to pass 

 backwards towards the posterior part of that member, he loses 

 all control over it. If the finger be placed on the larynx, or 

 on the part termed Adam's apple, it is felt to rise forcibly at 

 the moment of swallowing ; and should the act fail to take 

 place with its usual regularity, a sense of sinking or of impend- 

 ing death arises, which technically is termed anxiety. 



Organs of Digestion in the Abdominal Cavity of the Horse. 

 The large trunk of the horse is divided, like that of other 

 similar animals, into thorax or chest, abdomen, and pelvis. 

 The chest, which is of great size, is bounded on the lower part 

 and sides by the breast-bone, and eighteen pairs of ribs, while 

 posteriorly it is separated from the abdominal cavity by the 

 great tendino-muscular partition termed the midriff or dia- 

 phragm. The abdominal cavity is bounded superiorly by the 

 lumbar vertebrae of the spine, and on the sides and below by 

 the large abdominal muscles extended between the ribs and 

 the margins of the pelvic bones. Owing to the concavity of 

 the posterior surface of the diaphragm, the abdominal cavity 

 extends considerably farther forward than the posterior mar- 

 gins of the ribs. The pelvis is the nearly straight, cylindrical 

 cavity formed at the posterior part of the trunk by the bones 

 of the pelvis. 



The whole of the alimentary canal is contained in the 

 abdominal cavity, with the exception of the gullet and the 



