236 OUTLINES OP EQUINE ANATOMY. 



run ; from this tlie organ decreases in thickness towards 

 the greater or free curvature, around which the serous 

 membrane is reflected joining the layers on the surfaces ; 

 the curvatures meet at the apex. The special ca29s^^Ze oftlie 

 spleen consists mainly of yellow elastic tissue, whereby it is 

 endowed with great capacity of distension, for it is an 

 erectile organ. From this outer covering trabecules or 

 septa project inwards in all directions, thus dividing the 

 organ into spaces which contain a peculiar reddish matter, 

 spleen pulp, ai^tly compared to raspberry jam. On ex- 

 amination under the microscope this is found to consist 

 essentially of large cells, each containing one or more red 

 cells, in a more or less advanced state of disintegration, 

 for it is supposed that the spleen is the organ whereby 

 excess of red corpuscles in the blood is prevented. The 

 spaces between the trabeculse also contain vessels. The 

 arteries, derived from the splenic branch of the coeliac axis, 

 terminate in venous sinues, and are also remarkable for pre- 

 senting at various intervals, embedded in their fibro-areolar 

 coat, small bodies analogous in structure to the solitary 

 glands of the intestines. These are Malpighian corpuscles, 

 the use of which is not known, and which consist of aggre- 

 gations of cells embedded in a fibrous stroma. The veiiis of 

 the spleen commence from the venous sinuses, they have 

 few if any valves, and pour their contents into the vena 

 portse. The nerves of the spleen are derived from the 

 semilunar ganglion. The prerenal capsule is another organ 

 the use of which is undetermined. There is one on either 

 side of the body, situated between the kidney and the 

 spine, and presenting two surfaces. It derives its blood 

 by a special arterial branch, either from the posterior aorta 

 or from the renal arteiy. When cut into it presents an ex- 

 ternal dark, or cortical portion, the use of which is unknown ; 

 and a central lighter medullary part, supposed to be a nerve 

 centre. It is included among the ill-understood ductless 

 or vascular class of glands. 



Having removed the alimentary viscera from the belly 

 we are enabled to examine the structures situated in the 

 upper part of the cavity. On the central line we see im- 

 portant vessels and nerves. The posterior aorta, after 

 passing through hiatus aorticus of the diaphragm in 

 company with the thoracic duct and vena azygos, runs 

 backwards, inclined to the left side of the spine. In its 



