302 INTERNAL ANATOMY OF HORSE. 



The thyroid is a gland which is found close to and 

 behind the larynx, beside the two first rings of the trachea. 

 This gland consists of two oval lobes of a reddish - brown 

 colour, united by the so-called "isthmus." It is more im- 

 portant in the young and foetus than in the adult, and is 

 especially developed in Euminants and Camivora. What its 

 functions are we do not know : some say it is to destroy the 

 mucin in the body, others that it is a gland connected with the 

 brain. Its excision does not materially affect the health of the 

 animal. 



The thymus is another ductless gland found in the foetus 

 only, resembling the thyroid, white and lobulated in form, and 

 partly situated in and partly out of the chest. 



Closely connected with the sub-lumbar region and the great 

 curvature of the stomach is a large vascular ductless gland, the 

 spleen. The spleen in the horse is falciform in shape, violet- 

 blue to red in colour, soft and elastic in texture. This gland is 

 really a floating gland, but is lightly attached by the great 

 omental peritoneum and by a suspensory ligament. It is an 

 organ that varies much in size, even in the same animal, often 

 becoming abnormally large. In the horse it weighs 32 ounces. 

 It is weU supplied with blood-vessels, and is almost solid. 

 Curious pale patches are found in the pulp that constitutes 

 the majority of the organ, called Malpighian corpuscles, de- 

 veloped in the course of the small splenic arteries. It is partly 

 employed in manufacturing red blood -corpuscles and in de- 

 stroying the same. Some physiologists look upon it as a 

 swelling or pouch of the portal vein. 



The peritoneum (fig. 158). — The organs and parts of the ali- 

 mentary canal are partly supported by a thin membrane, which 

 may be double owing to folding, called the peritoneum. This 

 serous membrane lines the walls of the abdominal cavity, and 

 from thence passes to and around the visceral parts. There are 

 then two kinds of peritoneum — the parietal (Pp), which is 

 applied to the body wall, and the visceral ( Pr), which supports 



