428 THE DIGESTIVE APPARATUS IN MAMMALIA. 



colon, through the medium of a thick layer of cellular tissue. The anterior 

 border, concave and undulating, is in contact with the duodenum and the left 

 extremity of the stomach. The posterior is very convex, especially to the 

 right, and near its middle presents a notch for the reception of the portal 

 vein before its entrance into the ring. The right extremity (or head), the 

 thinnest, adheres to the duodenum, and shows the excretory ducts of the 

 gland. The left is carried towards the base of the spleen, in passing 

 between the left extremity of the stomach and the kidney of the same 

 side. 



Structure. It resembles the salivary glands, except in its epithelium. 

 This, instead of being simple polygonal cells lining the thin, structureless 

 membrane of the ultimate follicles, is very granular, and fills these cavities. 

 The gland receives its blood by the hepatic and great mesenteric arteries ; 

 the nerves come from the solar plexus. 



Excretory apparatus The pancreas has two excretory ducts : a principal, 

 described by Wirsung, whose name it bears, and an accessory. The duct of 

 Wirsung, lodged in the substance of the gland, but nearer the superior than 

 the inferior face, at first comprises two or three thick branches, which soon 

 unite to form a single trunk that emerges from the pancreas by the left 

 extremity of the organ. Larger than the ductus choledochus, it opens, as 

 already stated, at the same part of the duodenal surface. The accessory 

 duct (ductus pancreaticus minor) is much smaller ; it leaves the principal 

 trunk, receives some branches in its passage, and opens alone into the small 

 intestine, directly opposite the duct of Wirsung. 



The ductus choledochus and the duct of Wirsung do not pass directly 

 through the wall of the intestine, but obliquely, like the entrance of the 

 ureters into the bladder. They open in the middle of a circular valve the 

 ampulla of Vater. This ampulla is limited by a thick primary mucous 

 fold, and within this is a second, thinner, beneath which the ductus chole- 

 dochus opens ; at the bottom of the space circumscribed by this second fold, 

 beneath a free mucous lip, is seen the duct of Wirsung. 



FUNCTIONS. From the researches of Bernard, it appears established that 

 the fluid secreted by the pancreas emulsifies fatty matters and renders them 

 absorbable. 



3. The Spleen. 



The spleen differs from glands not only in the absence of an excretory 

 duct, but also in the other details of its organisation. It has been consi- 

 dered as a vascular gland, whose uses are not yet determined in a precise 

 manner. 



Situation. It is situated in the diaphragmatic region, close to the left 

 hypochondriac, and appears as if suspended in the sublumbar region, as well 

 as at the great curvature of the stomach. 



Form Direction Relations. The spleen is falciform, and directed 

 obliquely downwards and backwards. It has two faces, two borders, and a 

 point. 



The external face is in relation with the muscular portion of the 

 diaphragm, and is moulded to it. The internal, slightly concave, touches 

 the large colon ; it has sometimes a small lobule, or offers traces of lobula- 

 tion. The posterior border is convex, thin and sharp. The anterior, thicker, 

 concave, and bevelled at the expense of the internal face, is channeled by a 

 slight longitudinal fissure which lodges the splenic vessels and nerves ; it 



