156 ANATOMY OF THE DOMESTIC FOWL 



They are distributed throughout the splenic pulp. Each splenic 

 corpuscle contains one or more small arteries. These extend near 

 the periphery of the corpuscle and more rarely in the center. 



The splenic artery passes in and the splenic veins out at the 

 hilum which is located on the concave, or attached, side of the 

 spleen. The splenic artery, upon entering the organ, at once 

 branches, the trabeculae forming a support for the vessels. 



After the arteries have entered the hilum, as stated above, they 

 divide into many branches which follow the septa of the connective 

 tissue. At first the arteries are accompanied by branches of the 

 splenic veins. Soon, however, the arteries leave the veins and the 

 septa, and penetrate the splenic pulp. In the splenic pulp the 

 adventitia of the smaller arteries assume the character of reticular 

 tissue, and become infiltrated with lymphoid cells. This infiltration 

 forms masses which are called the splenic corpuscles, or Malpighian 

 bodies. The terminal arteries break up into capillaries, which still 

 retain an adventitia, and empty into border spaces, or sinuses, 

 sometimes spoken of as ampullae. These sinuses in turn empty into 

 cavernous sinuses of the splenic pulp. From these are finally 

 formed the venules; and the collections of venules form the splenic 

 veins through which the blood gains exit from the spleen. 



The Abdominal and Pelvic Cavities. In birds the abdominal 

 cavity is divided into two smaller cavities by a fibrous septum. The 

 anterior cavity representing the abdominal contains the liver, and 

 the other representing the pelvic contains the gizzard, intestines and 

 oviduct. 



The Peritoneum and the Mesentery . The abdominal and pelvic 

 cavities are lined by the peritoneum. Like all serous membranes 

 this is composed of a parietal and a visceral portion, which together 

 form a complete sac, with the organs it covers situated on the outer 

 side. The peritoneum like other serous membranes consists of a 

 mesothelial and a submesothelial portion, the cells of the former 

 being arranged in a single layer. Since a serous membrane is so 

 arranged as to line a closed cavity, and at the same time to cover 

 its contents, it follows that the entire membrane must be a closed 

 sac, the mesothelial layer being on the inside; such a sac is called 

 a serous sac, or cavity. Synovial membranes are also regarded as 

 a variety of serous membranes. The fold, or layer, of the mem- 

 brane which lines the cavity is called the parietal, that which 

 covers the greater part of the organs contained therein is called the 



