254 ANATOMY OF THE DOMESTIC FOWL 



the dorsal side of the proventriculus on the left side of the gizzard, 

 passes along the hilus of the spleen, and takes up several splenic 

 veins. 



The vena portalis dextra (Fig. 64, No. 40; Fig. 71, No. 4) receives 

 a vein near the base of the gall-bladder. This branch enters the 

 right lobe of the liver and unites with the vena portalis sinistra. 



The vena portalis sinistra (Fig. 71, No. 5) enters the left lobe of 

 the liver and there forms a sinus. It receives vessels which come 

 from the muscles of the gizzard, the inferior vena proventricularis, 

 and from the pro ventricular wall. 



The vena portalis propria receives small veins which come out of 

 the walls of the abdominal air-sacs and from the fat of the abdominal 

 walls. 



The vena umbilicalis originates in the umbilical region and empties 

 into the vena hepatica magna sinistra at a point where it comes out 

 of the liver (Fig. 70, No. 29). This is the remains of an embryonal 

 vein which collected all the blood of the yolk sac, passed on the left 

 side of the large intestine to the body, took up the vena mesenterica 

 and ended as the vena umphalo-mesenterica. 



THE LYMPHATIC SYSTEM 



The peculiarity of the lymph vessels is that they are associated 

 with organs in which lymph cells are formed. 



The lymphatic system consists of the lymph vessels and the cell- 

 forming organs. In some instances the cell-producing organs are 

 lymph follicles and in others lymph glands. For the most part the 

 glands are replaced by plexuses which in many places surround the 

 blood-vessels. 



The lymph of birds is similar to that of mammals. The larger 

 lymph vessels are similar to the veins, although the walls are always 

 thinner. Its tunica intima is rich in elastic fibers and has a layer 

 of endothelial cells on the inner side. The tunica media is formed 

 of rings of smooth muscle fibers. The adventitia is composed of 

 loose connective tissue. 



The lymph vessels frequently form plexuses. The large lymph 

 trunks follow the course of the larger blood-vessels, and frequently 

 surround the arteries. All the lymph vessels of the body, exclusive 

 of the lymph of the caudal region, form into a large trunk which 

 originates on both sides of the celiaca communis and passes upward 



