328 



AVES. 



The species in which the absorbent system 

 has been investigated are the Buzzard, Wood- 

 pecker, Turkey, Common Fowl, Bittern, He- 

 ron, Stork, Duck, Swan, Wild and Tame 

 Goose, but especially in the latter. 



The absorbents of Birds differ from those 

 of Mammals in having fewer valves, which 

 are also less perfect, being so loose as fre- 

 quently to permit for a certain extent a retro- 

 grade passage of the injected fluid. The lacteals, 

 lymphatics, and thoracic ducts have very thin 

 parietes, so as easily to be ruptured, but they 

 are composed, as in Mammals, of two tunics, 

 of which the internal is the weakest. 



The lymph resembles that of Mammals, 

 but the chyle differs essentially in its trans- 

 parency and want of colour. The lacteals 

 have, however, been observed to contain an 

 opake white fluid in a Woodpecker that had 

 been killed after swallowing a quantity of ants. 



With respect to the disposition of the ab- 

 sorbents, they do not form in Birds two strata, 

 as in Mammals ; at least those only have been 

 observed which correspond to the deep-seated 

 absorbents which accompany the large vessels. 



The lymphatic glands or ganglions are also 

 much less numerous in Birds than Mammals, 

 being in the former generally restricted in their 

 position to the anterior part of the chest or the 

 root of the neck. In the Penguin, however, a 

 femoral and two axillary absorbent glands have 

 recently been described.* They have the same 

 structure as in Man, but are softer. In other parts 

 of the body the absorbent glands are replaced 

 by plexuses of lymphatic vessels surrounding 

 the principal bloodvessels. It frequently hap- 

 pens, as in Mammalia, that two large absor- 

 bents form by their union a trunk, which is 

 of smaller diameter than either of the vessels 

 composing it. 



The absorbents of Birds terminate principally 

 by two thoracic ducts, one on either side, which 

 enter the jugular veins by several orifices. But 

 besides these communications, Tiedemann, 

 Fohman, Lauth, and Lippi state that the lym- 

 phatic plexuses of the posterior part of the 

 body communicate with the contiguous sacral 

 and renal veins. And Lauth describes several 

 intercommunications in other parts of the body; 

 these, however, are denied by Panizza, whose 

 careful and elaborate researches seem to prove 

 that the passage of the lymph into the venous 

 system takes place in Birds only in two places 

 in the pelvic region in addition to those by the 

 two thoracic ducts in the neck. 



The lymphatics of the foot unite to form 

 the vessels which are found running along the 

 sides of each toe (1, \,fig. 166). In the Pal- 

 mipedes there are anastomosing branches which 

 pass from the lateral vessel, of one toe to that 

 of the adjoining toe, forming arches in the 

 uniting web (2). These branches form a small 

 plexus (3) at the anterior part of the digito- 

 metatarsal joint, from which three or four 

 lymphatics are continued. The anterior and 

 internal branches (4) accompany the blood- 

 vessels, and form a network around them ; 

 the posterior and external branches (5) receive 



* Reid, iu Proceedings of Zool. Soc. Sept. 1835. 



Fig. 166. 



Absorbents of a Goose.* 



the lymphatics of the sole of the foot, then 

 ascend along the metatarsus, and form at its 

 proximal articulation a, close network (6); all 

 the vessels then ascend the tibia, forming a 

 plexus (7) around it as far as the middle of the 

 leg; then they unite into two branches, of 

 which the smaller passes along the anterior 

 part of the depression between the tibia and 

 fibula as far as the knee-joint, where it joins 

 the other branch which accompanies the blood- 

 vessels. The trunk formed by the union of 

 the two preceding branches accompanies the 

 femoral vessels, forming plexuses in its course 



* From Lauth 's Monograph, Annalesdes Sciences 

 Nat. t. iii. pis. 23 and 25. 



