180 ANATOMY OF VERTEBRATES. 



CHAPTER XVIIL 



ABSORBENT SYSTEM OF BIRDS. 



§ 151. The absorbents of Birds, as of Reptiles, differ from those 

 of Mammals in having fewer valves, which are also less perfect, 

 being so loose as frequently to permit for a certain extent a 

 retrograde passage of the injected fluid. The lacteals, lymphatics, 

 and thoracic ducts have very thin parietes, so as easily to be 

 ruptured : they are composed of two tunics, of which the internal 

 is the weakest. 



The lymph resembles that of Mammals, but the chyle differs 

 essentially in its transparency and want of colour. The lacteals 

 have, however, been observed to contain an opaque white fluid in 

 a Woodpecker that had been killed after swallomng a quantity 

 of ants. 



With respect to the disposition of the absorbents, 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 few in Birds ; the most 

 constant and conspicuous are those at the anterior part of the chest 

 or the root of the neck. Small ones have been seen in the axilla 

 and groin of sea-birds {Aptenodytes). In other parts of the body 

 the absorbent glands are replaced by plexuses of lymphatic vessels 

 surrounding the principal bloodvessels. 



The absorbents of Birds terminate principally by two thoracic 

 ducts, one on either side, which enter the right and left jugular 

 veins by several orifices ; the plexuses of the posterior part of the 

 body communicate mth the contiguous sacral and renal veins. 



The lymphatics of the foot unite to form the vessels which are 

 found running along the sides of each toe, fig. 89, i. In the 

 Palmipedes 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, 

 .'^, at the anterior part of the digitometatarsal joint, from which 

 three or four lymphatics are continued. The anterior and in- 



