LYMPHATIC SYSTEM. 617 



to appear like a mass of absorbents, where the finer in- 

 ternal vessels accompany the divisions of the veins through 

 its texture, and the larger exterior lymphatics form by 

 their confluence, a considerably superficial sinus. They 

 abound on the mucous and serous membranes and through- 

 out the adipose substance of this animal, they present 

 a regular arborescent appearance on the testicle, and are 

 comparatively rare on the liver, the gall-bladder and the oeso- 

 phagus. The distinct compact external intestinal layer of 

 absorbents, probably belongs to the lymphatic rather than 

 to the chyliferous system. In the crocodile and the green 

 lizard, Panizza found the lymphatics particularly abundant 

 and forming distinct layers around the cloaca and the termi- 

 nal portion of the intestine, the heart of the crocodile ap- 

 peared enveloped in a plexiform layer of these vessels, but 

 he could not inject those of the liver, the testicle, or the pe- 

 ricardium. In the turtle, the crural plexuses derived from the 

 lymphatics of the posterior extremities, together with the 

 renal, the rectal, the cloacal, and the sacral plexuses, unite 

 with the lymphatics of the peritoneum, the adipose substance 

 of the abdominal parietes, and part of the lungs, and the 

 great chyliferous trunks, to form the wide reticulate commen- 

 cement of the anastomosing thoracic ducts, which envelope 

 and almost conceal the abdominal aorta, as they advance 

 forwards, collecting the lymphatics from all surrounding parts, 

 to terminate in their respective subclavian veins. In the alli- 

 gator, four great chylo-lymphatic trunks unite and separate 

 several times, before they collect on each side to constitute 

 two lateral thoracic fasciculi, which receive the neighbouring 

 lymphatics as they advance, and terminate in the two sub- 

 clavians. In the lizard the thoracic duct advances single 

 through part of its course, but divides anteriorly into the 

 usual two branches, before ending in the veins ; in serpents 

 they continue separate from the receptaculum. 



In the class of birds the lymphatics are less wide and sac- 

 culated than in the chelonia, their parietes are more firm ; 

 they are smaller and more numerous than in reptiles, and 

 the valves formed by crescentic folds of their serous lining 

 are more developed. Their course is now generally more di- 

 rect, and their plexuses in the neck are occasionally deve- 

 loped into distinct small lenticular conglobate glands, though 



