214 CLASS XV. 



which are loaded with fat, in many saurians, and membranous 

 filaments, also containing fat, in the serpents, somewhat resemble 

 them. 



The lymphatics seem in reptiles to be destitute of valves, 

 except at the place where they open into the veins. They are 

 highly developed, form numerous plexuses, and here and there 

 sacciform expansions, but no lymphatic glands. The large blood- 

 vessels are often surrounded by wide lymphatics or by lymphatic 

 plexuses, as by a sheath. There are two thoracic ducts, or the 

 single thoracic duct divides anteriorly into two branches, which 

 deliver the chyle, mixed with the lymph, into the subclavian veins, 

 or anterior venous stems. In different reptiles pulsating lymphatic 

 spaces have been discovered, which are in connexion with veins, 

 and force the lymph into them. In the frog, and in many other 

 reptiles, two such lymphatic hearts are situated on the back, 

 behind the joint of the thigh-bone, immediately beneath the skin ; 

 they empty their lymph into a branch of the ischiadic vein. These 

 pulsating cavities occur also in lizards and tortoises, and in 

 serpents they lie under the vertebra in front of the commence- 

 ment of the tail. In the frog, besides these lymphatic hearts, there 

 are two other anterior, which lie under the scapula on the trans- 

 verse processes of the third vertebra 1 . 



In most reptiles the two ventricles of the heart are united to 

 form a single cavity, or are only imperfectly separate. Invaria- 

 bly a portion only of the venous blood is distributed to the 

 lungs, whilst another portion, mixed with arterial blood, is sent 

 to the different parts of the body. The heart is thus at once 

 both arterial and venous, and not, as in fishes, solely venous ; 

 but the arterial part is not, or not so completely, distinct from 

 the venous, as in the birds and mammals. 



1 Compare the splendid work of PANIZZA, Sopra il Sistema linfatico dd Retiili 

 Ricerche zootomiche, Pavia, 1833, folio- The work of RUSCONI on the same subject is 

 known to me only from extracts (see ex. gr. DUVERNOY Ann. des Sc. nat. 3ieme SeYie, 

 1847, VII Zoologie, pp. 337 381). The pulsating lymphatic hearts were first discovered 

 in the frog by J. MUELLER, and almost simultaneously by PANIZZA, in this and other 

 reptiles; see also E. WEBER on similar lymphatic hearts in Python, MUELLER'S Archiv, 

 II. 1835, s. 535 547, Taf. 13, figs. 5 10. They were last demonstrated in tortoises, 

 also by MUELLER; see Ab/i. der Berl. Akad. der Wissenschaften, Physik. Klasse, 1839, 

 a. 31 33, with fig. 



