564 REPTILTA. 



(625.) But the most remarkable circumstance connected with 

 the absorbents of this class of animals is the discovery, made by 

 Professor M tiller of Berlin,* of a system of lymphatic hearts 

 destined to propel the products of absorption from the chief lym- 

 phatic trunks into the veins. In the Frog four of these pulsating 

 cavities are easily displayed by simply raising the skin covering the 

 regions of the body where they are situated. The posterior pair 

 of hearts are appendages to the lymphatic trunks which convey 

 the absorbed fluids derived from the hinder extremities into the 

 ischiadic veins : they are situated on each side midway between the 

 extremity of the long bone which represents the os coccygis and 

 the hip-joint, and are placed immediately beneath the integument. 

 They each consist of a single cellular cavity, and pulsate regularly ; 

 but their pulsations are quite independent of those of the heart, 

 neither are the contractions of the two lymph-hearts synchronous 

 with each other. 



Another pair of these contractile cavities is situated beneath the 

 posterior margin of the scapula close to the transverse process of 

 the third vertebra : this pair forces the contents of the lymphatics 

 of the anterior portions of the body into the jugular veins. 



(626.) Fishes respire water by means of gills. Reptiles, 

 breathing a lighter medium, are provided with lungs, membra- 

 nous bags into which the external element is freely admitted, and 

 again expelled in a vitiated condition, its oxygen having been em- 

 ployed in renovating the blood which circulates in an exquisite 

 network of delicate vessels, that ramify in rich profusion over the 

 walls of the pulmonary chamber. 



This important difference between Fishes and Reptiles as 

 relates to their mod^ of respiration would seem, at first sight, to 

 draw such a distinct line of demarcation between these two great 

 classes of Vertebrata that it would be impossible for the most 

 superficial zoologist to confound one with the other, or to be for 

 a single moment at a loss in attempting to assign to any creature 

 belonging to either of these divisions of the animal world its pro- 

 per position ; indeed, to mistake an air-breathing Reptile for a Fish 

 properly so called, would appear to be an error which the most 

 ignorant naturalist could hardly be in danger of committing. 



We have, however, again and again had opportunities of observ- 

 ing how nearly animals of neighbouring classes approximate each 



* V r ide Berlin Annals for 1832; and also Panizza, sopra il sistema linfatico dei Ret- 

 tili. Fol. Pav. 1833. 



