692 KEPTILIA. 



same manner as in other Yertebrata. The spleen (fig. 340, 1) is gene- 

 rally more or less closely connected with the stomach ; and the large 

 vein derived from it, being joined by those proceeding from the other 

 viscera of the abdomen, forms the trnnk of the portal vein (m), which 

 soon divides again into numerous branches that ramify in the substance 

 of the liver. 



(1936.) The lymphatic and lacteal systems are very important parts 

 of the economy of these creatures ; and, from the large size of the 

 absorbent vessels, their disposition is more easily traced in the class 

 before us than in any other. The principal trunks surround the aorta 

 and other large blood-vessels, and communicate very extensively with 

 the veins in different parts of the body. From the imperfect condition 

 of the valves in their interior, the lacteals of many tribes may be readily 

 injected from trunk to branch, and when thus filled with mercury, 

 they are found to spread out between the coats of the intestines like a 

 dense network of silver. 



(1937.) But the most remarkable circumstance connected with the 

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

 Miiller of Berlin*, of a system of lymphatic hearts destined to propel 

 the products of absorption from the chief lymphatic 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 lym- 

 phatic 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. 



(1938.) 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. 



(1939.) Fishes respire water by means of gills. Reptiles, breathing 

 a lighter medium, are provided with lungs membranous bags, into 

 which the external element is freely admitted, and again expelled in a 

 vitiated condition, its oxygen having been employed 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. 



(1940.) This important difference between Fishes and Reptiles as 

 relates to their mode of respiration would seem, at first sight, to draw 



* Vide Berlin Annals for 1832 ; and also Panizza, sopra il Sistema Linfatico dei 

 Kettili. fol. Pav. 1833. 



