THE COMMON FROG. [chap. 



fectly divided, the blood sent to the lungs would be 

 necessarily a mixture of venous and arterial fluid, 

 and similarly that the blood distributed by it to all 

 the organs and parts of the body is alike a mixture 

 of pure and impure fluid. 



In fact, however, this is by no means the case, and 

 in the frog, in spite of the reception into a single 

 chamber of both venous blood from the body, and of 

 arterial blood from the lungs, special mechanical 

 arrangements effect such a definite distribution of the 

 two sorts of blood, that the unoxygenated fluid from 

 the body is sent to the purifying respiratory surfaces 

 (lungs and skin), and the pure oxygenated blood 

 alone goes to the head and to the brain. 



For the detection of this beautiful mechanism we are 

 indebted to the careful investigations of Ernst Briicke.^ 



The heart of the frog consists of a right and left 

 auricle (divided by a delicate septum), both opening 

 into a single ventricle. From the latter proceeds an 

 aortic root (bulbus aortse) which gives rise to three 

 arterial trunks on each side. 



The first of these, or carotid trunk (i), ends in an 

 enlargement {a) termed the carotid gland, of spongy 

 structure, which gives rise to two arteries, one the 

 lingual (/), the other [c] the carotid which goes to the 

 head and brain. 



The second, or systematic trunk (2) meets its fellow 

 of the opposite side beneath the spine, and thence 



1 " Beitrage zur vergleichenden Anatomic und Physiologic der Gefass- 

 Systemes." In the third vokimc of the " Denkschriften dcr Mathe- 

 matisch-Natur-wisscnchaftlichen Classe dcr Kaiserlichen Akademie der 

 Wissenschaftcn." Vienna : 1 85 2, 



