262 GENERAL ANATOMY. 



heart, and that of the lymphatic trunks with the venous trunks 

 near that organ, in the subclavian veins. But in the points di- 

 ametrically opposite to this double circle, in the capillary sys- 

 tem, the communication is not so obvious. The ancients sup- 

 posed that of the arteries with the veins, but did not believe 

 the communication to be direct. The discovery of the circu- 

 lation of the blood, while it made this communication to be 

 necessarily admitted, still left its mode undecided. We have 

 already seen, that microscopical observations and injections 

 agree in demonstrating this communication, and even showing 

 that it is direct. 



Microscopical observations have demonstrated* it in the 

 transparent parts of cold blooded oviparous animals, in the in- 

 cubated egg of birds, and even in the transparent parts of 

 mammiferous animals. 



Injection has demonstrated it in almost every part of the 

 body of man and animals,! either by forcing the matter through 

 the arteries, or by pushing it through the veins into parts, as 

 the intestine, in which the veins have no valves. 



Some anatomists had even admitted arterio-venous commu- 

 nications between vessels visible to the naked eye, and of a cer- 

 tain calibre; thus Casserius represents them as occurring in the 

 liver, Riolan describes them as happening after a cured aneu- 

 rism, Lealis notices such communications between the sper- 

 matic arteries and veins. These are errors, that is to say, ill- 

 observed facts, which have been contradicted by Albinus and 

 Haller. 



The communications between the arteries and veins are all 

 capillary and microscopical, but it appears, that in cold blooded 

 animals at least, there are some which permit several coloured 

 globules to pass at once, and others a single one only. 



The disposition of these passages of communication has 

 been observed in animals. They consist, sometimes, simply 



* Malpig-hi, be. clt. Leuwenhoeck. be. cit. Spallanzani, ExpsrL sur la 

 circulation, page 255. 



f See particularly: Ruysc/t Thes. anat. Winslow, mem. de Facad. dts 

 sciences. Haller, de Fabric^ corp. human?', vol. i. Mascag-ni. vas. lymph. &fr. 

 prodromo &c. Proehaska, lur. cit. Reissessen, de structure pnhnon. 



