454 SANGUIFEROUS SYSTEM. 



chial arteries, (E. e. e.) originating from these wide membra- 

 nous sinuses on each side, distribute the whole venous blood 

 of the system over the innumerable minute laminae of the 

 gills, and from these it is collected by the branchial veins, 

 (133. E./. /.) to be transmitted to the heart. The branchial 

 arteries follow the outer margin, and the returning veins the 

 inner margin of the gills, and the united trunks of the latter 

 vessels convey the arterialised blood, by a single orifice on each 

 side, into the large median muscular ventricle. (133. E. g.) 



The heart, as in other articulata, is situate in the middle 

 of the back, as seen in the lobster, (Fig. 119. A. e. B. g,} and 

 consists of a single systemic muscular cavity, most concen- 

 trated in form in the decapods, and generally elongated like 

 a dorsal vessel on the inferior orders ; its thick parietes are 

 composed of interlaced muscular fibres, they present internal 

 fleshy columns, there are semilunar valves at the orifices of 

 the great vessels, and the heart is connected, as usual, with 

 the neighbouring parts by muscular bands. From the anterior 

 and upper margin of the heart arise three arterial trunks, (133. 

 E. 1. i. h. 119. B. h. h. i.) the two lateral of which send 

 branches to the genital organs and the stomach, and termi- 

 nate in the two antenna! arteries proceeding to the outer arid 

 inner pair of these organs, and the median vessel, (1 19. B. 

 d.) advancing over the stomach to the pedunculated eyes, 

 divides into the two ophthalmic arteries which supply these 

 organs. From the lower and anterior part of the heart, the 

 hepatic arteries (119. A. g.} originate by a single or double 

 trunk according to the divided condition of the liver through 

 which they ramify ; and from the lower and posterior part of 

 the same muscular cavity arises the grea,t sternal artery (119. 

 A. k.) which, after descending to the sternum and dividing 

 into an anterior, (119. A. /.) and a posterior (119. A. m ) 

 trunk, supplies most of the musculo-cutaneous parts on the 

 ventral region of the body, and gives off laterally the brachial 

 arteries to the locomotive organs. From the middle of the 

 posterior margin of the heart is given off the great posterior 

 median systemic artery, (119. A. h. B. k. 133. E. k.) which, 

 extending backwards along the median and dorsal part of the 

 trunk, sends off numerous branches on each side to the neigh- 

 bouring organs, and bifurcates over the colon before distri- 

 buting its terminal branches on the muscles of the tail (1 19. 

 A. i. B/.) 



