452 SANGUIFEROUS SYSTEM. 



sacculated, and provided with a distinct muscular coat con- 

 sisting of strong circular fibres. It is attached by transverse 

 muscular bands, it terminates suddenly at its anterior part 

 in a narrow membranous aorta, and it gives off numerous 

 lateral ramifying arteries from its saccular enlargements ; it 

 originates posteriorly from the union of several large return- 

 ing venous trunks ; several of its branches are observed to 

 ramify minutely through the granular fatty substance of the 

 abdomen, and others are derived from the pulmonary sacs. 

 From the anterior part of the aorta, as shown by Treviranus, 

 two large lateral trunks diverge on each side, and the dimi- 

 nished median artery continues forwards to the head as in the 

 myriapods; he has likewise observed two lateral venous canals 

 extending along the abdomen. I have found four compart- 

 ments of the heart in spiders as in the common tegenaria, 

 which are each provided with distinct valves, and with 

 lateral narrow depressions or openings, as in the heart 

 of the scorpion and in that of insects. The first or 

 posterior chamber is very small and narrow, situate nearly 

 above the anus, provided with opaque muscular parietes, 

 and receives the thin membranous trunks of numerous 

 minutely ramified veins. The second compartment is 

 much larger and longer than the first, the third is the longest 

 and the broadest division of the heart; and the fourth 

 or anterior compartment, which is situate immediately behind 

 the junction of the abdomen with the cephalo-thorax, is as 

 short as the first, but the most thick and muscular in its 

 parietes. These divisions of the heart give off lateral 

 branches; they are dilated at their line of junction where the 

 valves are placed, and the narrow lateral slits which have a 

 dorsal aspect ; and they extend along the dorsal part of the 

 abdomen, immediately beneath the integuments, from the 

 anus to the cephalo-thorax where the short thin membranous 

 aorta commences. 



The heart of the scorpion is, on the contrary, confined 

 to the anterior part of the body, or alvithorax, and con- 

 sists of a greater number of compartments than in the 

 spiders, amounting here to six or eight distinct cavi- 

 ties. These cavities are furnished with lateral suspensory 

 muscular bands, and strong muscular opaque parietes, com- 

 posed chiefly of transverse fibres ; they are dilated at their 



