CIRCULATORY SYSTEM 141 



aside, thus laying open the pericardial sinus and exposing the 



heart. 



' a. The pericardial sinus is a cavity of considerable size, 

 lying in the dorsal portion of the thorax and re- 

 ceiving the arterial blood from the giUs. 



b. The heart is a polygonal, thick-walled, muscular 



sac lying in the pericardial sinus. If living it 

 wiU be seen to contract rhythmically. It receives 

 blood from the pericardial sinus by three pairs of 

 valvular apertures, the ostia, of which the dorsal 

 pair will be readily seen. The lateral and ventral 

 pairs will be better seen at a later stage of the 

 dissection. 



c. The roots of the arteries are rather small and trans- 



parent, and hence difficult to see. They arise 

 from the two ends of the heart, and should be 

 noticed at the present stage in the dissection, 

 though the arteries themselves are best seen in 



Fig. 35. — Astacus fiuviatilis, var. nobilis. Dissection of a male from 

 the right side. The right side of the body-wall with its appendages, 

 and the right side of the oasophagus, stomach, and mesenteron, have 

 been removed. The thick black line represents the cut edge of the 

 cuticle, (o. H. H.) 



A, endophragmal skeleton. AA, antennary artery. ATT, auditory sac. 

 B, basipodite of the tenth appendage. BI>, aperture of left bile-duct Into the 

 mesenteron. C, cardiac chamber of the stomach. CM, CEecum. CO, cardiac 

 ossicle, CP, carpopodite of tenth appendage. CP 9, carpopodite of ninth 

 appendage. CX, coxopodite of tenth appendage. D, dactylopodite of the 

 same. dA, dorsal abdominal artery. E, eye. G- 1, supra-cesophageal gang- 

 lion. G- 2, sub-oesophageal ganglion, Gr 3, second post-oesophageal ganglion. 

 G 8j last thoracic ganglion. G- 14, last abdominal ganglion giTing ofE posterior 

 ■visceral and other nerves, H, right lateral ostium of the heart. HA, hepatie 

 artery. I, prociodoeum. IS, ischiopodite of the tenth appendage. K, kidney. 

 Ii, liver. IjT, lateral tooth, M, meropodite of the tenth appendage, MS, 

 metastoma. MT, median tooth. ' M 8, meropodite of the eighth appendage. 

 K" 1, N 3 ete. endopodites of first, third, etc, appendages. O A, ophthalmia 

 artery. OC, left para-oesophageal connective : the greater part of the right 

 one has been removed. OE, ossophagus. PL 16, pleuron of the sixteenth 

 segment, PO, pyloric ossicle, PPO, prepyloric ossicle. PK, propodite of 

 the tenth appendage, PTO, pterocard^o ossicle, PY, pyloric chamber of 

 the stomach, P 3, P 4, P 5, protopodites of the third, fourth, and fifth 

 appendages, R, rostrum, S A, sternal artery. S 16, sternum of the sixteenth 

 segment. T, testis : the right anterior lobe has been removed. T 16, tergum 

 of the sixteenth segment, 0, ureter, TJA, aperture of the ureter, TJOO, 

 urocardiac ossicle. VA, ventral abdominal artery. VD, left vas deferens : 

 the right one has been cut off short. VD A, aperture of the left vas deferens, 

 X 1, X 2, etc,, exopodites of first, second, etc., appendages, 20, zygocardiac 

 ossicle, 14, the fourteenth appendage. 



