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alias Cstia 
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ARACHNIDA—XIPHOSURA CHAP. 
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Pees 
Fig. 154. —A_ sagittal section of Limulus, 
seen from the right side, somewhat smaller 
than natural size. After Patten and Reden- 
baugh. 
All the prosomatic appendages, except 
the chelicera (4) and chilarium (33) of the 
right side, are omitted. The genital oper- 
culum (32) and the five gills (28) are repre- 
sented. 
The muscles are omitted except the fibres 
running from the occipital ring to the pos- 
terior side of the oesophagus, the chilarial 
muscles, the sphincter ani (27), and the 
levator ani (24). 
The endosternite (34), with the occipital 
ring and the capsuliginous bar, is seen from 
the side, and the positions of the abdominal 
endochondrites (31) are indicated. 
The mouth (1) leads into the oesophagus, 
which passes through the brain to the 
proventriculus (12). A constriction, which 
marks the position of the pyloric valve, 
separates the proventriculus from the in- 
testine (23) which passes posteriorly to the 
anus (26). A pair of hepatic ducts (15) 
enter the intestine opposite the endo- 
cranium. 
The heart (16) surrounded by the peri- 
cardial sinus lies above the intestine. The 
pericardium is shown between the heart 
and the intestine. The ostia (17) of the 
heart and the origins of the four lateral 
arteries (19) are indicated; the frontal 
artery (13) and the aortic arches (14) 
curving down to the brain, arise from the 
anterior end of the heart; the superior 
abdominal artery and the opening of the 
collateral artery into it are shown. 
The brain surrounding the oesophagus is 
seen in side view upon the neural side of the 
endosternite (34). The ventral cord (35) 
passes through the occipital ring into the 
abdominal region. The anterior commis- 
sure (3), with the three rostral nerves (2) 
innervating the rostrum, or labrum, and 
four of the post-oral commissures, are re- 
presented. 
The cheliceral nerve with the small 
external pedal branch is shown entire, but 
the next five neural nerves are cut off. 
The chilarial nerve, the opercular nerve, 
and the five branchial nerves, enter their 
respective appendages, the two former pass- 
ing through the occipital ring. 
From the fore-brain the three olfactory 
nerves (5) pass anteriorly to the olfactory 
organ ; the median eye-nerve (10) passes to 
the right of the proventriculus (12) to the 
median eyes (11) ; the lateral eye-nerve (7) 
passes forward and is represented as cut off 
opposite the proventriculus. The lateral 
nerve (9) or first haemal nerve is also cut 
