9. INTERNAL ANATOMY AND PIIYSIOLOGY
259
lumen of the pericardium, the bag inside which the heart is contained,
connects with the heart cavity by way of two pairs of ostia (Fig. 95))
the more dorsally situated pair being slightly anterior to the other. The
heart possesses an extremely complex muscular system, some of the
largest components-the trabecula (Fig. 95)-of which traverse the
lumen from the dorsal lateral to the ventral median areas. The wall
of the heart is composed of two layers, the outer layer, which completely surrounds the inner layer, being of connective tissue and connected to the pericardial wall by strands of connective tissue. The
asr
rnac
qsl
I
FIG. 96. Arterial system of Meganyctiphanes lzorvegica from the dorsal and lateral aspects.
ad, aorta descendens ; all, left arteria lateralis ; alr, right arteria lateralis ; asl, left
arteria abdominalis superior ; asr, right arteria abdominalis superior ; bg, vessels to
blood gland ; h, heart ; ha, left hepatic artery ; iv, intestinal artery from left arteria
lateralis; rnac, median aorta cephalica; mp, artery to mouthparts; pl. p5, left-hand
branches to pleopods 1 and 5 respectively; ph, photophore receiving branch from
aorta descendens ; 54, fourth abdominal segment ; sb, small dorsal blood vessel
supplying muscles and epithelium. (After Mauchline, 19588.)
inner layer of the wall of the heart is muscular. The most detailed
account of the histology of the heart is that of Colosi (1920) on
Nematoscelis megalops.
The main arteries are shown in Fig. 96. Three arteries run anteriorly
to supply the anterior thoracic region, the head, eyes, mouthparts,
antennae, and antennules. A branch from the left arteria lateralis
(Figs 96, 97) supplies the alimentary canal and stomach. Ventral to the
origin of these three vessels are found the paired hepatic arteries (Figs
96,97) which descend anteriorly to their respective halves of the hepato-
259
lumen of the pericardium, the bag inside which the heart is contained,
connects with the heart cavity by way of two pairs of ostia (Fig. 95))
the more dorsally situated pair being slightly anterior to the other. The
heart possesses an extremely complex muscular system, some of the
largest components-the trabecula (Fig. 95)-of which traverse the
lumen from the dorsal lateral to the ventral median areas. The wall
of the heart is composed of two layers, the outer layer, which completely surrounds the inner layer, being of connective tissue and connected to the pericardial wall by strands of connective tissue. The
asr
rnac
qsl
I
FIG. 96. Arterial system of Meganyctiphanes lzorvegica from the dorsal and lateral aspects.
ad, aorta descendens ; all, left arteria lateralis ; alr, right arteria lateralis ; asl, left
arteria abdominalis superior ; asr, right arteria abdominalis superior ; bg, vessels to
blood gland ; h, heart ; ha, left hepatic artery ; iv, intestinal artery from left arteria
lateralis; rnac, median aorta cephalica; mp, artery to mouthparts; pl. p5, left-hand
branches to pleopods 1 and 5 respectively; ph, photophore receiving branch from
aorta descendens ; 54, fourth abdominal segment ; sb, small dorsal blood vessel
supplying muscles and epithelium. (After Mauchline, 19588.)
inner layer of the wall of the heart is muscular. The most detailed
account of the histology of the heart is that of Colosi (1920) on
Nematoscelis megalops.
The main arteries are shown in Fig. 96. Three arteries run anteriorly
to supply the anterior thoracic region, the head, eyes, mouthparts,
antennae, and antennules. A branch from the left arteria lateralis
(Figs 96, 97) supplies the alimentary canal and stomach. Ventral to the
origin of these three vessels are found the paired hepatic arteries (Figs
96,97) which descend anteriorly to their respective halves of the hepato-