Text-book of comparative anatomy . 144.—(Esophageal ring with diverging nerves of Hirudo, enlarged (after Hermann).r/, Brain; so, cesophageal commissure; 6</i, first ganglion of the ventral chord (infra-cesophagealganglion); by-2, second ventral ganglion. connected by 2 commissures, the cesophageal commissures, whichembrace the fore-gut between them. The anterior end of the intestineis thus surrounded by a nerve ring, the so-called cesophageal ring,which enters the brain dorsally, and the first ganglion of the ventralchord ventrally (Figs. 144, 146). The brain (supra-oesophageal gan-glion),
Text-book of comparative anatomy . 144.—(Esophageal ring with diverging nerves of Hirudo, enlarged (after Hermann).r/, Brain; so, cesophageal commissure; 6</i, first ganglion of the ventral chord (infra-cesophagealganglion); by-2, second ventral ganglion. connected by 2 commissures, the cesophageal commissures, whichembrace the fore-gut between them. The anterior end of the intestineis thus surrounded by a nerve ring, the so-called cesophageal ring,which enters the brain dorsally, and the first ganglion of the ventralchord ventrally (Figs. 144, 146). The brain (supra-oesophageal gan-glion), whose composition out of 2 lateral halves connected by trans-verse commissures can generally be clearly seen, lies originally in thefirst, the cephalic or oral segment. The anterior ganglion, or ratherdouble ganglion, of the ventral chord (infra-cesophageal ganglion)probably originally belonged to the second segment of the remaining double ganglia of the ventral chord follow the infra- 220 COMPAEATIVE ANA TOM Y cesophageal ganglion, one in each segment. The 2 ganglia of eachdouble ganglion are connected together by short transverse commis-issures, and with the corresponding ganglia of the preceding andsucceeding double ganglia by longitudinal commissures. Besides the cesophageal commis-sures nerves proceed from the brainto the integument and the sensoryorgans of the head; and from theganglia of the ventral chord nervessupply the integument, sensory organs,and musculature of the segments towhich they belong. The musculature of the fore-gut(pharynx, proboscis, etc.) is providedwith nerves arising either direct fromthe brain or from the oesophagealcommissures. These nerves are calledFIG. or (sucker) gan- cesophageal nerves (often also nervigiion of Hirudo, -with preceding gan- vagi), and the plexus they form in the fore-gut is called the cssophag-eal nervous system. In the most various divisions there is also a furtherplexus of ganglionic cells and
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
