Text-book of comparative anatomy . l vesicles ; vd,branches arising in each segment from dro-sal vessel; vv, ventral vessel; vsn, subneural the first pair of lateral vessels of the vessel; rbl lateral vessels of the ventral d!ord :1-11 • • bm, ventral chord; h, contractile vascular loops dorsal vessel, which latter maintain a (hearts) between the dorsal and ventral vessels. communication between the dorsal ves-sel and the sub-neural vessel. The ventral and dorsal vessels give off branches tothe extreme anterior end of the body, which ramify in the body wall and ventral vessel furth
Text-book of comparative anatomy . l vesicles ; vd,branches arising in each segment from dro-sal vessel; vv, ventral vessel; vsn, subneural the first pair of lateral vessels of the vessel; rbl lateral vessels of the ventral d!ord :1-11 • • bm, ventral chord; h, contractile vascular loops dorsal vessel, which latter maintain a (hearts) between the dorsal and ventral vessels. communication between the dorsal ves-sel and the sub-neural vessel. The ventral and dorsal vessels give off branches tothe extreme anterior end of the body, which ramify in the body wall and ventral vessel further divides at its anterior end into 2 branches, which pene-trate to the brain and so form an cesophageal ring. The contractile part of theblood-vascular system possesses muscular walls. XiliUthys scolopcndroidcs (Fig. 167) may be taken as an example of a Polyclt«t<i,<with homouomous segmentation of the body. We find here the two most importanttypical vessels, the dorsal and the ventral. Both lie close to the wall of the. 252 COMPARATIVE ANATOMY CHAP. intestine. From the posterior end of the pharynx to the end of the body the dorsalvessel gives rise in each segment to a pair of lateral vessels, which run to the bodywall and especially to the dorsal branch of the parapodia and there ramify. Soon •t after its rise out of the dorsal vessel each lateral vessel gives off a branchto the enteric wall, this branch thereforming a rich vascular network. Atthe foremost end of the mid-gut thedorsal vessel shows a slight swelling ;it then leaves the intestine and runsalong the inner side of the body wallin the region where the pharynx liesto the extreme anterior end of thebody. It here divides into 2 branches,which run backwards, to pass into theanterior end of the ventral vessel atthe posterior end of the pharyngealregion. The departure from thegeneral plan of the principal vesselsin the pharyngeal region is evidentlycaused by the great development ofthe pharynx. If they lay as
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
