Vascular System of Bdellostoma dombeyt. Be: 
the gill plate. Their general direction is parallel to the axis 
of the gill, and perpendicular to the walls of the gill pouch. 
These smaller vessels break up into capillaries, which ramify 
between the thin epithelial walls of the respiratory gill leaf- 
lets. In this region an extensive capillary network is formed, 
and anastomoses between the larger vessels are also common. 
Toward the opposite (7. e. the inner) attached edge of the 
gill plate, and in the free central margins, the capillaries 
again unite to form larger vessels. These efferent branchial 
vessels converge on the inner wall of the gill pouch in much 
the same way as they are distributed in the outer wall. They 
unite under the muscular layer into sinuses and vessels which 
finally unite to form the efferent branchial artery of each gill 
pouch. This vessel leaves the gill wall just above the internal 
gill passage. (Fig. XIX, ef, br.) A diagrammatic represen- 
tation of the branchial circulation is shown in Figure XIII, 
which respresents the vascular distribution in a plane parallel 
to the gill axis. Figure IX shows a drawing of a section 
of an injected gill made perpendicular to the axis of the gill, 
and near its center. The low magnification, fails to give an 
adequate idea of the great complexity in the formation of the 
gill leaflets. Figures VIII and XIV represent small portions 
of these leaflets magnified to show the capillary vessels, which 
are composed of a single layer of epithelial cells. The larger 
vessels have walls composed of three layers,—an outer layer 
of connective tissue, a middle layer of circular muscle fibers, 
and an inner simple endothelial layer. 
The efferent branchial arteries (Figs. XVIII, XIX, XX, ef, 
br) arise from the inner face of each gill pouch, just above 
the internal gill passage (gpi). Each efferent vessel extends 
upward and inward toward the median line. In the posterior 
region each vessel ascends just behind a “gill constrictor” 
muscle, then turns forward immediately adove it and joins 
the overlying common carotid just anterior to the muscle. 
There are never /wo efferent vessels for each gill-pouch, as is 
commonly the case in Bdellostoma forstert. All the efferent 
branches of each side open into the corresponding lateral 
common carotid. 
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