17G 
ANODONTA — CIRCULATORY SYSTEM. 
and tlie foot, and to wliich many other vessels converge. It is 
continnous witli, hnt separalile from, the pedal sinus by the powerful 
sphincter muscle, known as Keber’s valvule, the action of which 
renders possible the rapid turgescence of the foot. From the vena- 
ca^'a the greater part of the Idood flow's through and irrigates the 
renal organ and is then gathered up into the afferent branchial trunk 
at the common base of the gills and from thence distributed by smaller 
vessels to become arterialized by respiration wdthin the branchial 
Fig. 31 .). — Anodonia cygncn^ with the foot and the right mantle lobe removed, injected from 
auricle, to further illustrate the circulatory system, and more especially the efferent pallial, branchial 
and related vessels, and the capillary circulation within the pericardial gland. No note is taken of 
the extensive series of pallial sinuses connected with the efferent branchial trunk (after Howes). 
n. auricle of the heart ; a.ad. anterior adductor ; a.f>. anterior protractor muscle ; e/.hr.v. efferent 
liranchial veins returning blood to auricle ; e/.hrj, efferent branchial trunk ; ef p,v. efferent pallial 
veins; pc. pericardial chamber; //./. plexus within pericardial gland ; r. rectum traversing vent- 
ricle ; V. ventricle of the heart opened to show the rectum and tlie auricular orifice. 
I.imclliv, flowing as arterial l)lood into the efferent hrancliial arteries, 
placed along the junction of the secondary limb of the inner gills 
with the body wall, and also at the junction of the secondary limb of 
the outer gills with the pallial lobes, where the blood combines with 
that brought by the efferent pallial vessels from the mantle and pro- 
ceeds thence to the auricle, either directly or by way of the pericardial 
gland. Some venous blood, however, passes direct to the branchial 
arteries or to the auricles without undergoing the })ortal circulation 
through the kidneys, and a much larger (quantity, which has been 
]iurifleil within the mantle lobes, does not enter either the renal organs 
or the hranchia', hut, mixed with some from the outer gills, undergoes 
a portal circulation within the i)ericardial gland before entering 
the auricles. 
Although the vascular mantle lobes largely assist in the oxygenation 
of the blood, the respiratory organs are normally constituted by the 
branchial lamellm or gills, which arise from a longitndinal vascular 
