THE VEINS. 93 
b. Note the character of the heart’s pulsations—a regularly 
alternating series of contractions and dilatations, 
¢, Note further that in each contraction or systole of the 
heart all four divisions of the heart contract, but not 
simultaneously. The sinus venosus_ contracts first, 
then the two auricles, then the ventricle, and finally 
the truncus arteriosus. ere 
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Fig. 4. Diagrammatic figure of the venous system of the frog, from the 
_ right side. 
a, stomach: a.v, anterior abdominal vein: 6, bladder: 6.v, brachial vein : 
c.l, cloaca: ¢.v, cardiac vein: d, large intestine: e, liver: e.v, external 
jugular vein : f.v, femoral vein: g, gall bladder: h, spleen: %.c, inferior vena 
cava: i.v, innominate vein: j.v, internal jugular vein: l.p, left pelvic vein : 
m.v, musculo-cutaneous vein : 0, kidney: p.v, hepatic portal vein: 1.p, right 
pelvic vein: 7.v, right renal portal vein: s, sinus venosus: 8.¢, sciatic vein: 
$.v, subclavian vein: t, tongue: t.a, truncus arteriosus: wu, right auricle: 
v, ventricle : v.v, vesical veins. 
The veins should be dissected before the arteries because, as 
a rule, they lie nearer the surface and are therefore met with 
first. The veins are further distinguished from the arteries by 
their larger size, thinner walls, and darker colour, due to the 
blood being seen through their walls. 
Dissect from the ventral surface. In cleaning a vein take hold 
with the forceps, not of the vein itself but of the tissue surrounding 
it: and take especial care not to prick the vein, as by doing so you 
allow,.the blood to escape and obscure the dissection, and also 
