BLOOD-VASCULAR SYSTEM OF THE LORICATI 41 
which, by the contraction of the trabecule of the auricle, the 
blood from the auricle is forced into the ventricle. In order to 
prevent a back-flow of blood, this passage ¢an be entirely closed 
by 2 auriculo-ventricular valves (Pl. VI, figs. 39 and 4o; and 
Text-fig. 1; A.V.V.), respectively anterior and posterior in 
position and which when closed appear like 2 inverted cups from 
the auricle side, having their inner edges free. These valves 
are formed by the union and a thickening of the outer layer of 
connective tissue from the auricle and the ventricle. 
Venice (Next-nos. pratid 2; Pls.'1, Wand: VI, '‘fias..7, 12, 
39 and 40; Ven.).— The ventricle, which is 42 mm. long by 
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27 mm. wide in this specimen, is shaped something like a 4- 
sided pyramid. Beginning bluntly, it gradually increases in 
width and then rapidly tapers down into a posterior apex. The 
ventricle has one more layer than the auricle. Outside is the 
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