BLOOD-VASCULAR SYSTEM OF THE LORICATI 



41 



which, by the contraction of the trabecuhe of the auricle, the 

 blood from the auricle is forced into the ventricle. In order to 

 prevent a back-flow of blood, this passage can be entirely closed 

 by 2 auriculo-ventriadar valves (PI. VI, iigs. 39 and 40; and 

 Text-fig. I ; 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. 



Ventricle (Text-figs, i and 2 ; Pis. I, II, and VI, figs, i, 12, 

 39 and 40; Ven.). — The ventricle, which is 42 mm. long by 



Ven. 



B.Art. 



Fig. 2. 



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 laver than the auricle. Outside is the 



