148 



H. D. SENIOR. 



blend. In this particular Tarpon, the ventricle thus measured 

 is 41 mm. long, and taking 9 mm. as the average length of the 

 conus, the proportion of the conus length to ventricle length, 

 becomes I to 4. 5. Six Amia hearts measured in the same way 

 yield an average proportion of conus to ventricle of I to 1.76. 



The exterior of the conus presents 

 relations which differ in different re- 

 gions. At the mid-lateral line, and 

 ventral to this, the ventricle covers 

 the conus completely. Dorsal to the 

 mid-lateral line, the ventricle recedes 

 rapidly, so as only to overlap the conus 

 for a short distance on either side ; in 

 the interval, the conus is incom- 

 pletely covered by the atrium. The 

 area uncovered by ventricle and at- 

 rium measured back from the bulbus, 

 is about 3 mm. in the midline, and 

 lateral to this about 4 mm., it is cov- 

 ered by visceral pericardium. (These 

 relations are indicated in Fig. 2.) 



The conus is everywhere overlaid 

 by a distinct layer of loose connec- 

 tive tissue, which separates it from 

 the structures which cover it, and 

 renders its outline very distinct in 

 sections of the heart. Owing to the 

 looseness of its connection with 

 neighboring structures, the entire 

 conus is easily exposed from the 

 outside by incising the pericardium 

 at the base of the bulbus, and strip- 

 ping it away from the adjacent parts 

 of the ventricle and atrium. 



The conus valves are disposed in two transverse rows. Each 

 row consists of a right and left cusp symmetrically placed with 

 regard to the median dorso-ventral plane of the conus. Seen 

 rom the lumen of the heart (as in Fig. i) the valve cusps of 



FIG. 2. Diagrammatic right 

 lateral surface-view of bulbus, 

 conus and ventricle. The atrium 

 is represented as incised mesi- 

 ally, and the right half removed 

 (natural size). The line across 

 the conus indicates the site of re- 

 flection of visceral pericardium 

 on to the atrium. The broken 

 line indicates the site section in 



Fig- 3- 



