THE SKATE. 45 



position) the foregoing viscera : they should be brought 

 into view by turning over the latter. 



80. The kidneys (Figs. 18 and 19, k) are also seen 

 when the other viscera are turned aside, as long, dark red 

 bodies, lying one on either side of the middle dorsal line 

 of the posterior end of the body cavity : they are often 

 obscured by the thick pigmented peritoneum which covers 

 them. 



XIII. Make a median longitudinal incision from the 

 anterior boundary of the shoulder girdle to about 

 the level of the second gill cleft : take transverse 

 incisions from both ends of this, and reflect the 

 flaps made, so as to expose the pericardial cavity : 

 note 



8 1. The strong fibrous partition bounding the peri- 

 cardium posteriorly, and separating it from the abdominal 

 cavity. 



82. The heart (Figs. 17, 20, and 21), consisting of a 

 fleshy ventricle (r), from which is given off anteriorly, 

 and somewhat to the right side, the fleshy tubular conus 

 arteriosus (c.a) ; and to the dorsal side of these (beneath 

 in this position) the large thin-walled sub-triangular auricle 

 (//), and posterior to this, the transverse, tubular, transparent 

 sinus venosus (s.v). 



XIV. Remove the skin to a distance of about an inch 

 on either side of the heart, so as to expose the 

 gill-sacs : remove the ventral walls of the latter, 

 so as to expose their cavities. Make out 



83. The five pairs of gill cavities, separated from one 

 another by complete partitions, and opening externally by 

 the apertures already seen. 



84. The red branchial filaments attached to both 

 anterior and posterior walls of all the cavities except the 



