14 GUIDES FOR VERTEBRATE DISSECTION 



Judging from the attachment of the mesovaria are the ovaries to 

 be regarded as medial or lateral to the mesonephroi? 



Running along the ventral surface of each mesonephros, near 

 the medial side, is a slender tube (larger in the sexually mature 

 fish), the oviduct or Miillerian duct. Trace this forward to the 

 anterior end of the liver and thence ventrally to its antero- 

 ventral surface and see the broad opening the ostium tubae 

 by which the Miillerian ducts of the two sides open into the 

 metacoele. 



Insert the point of the scissors into the anus and cut forward 

 as directed for the male. Note the same sudden transitions 

 between rectal and cloacal surfaces and the abdominal pores. 

 See also the urogenital papilla in the dorsal cloacal wall, with a 

 urinary opening at its tip and with the openings of the oviducts 

 on either side. Trace the connection of these ducts with the 

 parts farther forward. 



Cut off the tip of the urinary papilla. A single cavity will be 

 found. With probe and scissors trace this forward to its division 

 into two Wolffian (urinary) ducts each of which may be traced 

 parallel to and dorsal to the Miillerian duct of the same side. 



Sketch the urogenital system as far as made out. 



Circulatory Organs. In the cut surface of the part of the 

 liver which remains in position see the large vessels, the hepatic 

 veins. With probe and scissors lay several of these open, follow- 

 ing them forward to a pair of large sacs, the hepatic sinuses, 

 just in front of the liver and between it and the thin wall, the 

 septum transversum (or false diaphragm) which bounds the 

 metaccele in front. Also examine the septum transversum for 

 an opening of the pericardio-peritoneal canal, dorsal to the liver. 



On either side, in the lateral wall of the metacoele, is a large 

 lateral abdominal vein. Trace it forward into the region of the 

 septum and backwards into the region of the hind limb. 



Carefully cut through the ventral half of the septum trans- 

 versum and the ventral wall of the body, from the metacoele as 

 far forward as the level of the second gill-slit. This lays open 

 the large pericardial cavity containing the heart. Cut away the 

 ventral wall of the cavity so as to permit a good view of its 

 contents. The cavity is seen to be lined with a smooth mem- 

 brane, the pericardium, comparable to the peritoneum of the 

 metacoele. 



