214 LABORATORY MANUAL FOR VERTEBRA1E ANATOMY 



vessels, inclosed in the haemal arch. The caudal artery is dorsal, the caudal 

 vein immediately ventral to the artery. 



Dogfish: Probe into the caudal vein. Observe that the probe can be passed 

 either to the right or left, showing that the vein forks at the anus. The two 

 forks are the renal portal veins. Leaving your probe in one of the renal portal 

 veins, locate the kidney in the pleuroperitoneal cavity. It is a long brown 

 organ situated against the dorsal body wall, one on each side of the mid-dorsal 

 line external to the pleuroperitoneum. Slit the pleuroperitoneum along the 

 lateral border near the posterior end of the kidney on the side where your probe 

 is inserted and gently lift the kidney away from the body wall . A space will be 

 found between the kidney and the body wall; into this space your probe has 

 passed. This space is the renal portal vein or sinus. It branches into the 

 kidney and also receives tributaries from the body wall. 



Skate: The kidney has already been exposed. Look along the medial side 

 of the posterior part of the kidney for a vein coming from the vertebral column. 

 Do not injure any ducts on the ventral surface of the kidney. In males the vein 

 in question lies immediately to the dorsal side of the male duct, which will be 

 seen passing along the ventral surface of the kidney to the cloaca. The duct 

 may be lifted from the kidney surface and bent to one side. The vein in question 

 is the renal portal vein. At first it lies along the medial border of the kidney, 

 but soon turns onto the ventral surface of that organ, giving off branches into 

 its substance and receiving tributaries from the body wall lateral to the kidney. 

 The renal portal veins are continuations of the caudal vein; the latter forks at 

 the anus giving rise to the two renal portal veins. The forking is, however, 

 difficult to trace in the skate. 



Reference to Figure 55, page 205, will show that the renal portal veins are the 

 posterior parts of the posterior cardinal veins and that the apparent posterior 

 parts of the posterior cardinal veins of the adult are in reality the subcardinal 

 veins. Whereas in the embryo the blood flows from the subcardinals into the 

 posterior cardinals, in the adult the direction of flow is reversed. The renal por- 

 tal system provides that the blood from the tail must pass into a capillary 

 system in the kidneys from which the blood is re-collected into the subcardinal 

 veins. The purpose of this arrangement is obscure ; it seems to have been disad- 

 vantageous, for the vertebrates later shunted part of this blood into another 

 system and finally abandoned the renal portal system altogether. 



Draw the renal portal system. 



5. The ventral aorta and the afferent branchial vessels. — Turn once more 

 to the pericardial cavity of the specimen. The conus arteriosus runs forward and 

 penetrates the anterior wall of the pericardial cavity. Carefully pick away 

 muscles and connective tissue from the region extending from the anterior end 

 of the pericardial cavity to the lower jaw. In the median ventral line will be 



