456 APPENDIX. 



f. Pass a probe into the aorta. Introduce scissors behind the 

 septal flap of the bicuspid valve and slit the aorta without injury to 

 the bicuspid valve. 



II. Dissection of the Blood-vessels. 



Preparation and Injection. — A new specimen must be prepared for 

 the dissection of the blood-vessels. The same specimen may be 

 oised, if necessary, for the dissection of the peripheral nervous 

 .system, — one side being used for the blood-vessels, the other for the 

 nerves, — but it is much better to use separate specimens for the two 

 •.systems. 



Inject the femoral artery of the specimen with either five per 

 -cent, formalin, or with the mixture of five per cent, formalin and 

 glvcerine, exactly as for the muscles. Then, without removing the 

 canula or waiting, inject the artery with red starch. This is prepared 

 as follows: 



Mix together equal volumes of vermilion (or red lead), glycerine, 

 and five per cent, formalin. Grind these together in a mortar, so as 

 to destroy the lumps; strain the resulting mixture through fine 

 muslin. This color mixture can be preserved in a closed bottle till 

 it is to be used. Then mix together one volume of dry starch, one 

 and one-fourth volumes of five per cent, formalin, and one-fourth 

 volume of the color mixture. See that no lumps are present. 



Inject the above red starch mass into the femoral artery. It will 

 drive into the veins the formalin already injected, and the arteries 

 will be filled with the red starch. 



The veins need not be injected, as they will be found to be filled 

 with the formalin mixture, colored by the blood, so that they can be 

 traced without great difficulty. 



Dissection of Blood-vessels. — In general the arteries and veins will 

 be traced together. It is an excellent plan to make a sketch of each 

 vessel as it is dissected, showing its origin, branches, and name. 

 This will be a great aid to the memory and will be of much assist- 

 ance in reviewing the vessels. The sketches can later be combined 

 into a well-ordered drawing. The description of each vessel must 

 of course be studied as the vessel is dissected. 



In tracing blood-vessels do not grasp them between the forceps- 

 blades, but handle them by taking hold with the forceps of the con- 

 nective-tissue coats of the vessels. Do not use the scalpel, but pull 

 away the connective tissue and fat with fine forceps, using two pairs 

 of forceps or one forceps and the tracer. 



Variations are especially common in the blood-vessels, and the 

 student must not be surprised to find considerable deviations from 

 the conditions described and figured in the text. These variations 

 usually present nothing new in principle and are easily understood 

 by comparing them with the structures described. 



Directions /or Dissecting the Blood-vessels. — I\Iake a median longi- 



