PRACTICAL DIRECTIONS. 461 



inject the fluid. This will pass into the spaces in the connective 

 tissue of the pad, which will swell up, and the colored fluid will pass 

 from the connective-tissue spaces into the lymphatics. Pressure must 

 be maintained with the syringe for a considerable time, — fifteen 

 minutes to a half-hour for a good injection of the main trunks of the 

 lymphatics of the limbs. The movement of the fluid should be 

 facilitated by pressing and manipulating the limb at the same time 

 with the hand, — in such a way as will tend to drive the fluid 

 proximad. 



The lymphatics of the head may be injected in a similar manner, 

 the canula being introduced into the upper and lower lip, or into 

 the bare surface at the end of the nose. 



The internal lymphatic vessels may be injected by injecting the 

 lymphatic glands with which they are connected. This may con- 

 veniently be done as follows: Draw out to a fine point the tip of an 

 ordinary pipette or medicine-dropper. The point should be fine, 

 but should taper rapidly in a conical fashion, so that when the point 

 is inserted the part of the glass tube behind it will close up the 

 opening. 



Fill the pipette with soluble Prussian blue; insert the point into 

 the gland, and inject the fluid slowly. The lymphatic vessels passing 

 from the glands will be filled. By injecting thus the large lymphatic 

 gland ("pancreas Aselli ") in the mesentery, the abdominal lym- 

 phatics, the receptaculum chyli, and the thoracic duct may be 

 injected. 



By using thin gelatine colored with Prussian blue as an injecting 

 fluid permanent preparations may be obtained ; of course the 

 process of injection is then less simple, and should be looked up in 

 some manual of methods. 



NERVOUS SYSTEM. 



I. The Spinal Cord (p. 335). 



Use the specimen on which the muscles were dissected. (Or if 

 the peripheral nerves are not to be dissected on the specimen used 

 for the blood-vessels, that may be employed.) 



Make a longitudinal dorsal median incision of the skin, between 

 the back of the head and root of the tail. Reflect the skin for one or 

 two inches on each side of the incision and cut away the muscles 

 covering the neural arches of the vertebrae from the third cervical to 

 the seventh or eighth thoracic inclusive. 



Remove with bone-forceps the neural arch of one of the last 

 cervical vertebrae and find the spinal nerve emerging from the inter- 

 vertebral foramen. Isolate the nerve for a short distance, then 

 proceed craniad, removing the neural arches on one side and isolat- 

 ing the nerves until the third has been uncovered. The ganglion of 

 the second nerve should be sought among the muscles on the dorsal 

 surface between the atlas and axis, and after it has been isolated the 



