296 EXAMINATION OF ARTEBIES AND VEINS. 



301. Examination of arteries and veins. — Tlie 



structure of arteries and veins may be well studied 

 ie any of the smaller vertebrate animals, especially in 

 the frogs. In mammalia beautiful specimens may be 

 obtained from the monse. Those in the mesentery, 

 the pleura, and pericardinm may be subjected to ex- 

 amination "vvithout difficulty, but the smaller arteries 

 and veins of the pia mater, or vascnlar membrane of 

 the brain, and those of the folds (choroid plexuses) 

 of the same membrane in the cavities (ventricles) of 

 the brain are more free from connective tissue and 

 can be easily isolated. 



I have obtained beautiful specimens of the muscu- 

 lar fibre-cells arranged circularly round the small 

 arteries by injecting the vessels with plain size, and 

 gradually increasing the force so as to distend them 

 as much as possible without rupture. In this manner 

 the cells are as it were, gradually unravelled. When 

 cold, thin sections may be very easily made in 

 various directions, and even isolated fibre-cells can be 

 obtained. The arrangement of the muscular fibre- 

 cells in the smaller vessels, is well seen in the small 

 arteries from the fi'og and newt. See fig. 4, Plate 

 XVI and Plate XVII. 



The bioplasts are to be demonstrated in specimens 

 prepared with carmine fluid as described in § 68. 

 I have made some very satisfactory preparations by 

 injecting the vessels first with carmine fluid and after- 

 wards with Prussian blue fluid, as described in 

 " How to Work with the Microscope," 3rd edition, 

 § 377, page 304. 



The arrangement of the numerous nerve-fibres dis- 

 tributed to the small arteries and veins may be 

 demonstrated in the frog with the greatest distinct- 

 ness, and in connection with the small vessels which 

 supply the viscera numerous ganglia will be found 

 from which bundles of nerve-fibres may be traced 

 in difierent directions. These often form plexuses 



