XIII.] STRUCTURE OF BLOOD-VESSELS. 123 



tissue, with some elastic tissue not infre- 

 quently arranged in layers, especially at the 

 inner part of the coat. Note the nuclei of 

 the muscle cells (cp. Lesson viiL § 11). 



As a rule in the more peripheral arteries, the 

 middle coat is formed of bundles of muscular 

 fibres separated from one another by a small 

 amount only of connective tissue with elastic 

 fibres. 



2. Take the jugular vein from a freshly-killed rab- 

 bit, cut it open longitudinally, and pin it out 

 with hedgehog quills with the inner surface 

 uppermost on a thin piece of cork ; stream water 

 gently over it for a moment, then pour over it a 

 •2 p. c. solution of nitrate of silver and leave it for 

 five minutes, wash well with distilled water, and 

 expose to light, also in distilled water, until it 

 becomes of a brownish colour : spread it out on 

 a slide with the inner surface uppermost, treat 

 it successively with 60 p. c, 75 p. c, 95 p. c. 

 alcohol, clear and mount it in Canada balsam. 

 Observe the rather jagged dark lines of the 

 cement substance between the cells; the cells 

 form a continuous layer, are more or less elon- 

 gated in a longitudinal direction, and are flat; 

 indications of the nuclei of the cells may be 

 seen, and in some places indications also of the 

 fibres of the muscular coat, as transverse or 

 longitudinal markings caused by a deposition of 

 silver in the cement substance between the muscle 

 cells. If the vein has been left too long in the 



