AKTERIES OF MAMMALIA. 



>33 



415 



sheet of pellucid membrane, to which are adherent fine reticulate 

 fibres, mostly affecting a longitudinal direction. It is also fre- 

 quently perforated with small holes, fig. 415, a, a, from which 

 circumstance it is called ' fenestrate.' This homogeneous mem- 

 brane has the property of rolling itself up in the form of a scroll, 

 somewhat like the elastic laminae of the cornea. It is strengthened 

 in many parts by longitudinal anastomos- 

 ing fibres of elastic tissue; and together 

 with the epithelial deposit forms the * inner 

 coat ' of the artery. The ' middle coat ' 

 consists of a fibrous tissue, circularly dis- 

 posed, in layers more numerous as may 

 be the size of the artery and thickness of 

 the coat, fenestrate tissue intervening ; of 

 a reddish-yellow, clearer when fresh than 

 yellow elastic tissue : it consists of bundles 

 of slender fusiform filaments, commonly 

 nucleate, with fine elastic fibres traversing 

 them in a reticulate manner. Acetic acid 

 dissolves the chief substance of the fila- 

 ment, and demonstrates the long staff-shaped nucleus, fig. 416, a, 

 and the ' cell-wall.' This e muscular tissue ' predominates in the 

 smaller arteries ; of which, when treated by soluble reagents, 



Fenestrate membrane. 



416 



417 



Fusiform nucleate filaments, or ' muscular 

 fibre-cells." 1. Natural. 2. Treated with 

 acetic acid. ccvm". 



Small artery with appended corpuscle, 

 from the spleen of a Pig ; treated with 

 soda, and magn. 250 diam. ccvm". 



the coats present the appearance shown in the portion of a splenic 

 arteriole, fig. 417, where c is the outer coat with the sheath 

 of areolar tissue, e the elastic inner coat, and d the dissolved middle 



