EXPLANATION OF THE PLATES. 195 



nally, and which are more numerous and closer together towards 

 its internal limit. Between these elastic fibres are connective 

 fibres which grow pale and break down under the action of 

 acetic acid, leaving a hyaline mass (3). 



FIG. VII. Middle coat of a branch of the artery occupying 

 the fissure of Sylvius ; it is composed entirely of muscular fibres, 

 no traces of elastic fibres being visible. 



FIG. VIII. Four muscular fibres from the basilar artery. 

 The two on the right have been subjected to the action of acetic 

 acid, by which they are rendered pale, and their nuclei much 

 more distinct. 



PLATE XV. 



ARTERIES, continued. 



FIG. I. Epithelial layer of the internal coat (from the 

 radial artery). 1, Nucleus ; 2, internuclear substance composed 

 of cells the outlines of which are not visible. 



FIG. II. Epithelial cells, isolated (from the radial artery). 



FIG. III. Fenestrated layer. 1, Amorphous material 

 through which the fibres of the subjacent coat are visible ; 2, 

 elastic fibres imbedded in the amorphous substance ; 3, openings 

 or fenestra, of various shapes and sizes ; 4, irregular line show- 

 ing where the layer has torn or ruptured ; 5, the subjacent layer 

 consisting of longitudinal elastic fibres (from the radial artery). 



FIG. IV. Longitudinal section of the primitive carotid 

 artery of a young subject (15 years of age) ; 1-2, internal 

 coat ; 2-3, middle coat ; 4, muscular fibres of the middle coat ; 

 5, their nuclei ; 6, network of elastic fibres ; 7, transverse sec- 

 tion of these same fibres. 



FIG. V. Same artery, dried like the preceding, and 

 treated by acetic acid. 1, Line of junction of its middle and 

 external coats. The latter (2) consists of a web of elastic fibres, 

 which run mostly parallel with the axis of the vessel, and are 

 crossed by connective fibres ; these have been rendered invisible 

 by the acetic acid. 



