CHAP. XXVIII.] THE MIDDLE COAT OF ARTERIES.. 



interlacement which is represented in fig. 187. This 

 disposition of the fibres may be particularly well seen 

 on thin sections made from the dried aorta of the ox, 

 and afterwards moistened with acetic acid. It is also 

 sufficiently obvious in the aorta of the human subject ; 

 but the fibres are all very much smaller, nearly one- 

 half the size of those of the ox, and the penniform 

 subdivision is not so distinct. 



Muscular Fibres. Interposed between the layers 

 of penniform fibres we find some of the wavy white 



Fig. 189. 



319 



__ 

 ~~ ~ 



A portion of the circular fibrous coat, showing the penniform branching 

 of the large rods of elastic fibrous tissue, each large rod giving origin to 

 multitudes of small interlacing fibres. Magnified 200 diameters. 



fibrous tissue also arranged in a circular form ; and 

 intermingled with this are some transverse fibres of 

 unstriped muscle, with oval nuclei, whose long axes 

 are at right angles to the arterial canal (fig. 191) . 



Fig. 190. 



Fig. 183. 



A single bar or penniform fibre from the circular fibrous tunic of the 

 aorta of the ox, the small fibres having been broken off. Mag. 400 diam. 



These do not seem to form a single uniform layer, 

 but are disposed probably on different planes (some- 

 what like the fibres of the dartos in the areolar tissue 

 of the scrotum) among the fibres of the circular fibrous 

 coat, and follow the same direction. They are best 



A section of the whole thickness of the arteiy, to show the relative extent of 

 the portions of it>; walls shown in the preceding fig. Magnified 40 diameters. 



. The coarsely iibrous portion of the longitudinal fibrous tunic; b. the longitudinal fibrous 

 tunic and a portion of the circular fibrous tunic ; c. the entire thickness of the artery. 



