260 



their course. These arteries it should be added, were taken from 

 bodies ranging in age from 10 to 60 years. As shown in Figures I and 

 II, these bundles do not encircle the whole artery. Seen in transverse 

 section, the artery may exhibit now one, now two, very rarely three 

 such bundles, sometimes situated in the more internal portion of the 

 media, sometimes in the more external portion. The individual 

 bundles rarely involve a quarter of the whole circumference. 



I may add further I have studied the artery that has the largest 

 bend in the body, namely, the aorta, and there have encountered 

 none of these oblique bundles. This would rather suggest that it is 

 not the mere fact of the artery being curved which favors the appear- 

 ance of these oblique fibres, as it is the liability of an artery to be 

 subjected to various grades of bending. 



I have endeavored so to mark certain of these arteries upon 

 removal from the body as to be able to determine later the relationship, 

 e. g., in the case of the popliteal, which was the deeper aspect tow^ards 

 the bone, which the more superficial: to determine that is, which 

 aspect of the artery had undergone stretching when the leg was bent 

 upon the thigh, which, on the contrary, had undergone compression. 

 Doing this I have to confess that so far I have been unable to determine 

 with any precision the particular site of these accessory bundles. 

 At the present time, therefore, I will not venture to make any state- 

 ment, or even suggestion regarding their distribution, further than 

 that they evidently occur in arteries subjected to fairly acute curva- 

 ture, and to the extent of my experience are absent elsewhere. I have, 

 for example, sought for oblique bundles in the immediate neighbor- 

 hood of important arterial branches, but have failed to come across 

 them. 



From these observations the following conclusions may, I think, 

 safely be drawn: 



1. When the course of an artery is straight, and it is not sub- 

 jected to bending, the muscle fibres of its media are circularlj^ dis- 

 posed. 



2. When the course of an artery is not straight, and when it is 

 subjected to bending of various grades, the circularly disposed fibres 

 of its media are reinforced by oblique or longitudinal bundles, the 

 oblique fibres occurring much more frequently than the longitudinal. 



3. These oblique and longitudinal fibres are to be found in the 

 middle coat in all periods of life. 



