1 8 Mr. Carlisle's Account of a peculiar Arrangement 
part of the abdominal aorta, and, in men, descend from thence 
to the testicles : they are usually but two in number, and are 
called the spermatic arteries. Through an extent of ten inches, 
by average computation, these vessels give off comparatively 
few lateral branches, so that they may be properly considered 
as the longest arterial cylinders in the body. The spermatic 
arteries supply the muscles called cremasters, which suspend 
the testicles, and the fibrils of the dartos, which corrugates the 
scrotum. The slow actions of these muscles, and their occa- 
sional long continuance in a contracted state, are sufficiently 
known. The next in resemblance are the intercostal arteries ; 
and lastly those of the diaphragm. Now the slowness of the 
muscular actions in respiration, and the occasional duration of 
arbitrary actions in these muscles, need only to be mentioned. 
Whether the peristaltic motions of the alimentary canal be in- 
fluenced by the circuitous course of some of the arteries, and 
their numerous junctions, I am unable to determine ; but these 
arteries are distributed differently, in those respects, from the 
arteries of ordinary muscles. 
The iris, in man, and in animals, is furnished with cylindrical 
arteries, which pierce the posterior part of the globe of the eye, 
and finally enter that muscle by a circuitous course.* The 
pupil of the eye contracts slowly, and is occasionally required 
to continue long in that state. 
The instance of an opposite mode of distribution, is to be 
found in the coronary arteries which supply the heart, a muscle 
whose actions are more rapid than those of any other; at the 
same time it is observable, that the coronary arteries are more 
* Vide Zinn. Descriptio anatomica Oculi bumani, Plate 3, Fig. 2, bb, and 
Fig. l, mn. 
