£ 122 j v 
the will, and thofe which do not, one might expert 
them equally frequent on the nerves of the limbs, 
as at the rife and on the courle of the inter cojl ah , 
where they are numerous, large and conftant : on 
the nerves fent to the fenfory organs , and- on the phre- 
netic as well as the lenticular ganglion from which the 
Iris is provided with nerves. In a word the folici- 
tude, fo to exprefs myfelf, and the conftancy with 
which all parts whofe motions are involuntary are 
provided with nerves furnifhed and befet with gan- 
glions ; and the great fcarcity and rarity of them on 
nerves detached to mufcles fubjed to our volitions, 
and the total want of them on the fenfory nerves, 
fufficiently befpeaks their general diftindion and ufe, 
notwithstanding a few feeming exceptions. I fay 
feeming, becaule fome that are ailedged as exceptions 
are not permanently and conftantly found. To af- 
certain the ufe and importance of any part of animal 
jftrudure, we ought to be certain that it is conftantly 
found in that fituation ; if, on the contrary, it be only 
accidentally feen, and not perpetually, we can nei- 
ther a Sign any important ufe to it, or draw any im- 
portant dodrine from it, and have great reafon to 
fufped; it to be rather fome morbid phenomenon 
than otherwife. Now this is the cafe with refped 
to the ganglia defcribed by Mekelius as leated on 
twigs of the fecond and third branches of the fifth 
pair of nerves ; betwixt which and other ganglions 
Baron Haller makes a very cficntial diftindion, par- 
ticularly the ganglion ophthalmicum , which he fays is 
conftant and perpetual, whereas thefe beforemention- 
ed 
