on the human urethra. 
189 
means equally so in different instances. This has no regular 
boundary, and appears to be formed simply by the elastic 
plates being wanting. These plates, from their extreme 
elasticity, are with difficulty examined ; but as it appeared 
that their structure is the subject respecting which physiolo- 
gists are not agreed, Mr. Bauer spared no pains, and exerted 
his ingenuity in putting them to the test of different modes 
of examination on the field of the microscope, and is per- 
fectly satisfied that they are what he has represented them to 
be ; namely, simple thin membranous elastic plates, not made 
up of more than one layer, not having a cavity between them, 
nor in any way forming regular cavities, but having irre- 
gular interstices : they vary in size considerably in dif- 
ferent parts of the same body. It is into these interstices 
that the blood is occasionally received from the termination 
of the small arteries which are every where branching upon, 
and supported by, the elastic plates of which the trellis work 
is composed; as in PI. XVIII, Fig. x. PI. XIX, Fig. 1. 
PI. XX, Fig. 1. 
The circulation of the blood in these parts being different at 
different times, is a most beautiful illustration of the fact, which 
upon a former occasion I communicated to the Society; namely, 
the great influence the nerves have upon the action of the 
smaller arteries, as well as on their larger trunks. When the 
nerves that supply the corpora cavernosa and corpus spongio- 
sum, (and they are very numerous,) are not affected by the 
state of mind of the individual, the blood is not carried into this 
trellis work, but returns by the veins, as in other parts of the 
body ; but when the mind receives such impressions as excite 
these nerves, the smaller arteries have their action so much 
Cc 
MDCCCXX. 
