The arrow points to the urethral orifice. The other two lines in the vaginal mucosa are folds in the tissue. Some bitches have a prominant mound of raised tissue around the urethral orifice. Gently probe the urethral orifice with the urinary catheter to confirm that it is the urethral orifice and not a fold of tissue. This is a Foley catheter being placed throughthe otoscope.
Magnification makes it easier to see the urethral orifice.
You can use a stainless steel catheter as a stylet for a Foley catheter. The steel catheter is fitted into the eye of the Foley and the two are passed together into the bladder. Foley catheters as the steel catheter will not fit in the eyehole of smaller Foleys. Lubrication of the metal catheter before it is inserted into the eyehole makes both insertion and removal of the metal catheter easier. The Foley bulb is inflated and the metal catheter is removed.