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I was looking at some photos today and came across this one:

enter image description here

I noticed four little things in between the horizontal and vertical stabilizer. Could somebody explain me what those are?

Thank you in advance.

Image source

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From what I see, they are not antennae. I might guess that they are static-relievers but I may be wrong. – SMS von der Tann Jan 26 at 20:58
We also have this question which is very similar aviation.stackexchange.com/questions/24427/… – SMS von der Tann Jan 26 at 21:17
do you mean the metal plates over the fuselage? – Trebia Project. Jan 26 at 21:23
Personally, looking at that picture I would asked about tube like formation on the back. – Burhan Khalid Jan 27 at 7:26
What are those "tube-like" structures ahead of the vortex generators ? – Jorge Aldo Jan 27 at 7:32

The objects are vortex generators. In general, vortex generators serve to introduce turbulence which helps to prevent flow separation. More information here:

This was to reduce elevator and elevator tab vibration during flight to increase their hinge bearing service life.

As mentioned on the site, you can see these on any 737 version from the original -100/-200 up through the NG. Better image from same site:

View of aft body vortex generators

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