For a start, let's understand in short, what the ventricular system is?
The ventricular system is a set of four interconnected cavities called ventricles (see diagram) inside the brain, where the cerebro-spinal fluid (CSF) is produced. The ventricular system is continuous with the central canal of the spinal cord, from the fourth ventricle (see diagram) allowing for the flow of CSF to circulate.

I have also uploaded a quirky diagram that shows what the different parts are.
You can read more about this unique and clinically significant anatomical part on this informative page.

After fusing, sharpening and analyzing the boundaries & structure of the extracted ventricles from the repository, I have also modeled a stand for holding upright the ventricular system so you can showcase it where you desire. This can be printed as an educational model to teach students about how the ventricular volumes are connected.

This unique addition to Thingiverse has been made possible because of medical data sets available online that have further been post-processed using mesh manipulation tools.

Consider supporting my designs on Patreon, here: https://www.patreon.com/akshayd21
Thank You!

Diagram Image Source
Model Repository Source

Notes:
Model Update v1.2 [07/28/2017] Thingiverse user Debra Summers noticed separate shells on the model while slicing. The error is fixed and a revised and renamed model has been updated in the files section.('Ventricles_updated')