The early professional players, including the very first CD-i player set (180/181/182) did not provide a standard CD tray like most CD-i players did, but they had a caddy loading system. This means that you need a seperate disc holder like you see above that holds the CD for you. CD's were inserted from the side (top) to keep it in place; the whole caddy was inserted in the CD-i player. The caddy's you see here were specifically for the CD-i 180 system.
The website Dutchaudioclassics describes it as following: "The clean mechanical design features of the CDI 180 make it extremely easy to operate. All the user has to do is insert the program disc into the player slot. Discs are pre-loaded into a twopart plastic caddy which slides easily into the player. This action automatically locates the disc in the playing position. The disc. held firmly in its mounting frame. is retained in this position and the now-empty box is with¬drawn.
The reverse action removes the disc after use. The box is inserted into the slot, as before, and the disc and its frame are relocated within the box (inside the player) ready for withdrawl. The box is now slid outwards with the disc already contained inside. This caddy facility avoids physical handling of the media and provides a practical, robust and compact storage element."
[Thanks, Marcels TV Museum& dutchaudioclassics]