I am not able to identify with certainty the item listed as "Tr" in the attached file "Photo.pdf".Picture: Photo_00 and the elements "Tg".
It is a cross section of a mouse embryo, stained with H&E, the diameter of the sample is about 8 mm, low magnification x40.
The other attached pictures are particulars of the item "Tr".
Photo_01, low magnification x100
Photo_02/03/04, medium magnification x440.
Despite the apparent absence of cartilage tissue I'd try to suppose as trachea for "Tr" and "Tg" like thyroid glands.
Thank you for your help and suggestions,
With my Best Regards,
Massimo Tosi