Four represents Enclosure, Completion, Foundation. It is a symbol of Earth, the 4th element. Fours are here to build a firm foundation, to labor with concentration and secure the right to work out their patterns of freedom from any obstacles-poverty, heartache and failure.
Epithelial tissue comprises one of the four basic tissue types. The others are connective tissue (support cells, immune cells, blood cells), muscle tissue (contractile cells), and nervous tissue. Organs represent various combinations of these four basic tissue types, which thus comprise the entire body.
The epithelium continues the pseudostratified characteristics seen in the Olfactory epithelium. It is also ciliated and contains goblet cells. The connective tissue under the epithelium is called the adventitia. In this connective tissue are numerous seromucous (mixed) glands, as well as blood vessels and nerves. These are called tracheal glands. Identify the serous and mucous cells in the glands on your section and also on this photograph (to the left).