cell wall
The stratum corneum is the tough outer layer of the skin.
the seed coat
There are a couple of definitions of the word "rind." Rind can refer to the stripping of bark off a tree, or rind can be used to describe the outer layer of something, with the layer being tough.
The cell wall is a tough, yet flexible layer surrounding certain types of cells. It functions as a structural support and protection to prevent water from entering.
The tough outer covering of Euglena, and Paramecium is called the Pellicle
The stratum corneum is the tough outer layer of the skin.
The cell wall
Endoskeleton
The tough white coating of the eye is called the sclera.
anulus fibrosus
a tough outer layer of the cell, which contains cellulose to provide strength and support to the plant.
This is called bark.
the dura
the seed coat
The epidermis is tough because it is a dense layer of skin cells held together by keratin, which is a hard protein. The epidermis is the outer layer of the skin.
The outer-most layer of a plant cell is the cell wall. This is mainly composed of cellulose, hemicellulose and pectin. The cell wall is a rigid structure that plays an important role in support, and is not found in animal cells.
connectiveThe outer layer of a blood vessel (artery or vein) is called the tunica externa or tunica adventitia.See http://training.seer.cancer.gov/module_anatomy/unit7_3_cardvasc_blood1_classification.htmlpericardium is the layer of the blood vessel that is made of tough connective tissue.