Arteries The blood vessels and veins are built

ØArteries The blood vessels and veins are built up on the same plan, the wall of each being formed of three coats or layers: an inner epithelial and fibrous coat, a middle muscular coat and an outer connective tissue coat.

T. S. of Artery During examination of it the following can be noted: � The tunica intima, or the inner layer, consists of an endothelium of squamous cells followed by a wavy lamina of elastic connective tissue. � The tunica media, or middle layer, consists of circular unstriated muscle fibers held together by elastic and collagenous connective tissue fibers. This is the thickness layer in the wall of the artery. � The tunica adventitia, or outer layer, consists of areolar connective tissue which is especially rich in elastic fibers.

T. S. of a vein During examination of it the following can be noted: � The tunica intima, or the inner layer, consists of an endothelium of squamous cells but elastic connective tissue layer is poorly developed and may be totally absent. � The tunica media, or middle layer, consists of, as in artery, circular unstriated muscle fibers but this layer is relatively much thinner than that of the artery and contains more collagenous than elastic connective tissue fibers. � The tunica adventitia, or outer layer, is the thickest layer in the wall of the vein. It consists of areolar connective tissue containing mainly collagenous fibers.

The toad skin � It is mainly composed of two layers; an epidermis to the outside and dermis to the inside. � The epidermis, this is built out of a stratified squamous epithelium, that is, its cells are arranged in several layers or strata, one above the outer. The shape of the constituent cells of these layers is not uniform, for the cells of the basal are columnar, while those near the surface are flattened and scalelike, while those lying the surface are itself are dead and consistes of horny material. � Accordingly, the basal layer is called the malpighian layer, and the superficial layer called the horny layer.

� The dermis, this consists of a connective tissue differentiated into two distinct layers, the outer of which is build of an areolar connective tissue, hence called the spongy layer. While the inner layer is build up of a fibrous connective tissue, hence called the compact layer.