. Chordate morphology. Morphology (Animals); Chordata. -cuticle secretion of outer layer (striated) m . tri — pigment granules epidermal (sensory and secretory cells) outer fibrous layers (at right angles) middle gelatinous layer with ^cutaneous canal (lined) dermal cell inner fibrous layer inner cellular layer Figure 8-2. Section through the skin of omphioxus. derived. New generations of cells are delaminated from this layer and move outward with each subsequent generation until they reach the surface and are sloughed off. The dermis is a fibroelastic connective tissue in which the multicellu
. Chordate morphology. Morphology (Animals); Chordata. -cuticle secretion of outer layer (striated) m . tri — pigment granules epidermal (sensory and secretory cells) outer fibrous layers (at right angles) middle gelatinous layer with ^cutaneous canal (lined) dermal cell inner fibrous layer inner cellular layer Figure 8-2. Section through the skin of omphioxus. derived. New generations of cells are delaminated from this layer and move outward with each subsequent generation until they reach the surface and are sloughed off. The dermis is a fibroelastic connective tissue in which the multicellular glands of the epidermis are embedded. This layer of the skin is formed around interlaced collagenous and elastic fibers in a gelatinous matrix. The outer layer is usually the more densely fibrous, while deeper parts are more open. This tissue may become bony or filled with fat cells. Its surface capillary net is of importance in the maintenance of the epidermis and, in some animals, for respiration. The skin functions in a number of ways. It forms an enve- lope for the body, and a surface of contact with the environ- ment. It protects the body from abrasion, presents a barrier to disease, acts as a barrier to free exchange of material with the environment (mainly water), and becomes involved in body temperature control with the production of feathers and fur. Mammals The epidermis of the mammal is covered externally by the stratum corneum, a layer of flattened, keratinized, dead cells. The thickness of this cornified layer varies according to the amount of wear to which the skin is exposed. Thick or thin, this layer functions as a protection against drying and is lubricated by sweat and by sebaceous (oil secreting) glands. In the epidermis of man there is a sequence of cell layers. This sequence is as follows: stratum germinati- vum at the base, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. The cells of the stratum germinativum are generally
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