. Chordate morphology. Morphology (Animals); Chordata. 8 The Skin and its Derivatives The skin of the vertebrate consists of two layers, an outer epidermis of ectodermal origin and an inner dermis of meso- dermal origin. Each of the layers, in contrast to those of the invertebrates, is formed of several kinds of cells and several forms of the same kind of cell (Figures 8-1, 8-2). Both parts may be involved in the skin derivatives, which include teeth, scales, bony plates, keratinized scales, nails, feathers, hair, several types of glands (including the mammary glands), and many sensory structu
. Chordate morphology. Morphology (Animals); Chordata. 8 The Skin and its Derivatives The skin of the vertebrate consists of two layers, an outer epidermis of ectodermal origin and an inner dermis of meso- dermal origin. Each of the layers, in contrast to those of the invertebrates, is formed of several kinds of cells and several forms of the same kind of cell (Figures 8-1, 8-2). Both parts may be involved in the skin derivatives, which include teeth, scales, bony plates, keratinized scales, nails, feathers, hair, several types of glands (including the mammary glands), and many sensory structures. The latter, with one exception (prototrichs), will be described as parts of the nervous system. SKIN The epidermis of the higher forms is stratified into several layers of cells. Essentially one type of cell is envolved in the epidermis, and it undergoes several changes in form as it moves from the base of the epidermis to the surface. This outer layer of the skin is generally without a blood supply and without nerves, although sensory cells, are found here in the lower forms. In a few instances, nerve endings may penetrate the epidermis. Capillaries lie close to the basal layer of the epidermis, the Malpighian layer or stratum germinativum, from which the cells of the epidermis are hair sweat gland pore interpapillory peg stratum cornium stratum lucidum stratum granulosum .stratum spinosum stratum germinativum. dermal papilla sebaceous gland sweat gland Figure 8-1. A steriodiagram of human skin. The outer layer of epidermis is several times thicker than it should be in order to show its layering. The hair follicle is proportionally reduced in order to keep the follicle within the limits of the diogrom; the diameter of the hair is actually somewhat greater than the thickness of the epidermis (see Figure 8-3). 217. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these i
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