CHAPTER III 

 INTEGUMENT 



Integument or skin is the covering of the body. Its form, 

 thickness and physical consistency, in all cases, provide some 

 degree of protection from mechanical injury. Combined with 

 this purely passive function of the skin is a nervous function 

 maintained by sensory-nerve endings located just below the 

 surface of the body. Since the entire nervous system evolved 

 from the primitive integument or ectoderm, the nervous function 

 of the skin is one of its primary functions. Respiration, the 

 absorption of gaseous oxygen and the evolution of carbon dioxide, 

 is another primary function of the integument and one that 

 persists in the integument of many animals. The protective 

 function of the integument, provided by its toughness or texture, 

 is further extended in some cases by the presence of glands 

 capable of secreting poisonous, slimy, or malodorous substances. 

 Sebaceous glands, producing oil, and sudoriparous glands, pro- 

 ducing sweat, are found in the skin of some animals. 



Integument of the Frog. — The outer layer of the integument 

 of the frog is known as the epidermis. Beneath this is the 

 corium or dermis. These two layers occur in the skin of all 

 vertebrates. 



Epidermis. — The epidermis consists of two regions: the 

 stratum corneum at the surface, and the stratum germinativum 

 below, both of which are epithelial in structure (Fig. 19). An 

 epithelium may be defined as one or more layers of cells, com- 

 pactly arranged, covering an external or internal surface of the 

 body of an animal or derived from such a surface. The stratum 

 corneum, an example of a simple squamous epithelium, is com- 

 posed of broad flattened cells of a horny texture, and serves 

 as the outermost protecting layer of the skin. From time to 

 time this layer is shed as a whole, a process known as molting or 

 ecdysis. The stratum germinativum is composed of several 

 layers of cells, forming a stratified epithelium. The innermost or 



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