ORGANIC STRUCTURE : MORPHOLOGICAL 49 



many, of the cells in a muscle that initiate the tension of the 

 latter (see Nos. 5-8, Fig. 14). 



Nervous tissue. Everyw^here in ganglionic centres and nerves 

 the elements are nerve-cells (see Section 41). Nerve-cells, or 

 neurones, in various modifications, constitute the central and 

 peripheral parts. Everywhere nerve fibres and nerve-cells are 

 bound together by connective tissue (see No. 3, Fig. 13). 



Glandular and metabolic tissue. The units are cells of various 

 forms (see Nos. 3-6, Fig. 12). 



Vascular tissue. Such is that making up the tubes which carry 

 blood, lymph, etc. Arteries, veins and capillaries are really 



Fig. 15. 



I, Connective tissue corpuscles ; 2, areolar connective tissue ; 3, fibrous connective tissue ; 

 4, a squamous epithelium ; 5, a cubical-celled epithelium ; 6, a ciliated epithelium ; 7, a 

 " pavement " epithelium ; 8, squamous epithelial cells forming the wall of a blood capillary 

 vessel ; 9, an epidermis. 



organs. Thus an artery has a complex wall in which are both 

 muscles and nerves. But it is convenient to think about connect- 

 ive tissue as being modified to form the small veins and capillaries 

 as w^ell as the obscure channels through which blood and other 

 circulating fluids pass in the lower animals and, in a sense, there is 

 a tubular or vascular kind of connective tissue. (No. 8 of Fig. 15.) 



Epithelial tissue. This consists of layers of cells that form 

 sheets. These epithelia, or sheets, line internal cavities, the body 

 cavity, the mouth, the bladder, heart, arteries and veins, etc. 

 The epithelia may be glandular (Fig. 15). 



Epidermal tissue (No. 9 of Fig. 15). The external layers of 

 integument comprise this. 



Connective tissue (Fig. 15). This consists of the ubiquitous 



