86 THE HUMAN BODY 



contains many nuclei and lies close under the sarcolcmma, its 

 deeper side being in immediate contact and possibly continuous 

 with the striated contents. These nerve-fibers are motor or con- 

 cerned in exciting a contraction of the muscle-fiber. 

 Other nerve-fibers are connected with very peculiar 

 bodies found scattered throughout the muscle, but 

 especially numerous near the tendons. They are 

 usually of a size just visible to the unaided eye and 

 from their form have been named muscle-spindles. 

 They are doubtless sensory in function. Somewhat 

 similar bodies (Golgi's tendon-organs) are found in the 

 tendons and are also richly supplied with nerve- 

 fibers. 



Structure of the Smooth Muscles. Of these the 

 muscular coat of the stomach (Fig. 43) is a good ex- 

 ample. They have no definite tendons, but form 

 expanded membranes surrounding cavities, so that 

 they have no definite origin or insertion. Like the 

 skeletal muscles they consist of proper contractile 

 elements, with accessory connective tissue, blood- 

 vessels, and nerves. Their fibers, however, have a 

 very different microscopic structure. They present 

 a slightly marked longitudinal but -no cross striation 

 and are made up of elongated cells (Fig. 44), bound 

 together by a small quantity of cementing material. 

 The cells vary considerably in size, but on the aver- 

 age are about yj mm - (STTF in-) i n length. Each is 

 flattened in one plane, tapers off at each end, and 

 possesses a very thin enveloping membrane; in its 

 interior lies an elongated nucleus. These cells 

 FIG. 44. have the power of shortening in the direction of 



mulcle ds ?eUs ^^ T ^ ong axeSj anc * so ^ diminishing the capacity 

 from human of the cavities in the walls of which they lie. 



small intestine. ~ ,. _, 



Cardiac Muscular Tissue. This consists of nu- 

 cleated branched cells which unite to form a network, in the in- 

 terstices of which blood-capillaries and nerve-fibers run. The cells 

 present transverse striations, but not so distinct as those of the 

 skeletal muscles, and are said to have no sarcolemma (Fig. 45). 

 Ciliated Cells. As the growing Body develops from its prim- 



