122 



THE HUMAN BODY. 



Somewhat similar bodies (Golgi's tendon-organs] are found 

 in the tendons and are also richly supplied with nerve-fibres. 

 In histological structure the tendon-organs and the muscle- 

 spindles appear to be allied to Pacinian bodies (Chap. XXXV). 

 Structure of the Unstriped Muscles. Of these the 

 muscular coat of the stomach (Fig. 59) is a good example. 



FIG. 59. The muscular coat of the stomach. 



They have no definite tendons, but form expanded membranes 

 surrounding cavities, so that they have no 

 definite origin or insertion. Like the skel- 

 etal muscles they consist of proper contractile 

 elements, with accessory connective tissue, 

 blood-vessels and nerves. Their fibres, how- 

 ever, have a very different microscopic struc- 

 ture. They present a slightly marked longi- 

 tudinal but no cross striation and are made 

 up of elongated cells (Fig. 60), bound to- 

 gether by a small quantity of cementing 

 material. The cells vary considerably in 

 size, but on the average are about ^ mm. 

 ({T^g- inch) in 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 with 

 one or two nucleoli. These cells have the 

 Unstriped power of shortening in the direction of their 

 muscle-ceils. long axes, and so of diminishing the capacity 



of the cavities in the walls of which they lie. 



