THE OSSEOUS TISSUE. 



47 



animal matter, the two being everywhere intimately blended; for the 

 former may be removed by acids, and the latter by burning, without 

 destroying the shape of the bone. In bone softened by acid, a fibrous 



Fig. 22. 



Fig. 22. (Sharpey.) a, cross-slice of the ulna, one of the bones of the forearm, showing the cavity for the 

 marrow in the centre, and the pores in the surrounding bone, b, the dark piece of a, highly magnified, 

 showing the canals of Havers, and the laminated structure of the surrounding solid bone, a, natural size; 

 6. magnified 12 diameters. 



structure can be shown in the laminae. Healthy bone is a very strong 

 material : it is somewhat elastic ; and the hollows in its substance, 

 besides facilitating its nutrition, make it mechanically better fitted for 

 its purposes, by spreading out a given weight of substance into more 

 space, and making it proportionally more resistant. 



Fig. 23. 



Fig. 23. (Sharpey.) A very fine section of bone, showing two of the canals of Havers, with the surround- 

 ing bony laminae, between which are the little bodies called the corpuscles or lacunas of bone, with fine 

 lines radiating from them, called the canaliculi of bone. This section is supposed to be examined on a 

 black ground, so that the hollow parts are dark, and the solid parts white. Magnified 90 diameters. 



Muscular tissue. There are two kinds of muscular tissue in the 

 body, one consisting of plain or unstriped muscular fibres, and the 

 other of striped or striated muscular fibres. The former kind is found 

 in the walls of the alimentary canal, in the sides of the air-tubes and 

 ducts of glands, in the skin, and in the coats of the bloodvessels and 

 larger absorbent vessels. The latter kind forms the substance of the 

 muscles of the body ; but the substance of the heart also consists of an 

 imperfectly characterized striated muscular tissue. 



The plain or unstriped muscular fibres are soft, pale, smooth, and 

 roundish or slightly flattened, Fig. 24, a. Their substance is indis- 



