232 PHYSIOLOGY AT THE FARM. 



Other lamella in the long bones are concentric with the 

 medullary canal, and again other lamellae are discovered in 

 different parts of the section. 



What were formerly termed bony corpuscles are now found 

 to be lacunae, or minute cavities, which communicate by trans- 

 verse minute passages termed " canaliculi/' 



The bones are plentifully supplied with blood, and even 

 nerves and lymphatics have been described. 



Muscular Fibre. The muscular tissue is the great agent in 

 the locomotions of the living body. It constitutes the flesh of 

 animals, in the large sense in which that word includes the 

 moving substance of birds, fishes, and other animals. The 

 muscular tissue is composed of fine fibres collected into dis- 

 tinct organs termed muscles. Such fibres are also arranged 

 round the sides of cavities and between the tunics of hollow 

 viscera, where these fibres form strata of greater or less 

 thickness. The property which distinguishes muscular fibres 

 is named contractility. The property bearing this name is 

 that by which a muscular fibre, under several known con- 

 ditions, shortens itself, and again becomes elongated when 

 the condition just before applied ceases. The ordinary con- 

 ditions under which a muscular fibre contracts are grouped 

 together under the name of stimuli. Even when a muscular 

 fibre contracts or shortens itself in obedience to the will, 

 the will is said to act as a stimulus to its contraction. 

 When the will acts, however, it is through a nerve, the 

 filaments of which reach the group of muscular fibres con- 

 stituting a muscle. The muscular fibres which contract in 

 obedience to the will, contract also under other stimuli, whether 

 applied directly to the nerve or to the muscular fibre. Never- 

 theless, owing to their property of obeying the will, they are 

 called voluntary muscular fibres. The muscular fibres that 

 cannot become obedient .to the will constitute a distinct class 



