20 



PHYSIOLOGY OF FARM ANIMALS 



[CH. 



contains the nucleus. Adipose tissue is fouiul mainly just 

 beneath the skin, and in other places where it serves as a j^ack- 

 ing, holding the organs in position and protecting them from 

 injury. It helps to give the limbs their characteristic contour. 

 It provides a store of nutriment for the bodily requirements, 

 besides acting as a non-conductive layer under the skin, and so 

 helping to retain the bodily heat. In fat animals adipose tissue 

 occurs in great quantity in the abdominal cavity, especially in 

 the region of the kidneys, as well as between the various 

 muscles; sometimes also the muscles are themselves penetrated 

 by fat, the flesh becoming marbled in appearance. 



(3) Muscular Tissues. 



Muscular tissue consists mainly of fibres in which all the 

 primitive functions of the cell have become subservient to the 



function of contractility. There are 

 three kinds of muscular tissues, which 

 differ from one another both in their 

 histological structure and in the func- 

 tions which they perform. 



In voluntary or striated muscle the 

 fibres are long and cylindrical with 

 characteristic cross striping, consisting 

 of alternate dark and light bands. 

 Each fibre has an elastic sheath, 

 called the sarcolemma, which insu- 

 lates the cells from one another and 

 assists in forming the attachment of 

 the muscle to the bone. In addition 

 to the sarcolemma and striated sub- 

 stance, a muscle fibre has also a 

 number of oval nuclei generallj^ 

 associated with a little inidifferenti- 

 ated cell protoplasm. This proto- 

 plasm, together with the interstitial 

 substance between the elements com- 

 posing the fibre, is the remains of the 

 protoplasm of the cells which originally gave rise to the muscle 

 fibres. Striated muscles are attached to the bones of the body 

 and are under the control of the will ; hence they are also 



Fig. 14. Striated muscle show- 

 ing capillary vessels (from 

 Schafer). 



