522 



THE CELL AND MAMMALIAN HISTOLOGY 



Red muscle fibres have more sarcoplasm and fewer fibrils, the 

 nuclei are more scattered and the cross striations are less distinct, 

 than in white muscle fibres. The two are generally found mixed 

 in the muscle, and the red fibres have a slower and more sustained 

 contraction. Their colour is due to myohaemoglobin, which, like 

 the related hcumoglobin of the blood, can hold oxygen and give it 

 up when it is needed. 



Fig. 407. — Diagrammatic representation of a motor end-plate m a muscle. — From 

 Le Gros Clark, The Tissues of the Body, 3rd edition, 1952. Clarendon Press, 



Oxford. After Gutmann and Young. 



m., myelin sheath ; n., neurilemma ; s.n., nucleus of Schwann cell ; s.a.. sarcolemma. 



Muscles make up the flesh or meat of the body. They are well 

 suppHed with blood vessels, which do not penetrate the sarco- 

 lemma. Motor nerve fibres do pierce this sheath, and end in 



Fig. 408. — Isolated plain muscle fibres, showing nuclei. — From Le Gros Clark, 

 The Tissues of the Body, 3rd edition, 1952. Clarendon Press, Oxford. 



branched motor end organs in the sarcoplasm, where they 

 probably induce contraction by the liberation of a chemical 

 substance (Fig. 407). A smaller number of sensory nerve fibres 

 end in modified muscle fibres, the muscle spindles, which respond 

 to the stretching of the muscle. Muscle fibres are bound together 

 by areolar tissue into small bundles or fasciculi, and these again 

 into individual muscles. The toughness of meat depends largely 

 on the amount of the connective tissue and especially on the 

 proportion of white fibres which it contains. The connective tissue 



