450 MOVEMENTS. 



It has been demonstrated by minute dissection that all 

 of the red, or voluntary muscles are made up of a great 

 number of microscopic fibres, known as the primitive mus- 

 cular fasciculi. These are called red, striated, or voluntary 

 fibres, or the fibres of animal life. Their structure is com- 

 plex, and they may be subdivided longitudinally into fibril- 

 lae, and transversely into disks, so that it is somewhat 

 doubtful as to what is, strictly speaking, the ultimate ana- 

 tomical element of the muscular tissue. 



A primitive muscular fasciculus runs the entire length 

 of the muscle, and is enclosed in its own sheath, without 

 branching or inosculation. This sheath contains the true 

 muscular substance only, and is not penetrated by blood- 

 vessels, nerves, or lymphatics. If we view with the micro- 

 scope a thin transverse section of a muscle, the divided ends 

 of the fibres will present an irregularly polygonal form with 

 rounded corners. They seem to be cylindrical, however, 

 when viewed in their length and isolated. Their color by 

 transmitted light is a delicate amber, resembling somewhat 

 the color of the blood-corpuscles. 



The primitive fasciculi vary very much in size in dif- 

 ferent individuals, and in the same individual under different 

 conditions and in different muscles. As a rule they are 

 smaller in young persons and in females than in adult males. 

 They are comparatively small in persons of slight muscular 

 development. In persons of great muscular vigor, or when 

 the general muscular system or particular muscles have been 

 increased in size and power by exercise, the fasciculi are 

 relatively larger. It is probable that the physiological in- 

 crease in the size of a muscle from exercise is due to an 

 increase in the size of the preexisting fasciculi, and not to 

 the formation of any new elements. In young persons the 

 fasciculi are from 17 1 00 to 12 * 00 of an inch in diameter. In 

 the adult they measure from ^-J-0- to -^^ of an inch. 1 



The appearance of the primitive muscular fasciculi 



1 LITTRE ET ROBIN, Dictionnaire de Medecine, Paris, 1865, Article, Musculaire. 



