THE STRUCTURE OF THE MOTOR ORGANS. 117 



us for example the muscle Ss seen on the ventral side of the 

 shoulder-blade in Fig. 51. 



G-ross Structure of a Muscle. However the form of the 

 skeletal muscles and the arrangement of their tendons may 

 vary, the essential structure of all is the same. Each consists 

 of a proper striped muscular tissue, which is its essential 

 part, but which is supported by connective tissue, nourished 

 by blood-vessels and lymphatics, and has its activity governed 

 by nerves; so that a great variety of things go to form the 

 complete organ. 



A loose sheath of areolar connective tissue, called the peri- 

 mysium, envelops each muscle, and from this partitions run 

 in and subdivide the belly into bundles or fasciculi which 

 run from tendon to tendon, or for the whole length of the 

 muscle when it has 110 tendons. The coarseness or fineness 

 of butcher's meat depends upon the size of these primary 

 fasciculi, which differs in different muscles of the same ani- 

 rnal. These larger fasci- 

 culi are subdivided by finer 

 connective tissue, mem- 

 branes into smaller ones 

 (as shown in Fig. 55, which 

 represents a few primary 

 fasciculi of a muscle and 

 the secondary fasciculi into 

 which these are divided), FlG . 55 ._ A sma Ti bit of muscle composed 

 each of which consists of a of five g^^Bgvdfl^thne dKnwters^to 



Certain number Of micro- show the secondary fasciculi of which the 



primary are composed. 



scopic muscular fibres 



bound together by very fine connective tissue and enveloped 

 in a close network of blood-vessels. Where a muscle tapers 

 the fibres in the fasciculi become less numerous, and when a 

 tendon is formed disappear altogether, leaving little but the 

 connective tissue. 



Histology of Muscle. For the present we need only 

 concern ourselves with the muscular fibres. Each of these is 

 from eight to thirty-five millimetres ( to H inches) long, but 

 only from 0.034 to 0.055 mm. ( T fo to rhr inch ) in diameter 

 in its widest part and tapering to a blunt point at each end. 

 In cross-section the fibres are irregularly polygonal. In long 

 muscles with terminal tendons, no fibre runs the whole length 

 of a fasciculus, which may be a foot or more long, but the 



