in] of the New Physics. 71 



written by a Dane, Nicolas Stensen, better known perhaps by 

 his Latin name of Steno, to whom I have already referred and 

 of whom I will venture to say something more in detail in a 

 succeeding lecture. Stensen had used the microscope and had 

 been led to the following conception of the structure of a 

 muscle. 



According to him a muscle is essentially a collection of 

 motor fibres. Each motor fibre (fibra motrix), itself a complex 

 of most minute fibrils, arranged lengthways, has a middle 

 part, which differs in consistency, thickness and colour from 

 each of the ends. The several motor fibres are bound together 

 by the continuous transverse fibrillae of the proper membrane 

 of the muscle. The middle parts of the motor fibres, wrapped 

 round by the membranous fibrillse, constitute together the 

 fleshy part of the muscle, which soft, broad and thick differs 

 in colour in different animals, being reddish or pale or even 

 whitish ; in the leg of the rabbit you will find some muscles 

 red and others pale. The end parts of the motor fibres, which 

 are always white, thin, and tough, constitute together the 

 tendons. It is the fleshy parts of the motor fibres and these 

 alone which contract, and in doing so become shorter, harder, 

 and corrugated on the surface ; the tendinous parts remain 

 unchanged. 



It will be seen that Stensen had come very near to a 

 true conception of the structure of muscle. What he called 

 a ' motor fibre ' we now call a ' fasciculus,' his ■ most minute 

 fibril' is our 'elementary fibre,' and we speak of his 'proper 

 membrane ' with its transverse fibrillae as ' the connective tissue 

 framework.' Stensen too like Borelli was full of the new 

 spirit of the mechanical philosophy of the day ; and the greater 

 part of the work of which I am speaking is taken up with 

 elaborate mathematical mechanical expositions. In a muscle, 

 says Stensen, the middle fleshy part is an oblique angled 

 parallelepiped, and the tendon at each end is a tetragonal 

 prism ; and he develops at length the geometrical consequences 

 of this conception. 



Borelli was acquainted with Stensen's work, he accepts his 

 exposition of the structure of muscle, and speaks of muscular 



