282 



MANUAL OF HISTOLOGY. 



situation is generally at an equal distance from both ends and in the axis 

 of the cell, as may be best seen in transverse sections of previously dried 

 muscle (*) ; from which, also, we may convince ourselves of the cylin- 

 drical form of most of the fibres. In 

 most cases the nucleus is only single ; 

 but two, three, or even four, may 

 occur in one cell (Remdk, Koelliker, 

 G. Schwalbe), a circumstance of great 

 importance in tracing the relationship 

 , , - nx of these to striated muscle fibres. 



F 111 llVWV It is only very lately that, by the 



i III l\ tX\\\\%. a id of more advanced technical know- 



ledge, we have been enabled to render 

 visible in many nuclei, single or mul- 

 tiple (1-4), granules of round form and 

 glittering appearance, which have pro- 

 bably the significance of nucleoli. 

 Their diameter is 0-0009-0-0002 mm. 

 (Hessling, Frankerihauser, Arnold, 

 Schwalbe}. 



Under the polarising microscope 

 the contractile fibre-cell is found to 

 \* \\ i re 1 1^P&~ ^ e d ou kl e refracting and positive to 



\ \ f a flB^ the axis ( Valmtin )- 



^ \\ " )' * But though this cell appear thus 



singular in a state of maturity, it 

 bears in the embryonic body a less 

 striking character; the nucleus is then 

 round and vesicular (a, &). Whether 

 this original constitution may not per- 

 sist in many parts of the body is a 

 question incapable at present of being 

 answered. Besides this, it is impossible 

 to indicate any very certain features of 

 distinction between the fusiform cells 

 of connective-tissue, which are like- 

 wise endowed with vital contractility, 

 and the elements of smooth muscle. 

 The many controversies which have 

 taken place in the last few years as to 

 whether we are to admit the presence 

 of contractile muscle cells in this part and that, or no, must be judged 

 accordingly. 



On the other hand, the singly nucleated contractile fibre-cells may 

 acquire striated contents, and thus approach nearer to the elements of 

 voluntary muscle. 



Among such may be reckoned the elements of the muscle of the heart 

 of lower vertebrates ( Weismann), of the bulbus aortae of the salamander 

 and proteus (Leydig)-, but probably not the fibres situated under the 

 endocardium of the ruminants, of pigs and horses, bearing the name of 

 the fibres of Purkinje. 



Smooth unstriped muscle is to be found throughout the whole diges- 

 tive tract, from the inferior end of the oesophagus down nearly to the 



Fig. 273. Smooth muscle fibres from the 

 human being and other mammals, a, a for- 

 mative cell from the neighbourhood of the 

 stomach of a foetal pig ten inches long ; ft, 

 another more developed ; c-g, various forms 

 of contractile cells from the human body ; 

 A, one of the latter, containing fat granules ; 

 <, a bundle of smooth muscle fibres;*, a 

 transverse section through one of these 

 from the aorta of the ox, with several nuclei 

 In the plane of the cut. 



