tlNSTRIPEt) MUSCULAR TISSUE. 65 



taut to observe that in the frog, and also in early foetal 

 development of mammals, the nuclei are imbedded in the 

 middle of the striated contractile substance. The fibres of 

 the heart have no sarcolemma. 



31. Unstriped Muscular Tissue is often arranged in 

 bands of indefinite length like the striped fibres ; but even 

 when this is the case, it consists of a series of elongated fusi- 

 form corpuscles varying usually from ^o" to ^^ of an inch 

 in length, and known as fibre-cells, although possessing no 

 proper cell-wall. These fibre-cells are flat, with long taper- 

 ing extremities, an elliptic or rod-like nucleus in the middle, 

 and at each end of the nucleus usually a few granules. They 

 are of dense consistence, and adhere one to another tena- 

 ciously by means of a material acted on by nitric acid. 



Fig. 31. FIBRE-CELLS OF UNSTRIPED FIBRE. 



32. New muscular fibres of both the striped and unstriped 

 variety, would appear to be capable of being developed from 

 connective-tissue-corpuscles. In both varieties the connec- 

 tion with the nervous system is effected by filaments of 

 nerves entering the interior of the fibre ; in striped fibres the 

 filaments end in swellings or expansions in or on the striated 

 substance, and in unstriped fibres certain observers trace 

 them to the nuclei of the fibre-cells. 



33. Muscular substance consists in greater part of muscle* 

 fibrin, a description of albuminoid material which, in the form 

 in which it is found after death, is termed syntonin, and is 

 distinguished from other varieties of fibrin by being soluble 

 in dilute hydrochloric acid. It would appear, however, that 

 during life the muscle-fibrin is in a fluid condition, and differs 

 from the syntonin found after death ; and it has, therefore, 

 been- distinguished as myosin. That a slight decomposition 

 sets in soon after death, seems certain from the circumstance 

 that dead muscle has an acid reaction, whereas muscle which 



