48 MUSCLE. 



be teased into separate fibres for any length, as it tends 

 to break off short. (L) Note the branching nature of 

 the fibres. (H] The well-marked cross and faint longitudinal 

 striation, the nucleus in the substance of the fibre, and the 

 abrupt transverse cleavage into short segments. These segments 

 are the tissue units. 



Cardiac muscle. L.S. Man or sheep, (p. 2 (d), s. 22 & 24, c. P., 

 m. B.) (//) Note the transverse cement lines, stained, which 

 define the segments. Each segment possesses a nucleus. In thin 

 sections the latter may often be cut away and a segment may 

 thus appear to be devoid of a nucleus. 



The same. T.S. Observe the oval and often irregular 

 outlines and difference in size, the central nucleus and the 

 separation of the substance of the fibre into sarcoplasm and 

 muscle fibrils (forming sarcostyles, bundles of fibrils). 



Cardiac musde. Dog. L.S. Coloured injection (p. 2 (d}^ 

 17 or 22, c. P., m. B.) (L) and (II). There is a rich dis- 

 tribution of capillaries parallel to the fibres with intercom- 

 munications. The arteries and veins give off their capillary 

 branches in fan-shaped clusters. 



12 Striped Muscle. Fresh muscle. Snip a small piece from the 

 sartorius or gastrocnemius of the frog, tease it in normal saline, place 

 a camel's hair across the fibres, apply the cover-glass and press it 

 down slightly to produce local crushing of the fibres, then remove the 

 hair. 



(L) The fibres are cylindrical and marked with shadowy cross 

 lines, transverse striations, hence called striped muscle. Each 

 fibre is enclosed in a structureless sheath, the sarcolemma y 

 recognisable where the substance of the fibre is crushed and 

 retracted, or where the membrane forms a blister-like pro- 

 jection. Nuclei are difficult to recognise. 



