THE MUSCLES. 25 



3. The nuclei. 



4. The sarcolemma is the thin sheath on the outside. 



Look for it where the fibre has been crushed 

 or bent. 



5. The longitudinal divisions of the fibre into many 



small fibrillae are not always visible. 



6. Sketch. 



II. STRIATED MUSCLE. A CROSS-SECTION. 



Material. A slide showing a cross-section of striated muscle that 

 has been hardened in Flemming's fluid and stained in safranin. 

 Apparatus. A compound microscope. 



Examine with the high power of a compound microscope 

 a cross-section of striated muscle. 



Observe : 



a. The arrangement of the fibres in the muscle. 



b. The parts of a single fibre. 



1. The polyhedral areas into which the entire fibre 



is divided are the areas of Cohnheim. 



2. Each area is a group of bundles of fibrillae. The 



granular appearance of each area of Cohnheim 

 is due to the cut ends of the fibrillae. The 

 fibrillse are arranged in columns or bundles 

 which, taken together, make the fibre. 



3. Surrounding each fibrilla and again around the 



columns of fibrillae is a hyaline or slightly 

 granular substance resembling protoplasm, 

 called sarcoplasm. 



III. PLAIN MUSCLE. 



Material. A prepared slide of the fibres of plain muscle. 

 Apparatus. A compound microscope. 



