TISSUES. 89 



of muscle. In tough meat the connective-tissue 

 element is extensively developed and the fasciculi 

 are large and coarse. 



Each muscle fiber has a delicate, transparent, 

 smooth cell wall called the sarcolemma. The oval 

 distinct nuclei lie immediately beneath the sarco- 

 lemma in higher vertebrates, but in lower forms and 

 in all embryos the nuclei lie deeper in the muscle 

 protoplasm. These nuclei have the same structure 

 as the nuclei of any other tissue, but the cytoplasm 

 shows a distinct and regular cross and longitudinal 

 striation, characteristic of only one other tissue 

 the cardiac muscle. The 

 longitudinal striation is /ik 4jij$i&^cohnheim>s 



fa&f, ; ,\ |W ;_>; , S-.-.^-jA area, a bundle 



due to the presence of M Itg] of sarcostyles. 



j i- i-ii 11 J / 31 Sarcoplasm. 



delicate fibrillae called % ^M 



sarcostyles, which is an- ^/^^^ 



alogOUS tO the SpOngio- pfl^W\ Muscle nucleus. 



plasm of other cells. A %il|8l 



., i v-vVf'-^'y^' "* Sarcolemma. 



more homogeneous and ^jSf 



fluid substance intervenes ^w 



between the SarCOStyleS, Fig. 56. Cross section of three 

 n 1 , 7 ... voluntary muscle fibers. 



called sarcoplasm, and is 



in turn analogous to the hyaloplasm of other cells. 

 The sarcostyles are not uniformly or evenly dis- 

 tributed in each muscle fiber, but are grouped into 

 bundles. In cross sections the fiber has therefore 

 a honeycomb structure, the minute areas being 

 known as Cohnheim's fields. A single Cohnheim 

 field represents the cut ends of a single bundle of 

 fibrils or sarcostyles. 



The cross striation is intricate and therefore more 

 difficult to explain. This striation consists of alter- 



