By tliis cross-striatioii the niiiscle-(ibres of the iris and the corpus 

 ciliare ma}' be compared with the group of voluntary mnscle-fibres, 

 but when we study somewiial more closely their form and structure, 

 there appear quite a numl)er of minor differences, which bring them 

 into a closer vicinity to the heart-muscle fibres. 



In the first place tlie muscle-flbres of the iris and the corpus 

 ciliare. as was shown as far back as 18H3 by Gkberg, do not possess 

 the tough, thickened cellmembrane commonly known as sarcolemma. 

 Here the plasma and the myolibrilla contained in the sarcoplasma 

 are surrounded by an exti'emely thin and delicate membrane, rein- 

 forced by the closely applied bodies of connective-tissue cells, and 

 often it is practically impossible to demonstrate the membranous 

 covering of the fibres, which might be called a sarcolemma apart 

 from this connccti\e tissue. 



In the secojid place these niuscle-librcs contain a very considerable 

 amount of sarcoplasm and only a comparatively small number of 

 contractile striated flbrillae. The.se librillae are usually gathered toge- 

 ther into a number of columnlike or platelike bundles, which we 

 may call with Sciiafkr among others the sarcostyles. 



Ill tliiii iiniscle-libres these fibrillMindles are distributed rather regu- 

 larly lliroiighoul the whole muscle-fibre, and, when cut in transverse 

 sections, present liie picture of fig. 1 and fig. 'A. 



In the larger muscle-fibres lhe.se librilbundle.s or sarcostyles are 

 arranged in a curious manner, in flattened bundles, folded or curved 

 romiil, and lying in a large amount of sarco|)lasm ; the structure 

 Fig. 1. Fig. 2. 



Fig. 3. Fig. 4. Fig. 5. 



Fig. 1 — 5 cross sections of muscle-fibres of liie muse, sphincter 

 pupillae of a full-grown fowl. Magn. 1G00. 



1* 



