884 



Fig. 1. Section of the fish, in which the muscle-knob 

 is to be seen. The knob is divided into two parts, which 

 diverge in the proximal direction and make by doing 

 so the impression in the lower section as if there were 

 two single knobs. 



The fibrous tissue between the muscle fibres had increased ; the arrangement of 

 the great septa of connective tissue pretty well agrees with normal proportions, but 

 the thinner bundles surrounding the separate muscle fibres are often irregularly and 

 considerably thickened. 



In some places in the connective tissue an accumulation of small cells with 

 round irregularly coloured nuclei and a small quantity of prol opiasm is to be found; 

 other sections show much fatty tissue with rests of degenerated muscle fibres. 



Neither haemorrhage nor bloodpigment could be stated. 



Studying the structure of the muscle fibres, the question arose how the normal 

 dorsal muscles of Pleuronectus were built. It is well known that fishes normally 

 show peculiar grouping of the bundles of fibrils and this in such a way that the 

 fibres of a given muscle group in a given fish species ordinarily have in this 

 respect a characteristic structure. 



Lansimaki M, who studied this question carefully, found in the dorsal muscles of 

 Pleuronectus that each fibre showed in its exterior part a thin layer of ribbon- 

 shaped bundles of fibrils, whilst the inner part was filled up with cylindric bundles. 



In self-made preparations of a normal plaice 1 could confirm these statements 

 (Fig. 2). 



In the preparations of the muscle-knob the fibrils are generally coarser than 

 normal; the transverse striation, however, shows the usual dimensions, and is in all 

 non-degenerated -fibres distinctly visible. The typical normal form and grouping of 

 the bundles of fibrils is in the various smaller fibres clearly to be seen, the big 

 fibres however do not often show the peripheral ribbon-shaped fibrils. Some very 

 small fibres possess only ribbon-shaped bundles which form a starlike figure in 

 transverse sections. 



In longitudinal sections one can see that the fibres here and there give off greater 

 and smaller branches. The myoplasm has in some places a little increased in volume. 



The muscle-nuclei are in the smaller as well as in the bigger fibres not more 

 numerous than normal generally they are situated at the periphery, but sometimes 

 also between the "fibrils; the nuclei are somewhat swollen; nuclear divisions could 

 not be detected. 



Among the big non-degenerated fibres many show a curious and striking struc- 

 ture. In transverse sections they seem to consist of two concentric parts : the inner 



1) T. A. Lansimaki (Helsinfors) Ueber die Anordnung der Fibrillenbundel in den 

 quergestreiften Muskeln einiger Kische. Anat. Hefte. Heft. Ii26, S. 254. 



