noticed by Doyère in iiisecls, and with the "soles" of the nuiscle- 

 tibres of the vertebrates. Only here they are found in a large num- 

 ber on the same muscle-fibre, and only one or two of them serve 

 as a "bed" or "sole" for tiie efferent nerve-endings (fig. 1, fig. 5, fig. 8). 



Through this abundance of sarcoplasm, the curious arrangement 

 of the sarcostyles and the local protuberances of sarcoplasm on the 

 side of it, the muscle-fibre ah-eady acquires a very curious appearance. 

 This is still accentuated by the third fact to be mentioned here, 

 viz. that the muscle-fibres are not the independent, threadlike, straight 

 elements, running from one end of the muscle to the other, as is 

 the case in most of the sceletal muscles, but that in the iris of the 

 birds the muscle-fibres are branched, interwoven, and not only that 

 they divide, but the fibres anastomose through these side-branches 

 (cf. Geberg), so that there is established a continuity of the fibres 

 throughout the whole ring of the iris instead of a tissue containing 

 only distinct separate fibres. This syncytium of sarcoplasmatic elements 

 with bundles of fibrillae running through it in complete continuity 

 over a great distance gives the muscles of the avian iris a striking, 

 resemblance to the cardiac muscle-fibres of the mammalian or avian 

 heart, with the only restriction that in the sphincter iridis the con- 

 nections between the different musclefibres do not come so much to tlie 

 foreground as in the heart muscle, and that the individuality of the 

 musclefibres is better preserved than it is the case in the myo-cardium. 



In connection with this branching, dividing and anastomosing o.t 

 the different muscle fibres of the iris muscle a curious phenomenon 

 may be mentioned here, of which an e,\ample is drawn in fig. 6. 

 When we study tangential (frontal) sections of the iris, in which the 

 whole system of the tibrcs of the sphincter pupillae is shown parallel 

 to the surface, we meet in these sections both the circular fibres 

 running around the pupil (the sphincter pupillae) and the radiating 

 fibres, cut in longitudinal direction. We can state in these sections 

 throughout the whole depth of the sphincter muscle, but especially 

 in the dorsal part of the stroma iridis, the presence of a number 

 of radiating fibres running between the i)undles of the circular fibres, 

 at right angles to the direction of the circular fibres, but lying in 

 the same plain. These radiating mu.scle fibres are apparently independent 

 of the circular fibres, and this is what we should expect, in corre- 

 spondence with the antagonistic function, which we should be inclined 

 to ascribe to the two sorts of fibres. But then this independency is 

 often only apparent, and one often finds a connection between the 

 two sets of fibres, even in the way figured in fig. 0, where a 

 muscle-fibre belonging to the circular system of the sphincter pupillae 



