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of (ho horly. Af tlio placo of iii(oi-i'ii|)(i()ii sopla oC coniicclive tissue 

 tleseend Jiiul seem to dixidc (lie myotome iiilo three |>arts. One 

 part situated between llie mid-dorsal line and the line /./. is the 

 dorsal part of th(» myolome: between the Hues /,/, and /.'// lies 

 the lateral and l)e(ween the latter and the mid-\enti'al line, the 

 ventral i)art of tho myotome is silnaled. 



Considered at the line of interruption, the surface of ijie lateral 

 part of the myotome seems to be eranially displaced in respect to 

 the dorsal part: this displacem(Mi( amouids to one half of the bi-eadth 

 of the myotome. The same can be obsei-\ed between the sui-face 

 of the lateral and the Aeidi'al i)ar1 of the myotome, the lateral part 

 being also dis])laced eranially in i-es[)ect to (he \enli-al part: this 

 displacement does not surpass 7» of the breadth of the myotome. 



If we follow the sojita of connective tissue at the line of inler- 

 rn[)tion l^L, it is easily seen, that the myotome is i-olled in (owards 

 the axis of the body and then reversed till it i-(\xches agaiji (he bodv 

 surface. In most cases the continuity of the muscular tissue at the 

 bottom of (he fold is broken oil'. bu( (he in((M-sei>-mcn(al (issue which 

 covers the myotome is always conlinuoiis. If we now try (o unroll 

 the myotome as mnch as possil)le, we lijid (ha( (he dorsal j>art 

 makes an angle with (he latei-al part, so that a (rue knee is formed. 

 The top of the knee is directed towards (he head as in Pctromyzon. 

 The line along which the myotome is folded in, is parallel (o (he 

 sagidal axis of the body, and seems to run ovei- (he knee, so that 

 the toi) of the knee lies at the point K of tigure V'l. 



The same can be observed on following the \\\w L' L' ((ig. \T), 

 the line of folding being also i)ai'allel to (he sagi((al axis of (he 

 trunk. 



The differentiation of the myotome into three parts, ensues there- 

 foi'e from a process of iid"olding, the lines of folding being pai'allel 

 to the sagittal axis of the body. 



If a model of the myotome of Petromyzoii is cut out of paper, 

 and this myotome folded in along (he lines FF and F' F' 

 (tig. II), we get a precise illus(i"a(ion of the disj)lacements seen 

 in the myotome of Acaidhias. The direction in which (he ou(er- 

 surfaces are dis])laced in respect to each other is a direct consc- 

 cpience of the form and the curvature of (he myolcune a( the 

 places of infolding. The diffei-ence in the extent of the displacement 

 of the surfaces along the lines LL and //// (tig. \'l) is due 

 to the fact, that the fold along the line hF is longer in the diicction 

 from outwards (o inwards in corres|K)ndence with the dimensions 

 of the myotome. This can be seen in a transverse section through 



