( 3ft ) 



^'"'g- ^'H- tlie same region of flie trunk 



of Aeanthicxs, wliei-e LF (iig. 

 VII) is the intersegmental tissue 

 that divides tlie dorsal from the 

 lateral part, while L' F' is the 

 septum, that the latter separates 

 from the ventral part of the 

 mvotome. 



The further differentiation of 

 the dorsal part of the myotome 

 takes places by the same process; 

 the lines of folding instead of 

 being parallel to the sagittal 

 axis of the body are in general 

 at right angles to this axis. 



There are three of these lines, 

 agreeing with the number of 

 peaks which the dorsal part of 

 the myotome shows. These lines 

 considered from outwards to 

 -.C.V inwards, are originally normal 

 to the surface of the body, tlien 

 Transverse section tluoiigli the trunk curved with the convex side 

 of Acanlhias: tlie intersegmental tissue turned veutrally and towards 

 black. Natural size. i|„^. body surfaces. This cui-xa- 



ture is most marked in the third line of folding (M fig. VII), reckoned 

 from the mid-dorsal line, the first one being nearly a straight line 

 normal to the body surface and to the sagittal axis. These lines 

 of folding ai'c visible on a transverse section, because septa of inter- 

 segmental tissue stretch out into the fold. The curved lines (.1 (ig. MI) 

 are the transx'erse sections of these septa. 



The lateral part of the myotome shows no further difTerentiations. 

 The ventral part has only one line along which the folding of the 

 myotome is well marked ; consequently this part of the myotome 

 shows only one peak turned to the caudal end of the body. 



The myotome considered as a \vhole, as in Petromyzon, has a 

 caudal inclination. This inclination is most marked at the knee. 

 Considering only the dorsal part, we see this inclination diminish 

 towards the mid-dorsal line, so that the most dorsal part of the 

 myotome is about normal to. the sui-face of the l)ody. This most 

 dorsal part is elongated into a dorsal cornu [CD fig. VI). In trans- 



