246 



Mr. J. A. Ryder on the 



twice at each of the points c and c and along the line a, h^ 

 where the middle limb of the ^ rests. 



The only point which now remains to be discussed is the 

 imbrication of the scales. This is also as readily accounted 

 for as the delimitation of the scale-forming areola3, s, s, s, and 

 their trilinear arrangement in three directions in the convex 

 surface of the integument by means of the mechanical hypo- 

 thesis here outlined. If we were to make a longitudinal 

 transverse section through a fish along the ])lane of the letters 

 c, c, c, or c', c', c' of fig. 1, we should get a section like fig. 2, 



Fig. 2. 



Ym. 3. 



B 3- 3 3 4 S 6 7 P. ■'} 



in which the myotomes M, M, M, &c. (fig. 2) were again 

 found to be V-shaped on either side of the medial axis or 

 vertebral column, c, c (fig. 2) . This proves that the myotomes 

 are really cones fitting into one another, and that, if we 

 suppose the first one to be inserted into the base of the skull 

 along the line A^ B (fig. 2), that point becomes the anterior 

 fulcrum or point d^appui oi the whole muscular system. The 

 tensions thus developed upon tlie skin along the successive 

 myocommata 1, 2, 3, &c. (fig. 2) are such that the integument 

 would be flexed inward opposite each myocomma as shown in 

 the next figure on a larger scale, which represents the foldings 

 of the integument at the surface of a part of fig. 2. Here in 

 fig. 3 the myocommata m, i' , m^ i\ ???, &c. are seen to be 

 inserted upon tlie 

 internal face of the 

 epidermis. The 

 membrane »2, ?«, w, 

 »?, acted upon by 

 the muscular fibres 

 of the myotomes M, 

 JVIjM, wHl have the 

 effect of pulling the / 



integument inward / 

 in the direction of /-i' 



the arrows «', ^', 



from the linear ' V ^ v \ i^ '' 



points of attach- 

 ment of the myocommata to the integuments at ^', «', t', toward 

 the vertebral bodies V, V, V. In this manner will be deve- 

 loped the imbrication indicated by the heavy border along the 

 posterior margins of the scales s, 5, s in fig. 1, and in fig. 3 in 

 longitudinal section through the scale-sacks or pockets at 5, 5, s. 



