﻿54 16 



bone runs out into a fine point which reaches to above the articulation between 

 the 2nd and 3rd vertebrae. 



The second interspinous bone is somewliat in the form of a 7' (PI. II, fig. 1, 2); 

 a thin stem lies in front of the spinous process of the 2nd vertebra, a shorter, 

 anterior T-arm towards the preceding interspinous bone, which however it does 

 not quite reach, and a longer posterior arm which reaches to above the proximal 

 end of the next interspinous bone. In A. strigaia, where the spinous processes are 

 pressed against the neural arches, the stem and the anterior T-arm are almost in 

 contact with one another. 



The interspinous bones 3 and 4 are much stronger, especially 4; they are on 

 the whole the strongest of all the interspinals and appear remarkably heavy in 

 proportion to the thin spinous processes on which they rest; only the proximal 

 part of each is seen distinctly and is for the most part rod-shaped, the remaining 

 part of both is included in and concealed in the large dorsal spine. In all the 

 interspinous bones mentioned as well as in those to be described below, there is 

 a cartilaginous axis through the stem; it is specially thick in these two, 3 and 4. 

 If a cartilage stain is used (methyl-green) we can follow the cartilaginous axis of 

 these two in A. sciitata almost to the end of the large dorsal spine (cf. PI. II, fig. 1). 

 It is thus certain that in A. scutata the spine represents two interspinous bones, 8 

 and 4. The same is the case in the other two species, but here the double nature 

 is also visible externally in the already described longitudinal suture or groove 

 which divides the spine into an upper and a lower part (cf. PI. I, fig. 2). 



Fig. 4. 



Amphisile siriffala Part of the intrrsiiinoiis bont-s 3 and 1. bl. bl' the hlade-Hke portions of 



the l)ones: bf anterior, bl posterioi-, a situation ol' the Musculus eredor. b of the M. di'pressor 



for tlie spinous ray. 



Closer investigation of the interspinous bones 3 and 4 shows, that their struc- 

 ture differs greatly from the usual type more in appearance than in reality. The 

 latter is generally described as dagger-shaped, the laterally compressed blade having 

 on each side a raised longitudinal keel or ridge, separating the anterior muscles 

 (M. anterior s. erector) from the posterior muscles (M. posterior s. depressor) of the 

 ray and at the same time enlarging the surface of attachment of the muscles; 

 through the centre of the spine runs generally a rod-like cartilaginous axis. A 

 glance at Text-fig. 4 ot A. strigata will show (the same can be seen though less 

 distinctly in fig. 1, PI. II of A. scutata), that Ihe blade part /)/ is present lying fairly 

 close behind the point of the spinous process to which these interspinous bones 

 are attached; on 3 however, only the posterior part of the blade bl is present; the 



