﻿19 57 



The tendon of the elevating muscle (M. anterior s. erector) passes out between 

 the ends of the interspinous bones 3 and 4 and is attached to the base of the ray 

 above the cleft; the tendon for the flexor, M. posterior s. depressor, passes out 

 through a separate opening on the under side of the interspinal 4 (see fig. 8), but 

 is covered below by the broadened base of the plate /; the tendon is attached to 

 a small process at the base of the ray. Fig. 8 shows this part of the interspinous 

 bone 4 seen from below. The end of this is hollowed out, spoon-shaped on the 

 under surface; at the bottom of the spoon opens the 

 canals for the depressor muscles; to its margin is apposed 

 the margin of the spinous piece t; the tendon passes out 

 to the ray between this and the interspinous bone. 



In A. scutata the various parts composing the spine 

 have become unrecognisable through fusion; not only, , ^^,^ ^ 



further, is an articulated spinous ray wanting, but also ^^^-^f 

 the special pieces, lateral plate / and the spinous piece t Fig. 9. 



which are present at the joint in the other two. Whether ''"'''' "''!""« Himi e.ui or dorsal 



'^ •" spiili'. sc'fil from the side. 3, i 



the spinous ray and the other parts have simply fallen interspinous bones .5 ami 4; spinous 

 out in scutata, or have fused in rudimentary foi-m into ™^' "'" "f J;,~;f '''''''' "''' 

 the point of the dorsal spine must be left unsettled. The 



extreme end of the dorsal spine seems to me very variable both in outer form and 

 inner structure; in some specimens the cartilaginous axis may be detected almost 

 right to the tip, in others the last 1 — 2 mm. consists solely of bony substance, 

 reminding one of the spinous ray in the other species. To this must be added, 

 that HiLGENDORF (17) in specimens from New Britain has found a small spine 

 under the tip, ca. 1 mm. from this, obviously the same small spinous piece / 

 which is characteristic of the other two species. I may mention that Hilgendorf 

 considers these specimens as a special species, which he calls A. finschii. 



In the second group of interspinous bones (cf. PI. II, fig. 1, 5, 6, 7), the three 

 which are placed in front of the spinous processes 7, 8 and 9 are long and thin 

 and extend as stays through the membrane of the first dorsal fin; in scutata all 

 three, in strigata the two seen externally, have a distal compressed part more or 

 less lancet-shaped (but the form is not very constant). These stays have hitherto 

 been generally regarded as spinous rays, both by the few authors who have seen 

 that they extend right in between the spinous processes, and by the majority who 

 have kept to the outward appearance. With a cartilage stain or simply under the 

 microscope the cartilaginous axis can be seen running out more or less to the lip; 

 as far as the cartilage reaches, at any rate, there can be no talk of anything but 

 interspinous bones, but the condition in Centriscus (see later) seems to indicate 

 that the hard, shining and solid lancet-point beyond the cartilage may be regarded 

 as a short spinous ray fused with the interspinous bone. 



The interspinous bone in front of the spinous process 10 has no ray (fig. 1, 

 PI. II); proximally it has the same appearance as the foregoing, but distally it ends 



