53 



The axonost lettered 1 + 2 in figure 17 is also asym- 

 metrical, its head inclining to the eyeless side. As this 

 bone supports two fin rajs (unlike any other in the body, 

 except the hnge axonost 1 of the anal fin), it was carefully 

 examined in a ver^T^ large plaice, and was there seen to 

 present indications of three pieces, two of which possibly 

 correspond to what would represent the first and second 

 axonosts locked together, whilst the third is the partly 

 cartilaginous proximal shaft wedged in between them and 

 connecting them with the skull. If this interpretation of 

 the first apparent axonost be correct, the first baseost 

 (Bs. 1) will be situated between two axonosts as it should 

 be, and not present an anomaly only found elsewhere in 

 the skeleton of the plaice at the anterior extremity of the 

 anal fin. Posteriorly near the head of axonost 1 + 2 is a 

 recess into which fits baseost 1 for the second fin ray. 

 Below this recess is a prominent projection which gives 

 articulation to baseost 2 for the third fin ray. The second 

 fin ray is asymmetrical, the ocular half being the longer. 



The third axonost and fin ray are practically sym- 

 metrical. The head of this axonost forms a cone, the 

 second baseost articulating in front and the third behind. 

 Below the head the axonost bears leafy projections in 

 front and behind. 



In the fourth axonost the leafy projections above are 

 exaggerated and the shaft is reduced to a median ridge on 

 each side of the axonost. This form of the axonost, i.e., 

 with a median spine on each side and thin laminae in front 

 and behind, represents the typical stiucture of an axonost, 

 and is admirably adapted for the muscles of the fin ray 

 inserted into it. As described by Cunningham (pp. 47-48) 

 in the Sole, each fin ray has six muscles, of which there 

 is one on each side (the " right and left abductors '') for 

 deflecting the fin ray to the right aud left of the median 



