266 



Appendices to Fifth Annual Report 



This simple form of the bones and their arrangement becomes more 

 complicated along the latter half of the body. The 24th intermuscular 

 (that of 25th vertebra) becomes bifurcated. 



About 4 mm. (in the 292 mm. herring), from its proximal end, there 

 arises from its outer side a bony branch which runs upwards, though in the 

 same plane, i.e., between the myotomes, terminating in the connective 

 tissue close to, and therefore practically attached to the tips of the lateral 

 appendages of the hsenial arches (the transverse processes). This branch, at 

 first a mere process 1 to 2 mm. long, increases in length posteriorly. The 

 head of the main stem gets shifted further and further downwards, and 

 consequently also backwards, so that at the 30th vertebra we find the 

 tip (or as it now really is the head), of the branch just described lying 

 nearest the original position of the head of the main bone, viz., near the 

 outer side of vertebral column ; the original head being ventral to it, and 

 some distance from the vertebra, and attached near the tips of thermal 

 spines. This rearrangement becomes most pronounced at the 36th rib ; 

 for the branch bone has not only been getting longer and longer in conse- 

 quence of its tip retaining its original position, while the main stem from 

 which it arises has been getting more and more ventral ; but in consequence 

 of this it has come to lie more and more in line with the distal portion of 

 the original stem, and the proximal part of the latter here strikes inwards 

 so sharply as to form a considerable angle with its distal portion (PI. XV. 

 fig. 1, b.i.m.). The appearance of this 36th intermuscular, therefore, would 

 lead to the supposition that what we know to be the original proximal part 

 was a branch of the remaining portion which forms a slightly curved and 

 continuous bone. This real head of the bone, however, is still as at first 

 connected more directly with the skeleton by the connective tissue, than 

 is the case with the original branch which gives attachment along its 

 length simply to the intermyotomie fascia. 



Towards the end of the tail the myotomes both narrow, and come to lie 

 so much more longitudinally than on the body proper, that the inter- 

 muscular bones become more closely approximated, and lie almost parallel 

 to the vertebral column. In the adult herring about 40 or 50 mm. of the 

 terminal caudal portion of the fish is, on each side and beneath the super- 

 ficial red muscles, completely sheathed by these bones, which have now 

 lost their curvature, and gradually shorten to the last, which in the 292 

 mm. long fish is about 12 mm. in length. 



In this position each of the ventral intermusculars (those dorsal to the 

 vertebral column will be referred to below), principally consists of what 

 originally was its outer branch, continuous with the shortened distal part 

 of the original bone ; while the inner branch — the original head of the 

 intermuscular — has been getting shorter and shorter, although still attached 

 to the haemal spines. At the 47th vertebra, in the herring always referred 

 to, the outer branch was 12 mm., the inner 3 mm. long, attached by 

 a ligament 4 mm. in length. At the 48th vertebra the inner original head 

 is a mere process attached by 6 mm. long ligament, and on the 49th 

 process and ligament have disappeared. 



These laterally placed terminal intermusculars are present as far back 

 as corresponds with the 54th, beyond which they are only represented by 

 connective tissue. 



In describing the neural arches, it was said that a change occurred in 

 the form of their lateral processes at the 22nd or 23rd vertebra, viz., that 

 instead of — as is the case on the previous arches — springing from and 

 being completely ossified with the bases of these, they are attached to them 

 only by connective tissue — they in fact become exactly similar to the 

 intermuscular bones of the lower part of the body. These neural appen- 



