262 Appendices to Fifth Annual Report 



level of the bridge, it does not do so so rapidly at the tips, and con- 

 sequently these sharp tips look somewhat outwards as well as downwards 

 here. At the 33rd vertebra the hsemapophyses of each side are applied 

 against each other, and fused together in the position of the bridge, which 

 of course, as such, has disappeared, their tips, however, being still apart ; 

 but behind this the haemapophyses meet at their tips, and the long sharp- 

 pointed haemal spine is developed as a single median process. This spine, 

 as is the case also with the neural spine, being due to a separate median and 

 originally posterior ossification which becomes fused with the haemal arch. 



On the haemapophyses, which form the first haemal arch (24th or 25th), 

 is seen the commencement of the formation of the more posterior and 

 strongly prominent articular processes or anterior ventral zygapophyses. 

 This appears first simply as a sharp angle formed on the anterior edge of 

 the haemapophysis, caused by its bending inwards and backwards a short 

 distance below its origin (PI. XVI. fig. 13). On the 28th to 30th vertebra 

 this angle' shows as a distinct but very minute process, and it gradually 

 increases in length, at the 40th vertebra being nearly 2 mm. long, over- 

 hung by, and nearly touching, the posterior zygapophysis of the preceding 

 vertebra. At this vertebra, too, it springs so near the base of the 

 haemapoph3*sis that it seems to arise from the vertebra, to which, in fact, 

 its base becomes partly fused. 



About the 38th vertebra the haemal spines become towards their tip 

 bent more backwards, and the whole arch runs also more backwardly than 

 do those in front. At the 50th vertebra the haemal arch bends so much 

 backwards that it becomes attached near its base by its posterior (and 

 now partly upper) surface to the anterior edge of the vertebra from which 

 it springs. This in the adult looks, except in occasional favourable speci- 

 mens, like a mere fusion of the spine with the vertebra, owing to their 

 close apposition, but examination of very small fish show that a blunt 

 process arises from the posterior edge of the vertebrae, projecting slightly 

 downwards and forwards, and it is these processes — a pair to each vertebra 

 — which, meeting a corresponding slight projection on the upper side of 

 each limb of the haemal arch, fuses with them (Plate XVI. fig. 13, pr.). 

 At this point the posterior (ventral) zygapophyses have almost disappeared. 

 A change occurs in the form of the haemal spine on the third from the last 

 vertebra, which will be described in reference to the caudal fin. 



The Ribs. 



Tw t o sets of ribs may be recognised. The anterior 'fixed' ribs, though 

 ' floating,' in so far as they are quite free at their distal extremities, are 

 to be distinguished by their articulation with the vertebral part of the skele- 

 ton from the posterior 1 free ' ribs, which lie loose, attached only by the 

 intermuscular connective tissue, and unconnected by direct ossification or 

 articulation with any part of the skeleton. 



Along the anterior portion of the basal pieces of the 3rd to the 24th 

 vertebrae inclusive are attached the anterior series of ribs. The first pair 

 of ribs lie close behind, and partly covered by, the pectoral girdle, and 

 they all pass down the sides of the body cavity, terminating with their 

 tips near each other on its ventral edge, but not touching nor in con- 

 nection with one another, otherwise than by intervening tissue. 



The first half-dozen pairs have a short expanded flat scale-like bony 

 projection from their posterior inner edges immediately beyond their heads, 

 which, as in all the others, are formed merely by the blunt end of the rib, 

 a few only being enlarged so much as to warrant the name of a ' head ' 

 (PL XVI. fig. 9, lam., hd). 



