of the Fishery Board for Scotland. 



117 



arch may be formed also by the transverse processes being united inferiorly 

 by cartilage in the aponeurosis that lines the bottom of the abdominal 

 cavity. More than one case (aeglefinus) was noted where one side only of 

 such an arch was formed : the transverse process on the opposite side 

 did not reach the floor of the abdomen. In minutus the three vertebrae 

 in front of the first haemal arch formed three facultative arches by means 

 of their ribs, which met inferiorly in the tough fascia. In luscus, two of 

 the ribs from the corresponding region formed almost complete arches. 



Asa rule the ribs cease on the anterior side of the first haemal arch, and 

 they are represented behind that point by a film of ligamentous tissue 

 connecting the haemal arches. In virens, however, a rib was found 

 running obliquely downward from the first to the second haemal arch. 



The first arch is the largest, the succeeding arches becoming smaller, 

 rapidly in some species, more gradually in others. The arches all slope 

 more or less backwards. 



The arch bears at its lower end a spine. It is shortest on the first 

 arch, and gradually increases in size in succeeding vertebrae. The haemal 

 spines are long in aeglefinus ; in merlangus, poutassou, and saida they are 

 markedly bent backwards from the arches. 



The first haemal spine is usually attached to the aponeurosis that lines 

 the end of the abdominal cavity, and which binds the ends of the inter- 

 spinous bones. This ligamentous tissue is continued posteriorly, forming 

 the upper edge of the interspinous region. Some of the haemal spines 

 pass through it into the interspinous region, and are attached directly to 

 the interspinous bones. 



The haemal arch always lodges the caudal artery and the caudal vein. 

 It lodges these alone in saida, fig. 60. The kidney accompanies the 

 blood vessels into the arches in all the other species which I have 

 dissected. The conditions in ogac and navaga were not examined. The 

 swim-bladder enters the haemal arches in most of the species, e.g., virens, 

 fig. 74 \ pollachius, fig. 72 ; merlangus, fig. 62 ; luscus, fig. 71 ; minutus, 

 fig. 80 ; poutassou, fig. 70 ; esmarki, fig. 75. In callarias, fig. 91, and 

 aeglefinus, fig. 81, the end of the swim-bladder reaches to the second haemal 

 arch. The swim-bladder does not enter the haemal arches in argenteus, 

 fig. 69, and saida, fig. 60. 



The extent to which the swim-bladder and the kidney enter the 

 haemal arches may be here summarised : — 



Callarias. — The swim-bladder is continued back to the second and 

 third haemal arch. It is bound tightly to the first and second 

 arches ; it is constricted much by the first arch. 



jEglefinus. — The swim-bladder ends at the second heemal arch, to 

 which it is bound firmly below. 



Merlangus. — The swim-bladder is continued backwards to the 8th or 

 9th haemal arch. 



Virens. — The swim-bladder extends back to the 4th, 5th, or 6th 

 haemal arch, tapering to a fine point. It is bound to the 

 first haemal arch. 



Pollachius. — The swim-bladder extends posteriorly to the 10th or 

 11th haemal arch. 



Luscus. — The swim-bladder goes back to the 13th arch; the kidney 



seems to end at the 6th arch. 

 Minutus. — The swim-bladder ends at the 10th arch ; the kidney 



was very small and not noticeable on the outside of the arches. 

 Poutassou. — The swim-bladder extends to the 6th arch. 

 Esmarki. — The swim-bladder ends at the 9th arch. 



