170 NOTES ON THE SALMO SALAR SPECIMEN — MORROW. 



59-n. To this vertebral centrum is attached the lower hypural 

 bone, which has a somewhat narrow neck, caused by a foramen 

 on its anterior edge, which passes between it and the ray oti the 

 58th centrum, and a double foramen passing between the pos- 

 terior edge of this hypural bone and the anterior edge of the 

 second ; this double foramen appears to be for the passage of 

 vessels uniting the (pulsating ?) sacks. Also attached to this 

 centrum is the second hypural bone ; it is notched on its ventral 

 anterior surface, by the foramen above mentioned, the division 

 of which is nearly .parallel with the centrum ; this division is 

 caused by a slight projection in the centre of the foramen on 

 this, as well as on the bone already described. At the posterior 

 extremities the adjacent faces of the above two bones are partially 

 rounded, that is, their adjoining corners are rounded off, and in 

 the hollow thus formed, which is slightly above a line drawn 

 through the centre of the spinal column, is a nervous corpuscle,, 

 so shrunken in this skeleton as now to be scarcely observed, but 

 when fresh, it measured three-sixteenths of an inch in diameter. 

 This corpuscle projects slightly beyond the edge of the hypural 

 bones. 



60. Attached to the ventral surface of a spongy centrum is the 

 third hypural bone, and to its end, if indeed it does not belong- 

 to it, is attached the fourth hypural bone, terminating the sixty 

 centra of the spinal column. We have therefore four hypural 

 bones, which being strongly connected together as well as to the 

 posterior ventral rays, form a broad solid plate for the attach- 

 ment of the muscles, and the strengthening of the rays of the 

 caudal fin. The bone lying next above this and completing the 

 spinal column is the urostyle, covering as before mentioned the 

 notochord. 



Prof. Huxley's drawing, representing the tail of the Salmo- 

 published in his " Manual of the Anatomy of Vertebrated Ani- 

 mals," page 20, is incorrect if the Salmo of England is the same as 

 ours'. He makes the vertebral column in this drawing to end in 

 a line common to the anterior vertebras, and at the end of the last 

 centrum which is drawn of greater diameter than those which 

 precede it is attached the terminating bony plate or urostyle,. 



