524 Prof. J. C. Ewart. 



widening out cannot be commenced far np, appears to lie between the- 

 utmost improvement of the channel at the expense of accretion on 

 the foreshores outside, and the maintenance of the depths over the 

 foreshores beyond the outlet accompanied with a somewhat less good 

 channel in the estuary. In some cases, deposit on the foreshoi 

 at the side beyond the outlet might be of no importance, and then the 

 river channel should be primarily considered ; but if, on the contrary, 

 accretion on the foreshores outside is undesirable, the outlet must be 

 maintained by a greater widening out of the training walls. The 

 actual direction of the training walls must be determined, in each 

 case, by the general direction of the channel above, the situation of 

 ports on the estuary, the position of the outlet, and the set of the flood 

 tide at the entrance. 



Concluding Remarks. In terminating this record of my investiga- 

 tions, and the general principles for training works which they seem 

 to indicate, I desire to acknowledge the care with which my assistant, 

 Mr. E. Blundell, has carried out the tedious task of working the tides- 

 in the model, and prepared the charts of the experimental results from 

 which the illustrations accompanying this paper have been drawn out. 

 Eddies at sharp edges, due to distortion of scale, appear to have ex- 

 cessive scouring effect in a model; whilst the action of the more 

 regular currents exhibits a deficiency in scouring power, as previously 

 noted. Though the actual depths of the channels, however, are too 

 small for the distorted vertical scale, reliance, I think, may be placed on 

 the general forms and relative depths of the channels obtained in a 

 model. It is possible that the inadequate depth might be remedied by 

 the employment of a finer or lighter material for forming the bed of 

 the model, or by using a liquid of greater density than water ; but 

 sand and water have the unquestionable advantage of being the 

 substances which actually effect the changes in estuaries. 



" Oil the Cranial Nerves of Elasmobranch Fishes. Prelimi- 

 nary Communication." By J. C. EWART, M.D., Regius 

 Professor of Natural History, University of Edinburgh. 

 Communicated by Professor BlJRDON SANDERSON, F.R.S. 

 Received February 22, Read March 7, 1889. 



Although the cranial nerves of Hexanchus, JEchinorhinus, and 

 Scyllium have been fully described, and the segmental value of the 

 nerves of Elasmobranch fishes repeatedly considered, the nervous 

 system of Lcemargus has hitherto escaped notice. This is probably 

 to be accounted for by anatomists taking for granted that Lcemargus 

 agreed in the arrangement of its nerves with Eohinorhinus and other 

 Spinacidce. 



