100 PROF. HOWES OS SYNOSTOSIS Ef FISHES. [Feb. 6, 



faces of those which bound these. That the muscular rather than 

 the skeletal system has been, as it were, at fault, is largely proved 

 by the fact that there is no marked falling off in either the bulk 

 or density of the latter where disturbance occurs ; and the most 

 logical conception of the determining cause seems to me that of 

 an inequality of development, either in bulk or elasticity (and pro- 

 bably the latter), of certain muscles — those affected having either, 

 as it were, lagged behind the skeleton or become fixed in a state of 

 tonic contraction. If this be so, while approximation of the parts 

 of the vertebral column stands out as the ultimate result of the 

 disturbance, we may conveniently at least distinguish between the 

 sinuous condition or approximation by plecospondyly ' (figs. 1 

 and 3), and the compressed one or approximation by symjneso- 

 spondyty a (figs. 5 and 6). 



The specimen last described is of interest in another connexion. 

 Cunningham, in his monograph on the Sole (he. cit. p. 39), gives 

 50 as the total number of vertebra? present, and points out that 

 the first one " is rudimentary'* and possessed of " two small dorsal 

 processes which he along the front edge of the base of the dorsal 

 processes of the second vertebra, but do not unite to form a spine." 

 There can be little doubt that these " dorsal processes " of the 

 first vertebra are but a partially developed pair of neural arches — 

 in the specimen under consideration they are reduced to absolute 

 insignificance (fig. Ah). This greater simplification of the first 

 vertebra is the more interesting, as but 48 instead of 50 vertebrae 

 are present, and as the well-defined characters which diagnose the 

 5th and 11th vertebra? of the normal spine are here realized bvthe 

 4th 3 and 10th. 



P.S., March 1, ls94. — During the passage of these notes 

 through the press, the College of Surgeons' Perch, Xo. 301 (ef. 

 footnote, p. 90) has been dissected, thanks to the kindness of Prof. 

 Stewart. The curvature of its backbone is, most interestingly, 

 identical with that of figs. 2a and 3 6, but of greater amplitude, as 

 is expressed externally by a marked elevation of the trunk cephalud 

 of the first dorsal fin. The vertebra? which mark its vertices 

 number 7-8, 18, and 30. But 39 free vertebra? are present, and 

 the displacement to the left side involves those numbering 20 to 35. 

 Except for a feeble depression of the mid-dorsal region, the contour 

 of the body is regular, and the arches, intermuscular bones, and 

 associated parts are correspondingly modified. 



1 7rXeice(v, to twist ; (nr6v(iv\os, a vertebra. 



2 avfiTTie^eiv, to squeeze together. 



3 In this case on the left side only. 



