634 J. PLAYFAIR MCMURRirn. 



while in a young Eel (Anguillula acutirostris) it is entirely 

 wanting.^ We can thus fiom these four types construct a 

 scale, passing upward from Anguillula with no ethmo- 

 palatine to Syngnathus with a comparatively small one, then 

 to Sal mo, in which it is more developed, and finally to 

 Clarias, in which it extends back to overlap the pterygoid. 

 The splint bone, which corresponds to and ensheaths this car- 

 tilage, is the maxillary ; and I regret that I have been unable 

 to collect data from which conclusions as to the relative extent 

 of the gape in these forms might be drawn. 



Interesting comparisons can also be made between Stage Din 

 Syngnathus and the cartilaginous skull and arches of 

 Acipenser. In this the relative angulation of the hyoman- 

 dibular is the same, and at the same point as in Syngnathus; 

 the symplectic runs horizontally forward, but is not quite so 

 long, and a very strong resemblance obtains between the 

 pterygo-quadrate in the two forms. In Acipenser, as in 

 Syngnathus, this is represented by a hammer-shaped carti- 

 lage, the basal portion or handle corresponding to the quadrate, 

 the anterior process of the head to the pterygoid, and the pos- 

 terior to the metapterygoid, whifh does not pass back to form 

 a buttress to the hyomandibular. The ethmopalatine seems 

 to be wanting." 



The phylogenetic significance of the teleostean ethmo- 

 palatine is apparently doubtful. Parker and Bridge con- 

 sidered it a structure with no representative in the Selachian 

 jaw, while Balfour^ points out the possibility of its being "an 

 element, primitively belonging to the upper arcade of the 

 mandibular arch, which has become secondarily independent 

 in its development." This suggestion I do not think tenable, 

 and would prefer to side with the later view of Parker and of 

 Marshall, that it represents a prseoral visceral arch, to which 

 the lachrymal cleft and the third nerve correspond. 



1 Ibid. 



^ Tills description has been taken from fig. 241, in Gcgenbaur's ' Elements 

 of Comparalive Anatomy/ London, 1878. 

 • F. M. Balfour, ' Comparative Embryology,' vol. ii, p. 478, Loudon, 1881. 



