MORPHOLOGY OF TELEOSTKAN HEAD SKELETON. 577 



branchials and the fourth epibranchial are absent. The 

 pharyngobranchials of the second to fonrth arches are 

 present, but, unlike those of Gasterosteus, the first two are 

 fused; the third is free, and all are rod-like, and lie one 

 behind the other. In Sjmgnathus the first and second 

 basibranchials and the second hypohranchial alone are 

 present; the fonrth epibranchial has gone, but the edentulous 

 pharyngobranchials, though rod-like, occupj^ tlie same position 

 relatively to one another as in Gasterosteus. 



In the liyoid arch the basihyal, though present during 

 development, is absent in the adult Syngnathus, but attains 

 a great length in Fistularia. 



Of the bones immediately concerned in the gill-cover and 

 branchiostegal membrane, the operculum alone survives in 

 Syngnathus, but are all present, together with five branchio- 

 stegal rays, in the Fistularia. The interoperculuni, which 

 McMurrich failed to recognise as such, bears, by reason of its 

 position, a superficial resemblance to the gular plates of 

 Polypterus, and was mistnken for such by Parker (68). 

 Otherwise, as in Fistulariiv, it is quite normal in its relation- 

 ships. 



In describing the other suspensorial bones, McMurrich 

 mistook the pre-operculum for the infra-orbital, and con- 

 sequently went wrong in his identification of the rest. The 

 true infra-orbital, or rather the first bone of the suborbital 

 series (fig. 50, so?), articulates with the parethmoid ((3. p. b.) 

 above, and foi-ms the lower border of the narial opening. 

 Ventrally.it appears to divide into two lamina3, lying on the 

 outer and inner sides respectively of the cheek muscles, and 

 is attached by its lower border to the combined symplectic 

 and pre-operculum {sym. + o.pr.). In front of the latter lies 

 the greatly extended quadrate (qu.), of which only the small 

 part indicated by the dotted line originated by ossification of 

 cartilage. Along its upper and anterior borders lie three 

 bones, a, b, c, whose homologies are uncertain ; b and c 

 together have all the relationships of the pterygoid in the 

 stickleback, but as h is developed in relation to the vestigial 



