QQ DK. AV, G. RIDEWOOD ON THE CRANIAL [May 3, 



the opisthotic limb of the post-temporal. In Osteoglossum also 

 thei-e are two important intermuscular bony brushes on each side. 



These osseous brushes are probably far more common in their 

 occurrence than is generally suspected, and the reason that they 

 have not attracted more notice in the past is probably due partly 

 to the fact that anatomists have been disposed to discount their 

 value as constituents of the skeleton (although they are just as 

 important as epipleural bones, which are not disregarded when 

 dealing with the vertebral column), and partly also because the 

 preparateur dissects them away from the back of the cranium 

 when removing the skull from the vertebral column, and they 

 thus become thrown away with the muscles of the trunk. They 

 have been noted, however, in the Black Bass and the Tunny by 

 Shufeldt, who calls them "occipital ribs" (Rep. U.S. Fish. Com. 

 1883 (1885), p. 805). Hyrtl (Denkschr. Akad. Wiss. Wien, xxi. 

 1863, p. 3), with considei-able acumen, has likened those at the 

 back of the skull of Ghanos to the ossified tendons of birds. 



Such intermuscular brushes are not confined to the exoccipital 

 and opisthotic bones. In Chatoessus they occur on the supra- 

 occipital and epiotic prominences, and in Chanos the supraoccipital 

 spine is produced back into a bony brush exactly similar to that 

 of Chatoessus, except in that it is not a separate structure. In 

 Gonorhynchus the posterior end of the outer intermuscular bone 

 is connected with the post-temporal by means of fibrous tissue. 

 There is no opisthotic limb of the post-temporal besides this, 

 which is clearly the opisthotic limb which has failed to establish 

 the usual osseous connection with the post-temporal. In Albiola, 

 in addition to a f uUy developed opisthotic limb, there is an ossified 

 tendon which projects forward from the inner surface of the post- 

 temporal bone into the posterior temporal fossa, where it branches 

 among the fibres of the trapezius muscle. 



The supratemporal may in a genei-al way be described as that 

 dermal bone which receives the lateral line from the post-temporal 

 and transmits it to the squamosal, and gives off a branch to the 

 parietal (e. g. Glupea), or to one or more tubular scales of the 

 transverse commissure of the sensory-canal system separable from 

 the parietal (e. g. Alhula. Salmo). The form of the supratemporal 

 is thus triradiate. In Gonorhynchus, however, in which also the 

 commissural scales ai'e separable from the paiietals and supra- 

 occipital, the foi'king of the canal-system occurs just in front of 

 the supratemporal, so that this bone is a plain tubular scale. 



The supratemporal is a bone which lies either above or posterior 

 to the squamosal ridge, and either below or external to the epiotic 

 ridge ; and Collinge (Proc. Zool. Soc. 1895, p. 291) is undoubtedly 

 right in questioning the correctness of Parker's application of the 

 term supratemporal to that bone of the lateral-line system which 

 in the Salmon lies above the preopercular and below the squamosal 

 ridge (Phil. Trans, vol. 163. 1873, p. 99, and pi. 6. fig. 1, st). 

 Parker's "supratemporal" appears to correspond exactly with 

 that bone which in Ghanos lies immediately above the opei'cular 



