18 PEOF. T. JEFFEEY PAEKEE ON THE 



The fifth arch or inferior pharyngeal bone (br°) is unsegmental, but is tipped at its 

 upper end with cartilage. 



The copuloe or medio-ventral elements of the branchial skeleton (cp. 1-cp. 8) are eight 

 in number, three of them (cp. 2, cp. 4, cp. 6) being ossified. 



The first copula (cp. 1) is unossified, bluntly pointed, and supports the tongue. It 

 has been variously called the entoglossal (Stannius), glossohyal, and basihyal (W. K. 

 Parker). The hypohyals articulate partly with it, partly with the succeeding segment. 



The second copula (cp. 2) is a bony plate with cartilaginous ends, broader behind than 

 in front : it is evidently homologous with the segment called by W. K. Parker, the 

 first basi-branchial 1 . Following this, comes a short caritlaginous piece (cp. 3), distinctly 

 segmented from both the preceding and the next following copula?, and excavated on 

 each side by a large concave articular facet for the first hypobranchial. Next follows 

 a well-ossified plate (cp. 4), the second basibranchial of W. K. Parker ; then another 

 cartilaginous segment (cp. 5) with which the second hypobranchials articulate ; then a 

 slender rod of cartilage ossified by a thin flat plate (cp. 6), the third basibranchial of 

 W. K. Parker. So far, the copulse are all regularly articulated with one another. 

 The remaining two, on the other hand, are isolated, or, more strictly, connected with 

 surrounding parts by membrane only : one, a somewhat pear-shaped nodule of cartilage 

 (cp. 7), comes immediately in front of the ventral end of the fourth arch (fourth basi- 

 branchial) ; while the other (cp. 8) is smaller, and is similarly related to the fifth 

 (fifth basibranchial). 



I am disposed to think that the nomenclature of these copula? now generally used 

 is not very satisfactory as applied to Begalecus. According to it, the bone marked 

 cp. 2 is counted as part of the first branchial arch, its midventral or basibranchial 

 segment. Similarly, cp. 4 is considered as part of the second arch, cp. 6 of the third, 

 cp. 7 of the fourth, and cp. 8 of the fifth. But in the present case it will be observed, 

 the only copulas which actually unite the ventral ends of branchial arches are the 

 cartilaginous pieces cp. 3 and cp. 5. On the other hand, each of the segments cp. 2, 

 cp. 4, and cp. 6-8, is interposed between two successive arches, but is itself definitely 

 referable to neither. So that, as the arches themselves are inter-segmental — the 

 segments being determined by the branchial nerves and clefts — the copula? enumerated 

 in the preceding sentence are segmental, bearing something the same sort of relation 

 to the arches that the chevron bones of a reptile bear to its caudal vertebra?. On the 

 other hand, the copula? cp. 3 and cp. 5 are intersegmental like the arches themselves, 

 cp. 3 being definitely referable to the first arch, cp. 5 to the second. 



If this view be correct, the cartilage cp. 3 is the true first basibranchial, and 

 cp. 5 the second. The five copula? ordinarily known as the basibranchials may then be 

 termed interbrancliials. The first copula (cp. 1), judging from the analogy of its 

 successors, in which there is an alternation of inter- and basibranchial (segmental and 



1 " Salmon's Skull," Phil. Trans. 1873, p. 95 ; ' Morphology of the Skull,' p. 80. 



