282 



Appendices to Fifth Annual Report 



ducts, which thence pass forwards on each side of them to enter the 

 exoccipitals.* 



The palato-pterygoid cartilage is not completely ossified. About its mid 

 length is a cartilaginous expanded portion (PI. XV. fig. 1, pl.pt.car.), from 

 which passes forwards a short bar on which is moulded the palatine. At 

 this central point the cartilage articulates with the antorbital ethmopalatine 

 process of the cartilaginous skull. The palatines (fig. 1, pal.) lying on 

 each side of the roof of the mouth extend from this point forwards to 

 articulate by a thickened extremity, where most of the cartilage has 

 ossified, with the anterior processes (trabecular cornua) of the cartilaginous 

 skull and with the maxillae. They are each overlapped posteriorly by a 

 long thin narrow pterygoid (pt.) bent to the form almost of a right angle. 

 Its upper limb is folded round the lower edge of the palatine so as to be 

 partly outside, partly under it, while the downwardly projecting limb 

 has its posterior edge closely applied to, and partly overlapping the 

 anterior edge of the quadrate. At its angle it sends up a short flat 

 spur over the outer side of the body of the cartilage which articulates 

 with the ethmopalatine boss. Lying inside the pterygoid is the 

 meso-pterygoid. An elongated triangular-shaped thin (depressed) bone, 

 it lies with its apex forwards, its inner edge close to the para- 

 sphenoid, its outer edge applied partly to the horizontal arm of the 

 pterygoid, partly to the tip of the quadrate. Its posterior rounded end 

 (forming the base of the triangle) overlaps, and is closely attached to the 

 upper part of the metapterygoid. The broad aspect of the bone, there- 

 fore, faces upwards, and it is bent downwards slightly towards its centre, 

 and forms the anterior two-thirds of the floor of the orbit. 



The quadrate (PI. XV. fig. 1, qu.) has the form nearly of an equilateral 

 triangle, its apex upwards, and the slightly downwardly curved base below. 

 Its anterior straight almost vertical edge is closely applied to and partly over- 

 lapped by the posterior edge of the metapterygoid, while its lower anterior 

 angle is truncated to form an articular cavity for the lower jaw. With 

 the anterior part of its ventral margin is connected the lower part of the 

 preopercular bone, and a groove on the inside of its ventral margin receives 

 the symplectic. 



Connected by its anterior border with the posterior edge of the quadrate 

 is the thin metapterygoid (mt.pt.\ its base being continuous with that of 

 the latter bone. It also has an irregularly triangular shape, its anterior 

 and ventral margins forming nearly a right angle, its apex (dorsal) in con- 

 junction with the apex of the quadrate, while its third side (postero-dorsal) 

 spreads out dorsally in its posterior two-thirds into a flat curved portion, 

 with a projecting process lapping outside a corresponding curved process 

 on the hyomandibular's anterior face. This portion forms part of the 

 posterior floor of the orbit, being continuous here with the mesopterygoid. 



The hyomandibular (PI. XV. fig. 1, h.mn.) consists of a strong thick bone. 

 The square-shaped upper portion articulates along its dorsal end, with the 

 cavity underneath the projecting edge of the sphenotic and pterotic. From 



* These ducts are contained in a pair of cartilaginous rods, which pass into the 

 exoccipitals as already described. They are rather flattened, being of an oval form 

 in transverse section, and measure (according to the size of the adult fish) about '25 

 mm. by *35 mm. in diameter. The central perforation for the membranous duct is 

 •08 mm. in diameter. Nearly the half of this space is occupied by the walls of the 

 duct, and as it is very difficult to keep the latter perfect in its whole length, this 

 probably accounts for Valenciennes' failure to force air through it. This is no 

 sufficient reason for the assertion by Valenciennes, of its non-tubular character, 

 which I have disproved by a series of sections from end to end. The cartilage 

 formed round the duct is sometimes found partially incomplete in the larval herring, 

 its development being rather irregular. The ducts meet posteriorly, having a single 

 aperture to the anterior end of the swim-bladder. 



