72 
PROFESSORS T. W. BRIDGE AND A. 0. HADDON 
the first four interspinous bones (fig. 2). The succeeding spines are distinct and free 
from root to apex ; they also are cleft to receive the remaining interspinous bones of 
the dorsal fin. 
Between the forwardly inclined neural arch and spinous process of the third 
vertebra, behind and above, the body of the first vertebra below, and the posterior 
margin of the neural plate of the exoccipital in front, there is left on each side 
a somewhat triangular space where the lateral wall of the neural canal is formed only 
by a tough, fibrous membrane, in which the claustrum and the ascending processes 
of the “incus” and “'stapes” are imbedded (figs. 1, 2, 4, and 5). 
Neither the first nor the second vertebra has any trace of transverse processes, 
and in the third vertebra these structures may be represented by the two “ mallei.” 
The transverse processes of the fourth vertebra on the other hand are enormously 
developed, forming on each side of the complex vertebra an expanded wing-like 
lamina of bone, the fiat root of which has its origin not from the centrum, but from 
the whole length of the continuous neural arches of the third and fourth vertebroe 
(figs. 1, 3, and 4, The under surface of each outgrowth is comparatively 
smooth, and slightly concave from before backwards, but its dorsal surface is 
traversed by one or two stout ridges radiating outwards from the neural arch. An 
oval cleft, near the anterior extremity of its distal margin, partially subdivides each 
lamina into an anterior and a posterior division, of which the former is somewhat the 
longer of the two (^.jj.%., The anterior division {t.p^a.) has a thick root, 
continuous behind with the thinner and more lamellar posterior division, which bends 
sliglitly downwards towards its distal end, and is ultimately prolonged into a slender 
free process that curves sharply downwards and then outwards and a little backwards, 
the concavity of the curvature being directed outwards (fig. 3, At the 
extremity of the thickened proximal portion of the division, where the latter joins its 
crescentic distal prolongation, there is an oval facet which looks forwards and 
outwards, and articulates with a similar articular facet on the inferior limb of the 
post-temporal bone, near the ventral margin of the post-temporal plate (figs. 1 and 4, 
Vt.f.). The posterior division {tp.^p.) is broad and comparatively thin, except that 
its dorsal surface is strengthened by a stout oblique ridge extending outwards from 
the neural arch towards the distal margin of the process. Its posterior edge overlaps 
and is partially anchylosed to the proximal half of the succeeding transverse process, 
leaving however the distal portion as a broad, free process of bone (figs. 1 and 3). 
Unlike the anterior division, the posterior is horizontally disposed and bears a 
greater resemblance to a normal transverse process in being directed slightly upwards 
as well as outwards. Except for its greater length, and the width of its root, which, 
like that of its predecessor, springs from the arch of its vertebra, the transverse 
process of the fifth vertebra more nearly resembles an ordinary rib-bearing process. 
The distal end is free, being separated by an oval cleft fj-om the process in front, but 
proximally the two are confiuent (figs. 1 and 3, tp.^). 
