150 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
the complex centrum is exactly paralleled by a precisely similar arrangement in some 
other abnormal Sikiroids {e.g., Clarias). 
The ascending process of the post-temporal (figs. 56 and 57, pt.a.) forms an 
expanded plate at each of the postero-lateral angles of the skull, articulating with 
the pterotic in front, and above with the epiotic and supraoccipital ; the stem of the 
post-temporal slightly overlaps the anterior lip of the distal aperture of the bony 
semicylinder, and is further continued as a tubular prolongation containing the 
lateral line canal along the upper or dorsal lip. From the stem the inferior limb o 
the bone (figs. 55 and 57, 'pt.i.) extends inwards, at first, in contact with the anterior 
wall of the semicylinder, but, subsequently, separating therefrom, passes obliquely 
forwards to articulate with a lateral projection on the surface of the basioccipital. 
At the junction of the inferior limb with the stem, there is a deep groove which 
is almost completely closed behind by the distal extremity of the tubular transverse 
process, and converted into a socket for the clavicle (fig. 55). In a somewhat oblique 
lateral view of the hinder part of the skull and the modified anterior vertebrae 
(fig. 56), the relations of these structures to one another are clearly shown, including 
the formation of the posterior face of the skull by the supraoccipital, exoccipital, and 
epiotic bones ; the convex dorsal surface of the tubular transverse process, and its 
close contiguity to the skull ; as well as the extension of the stem of the post- 
temporal backwards to strengthen the anterior and dorsal margins of the distal 
aperture of the recess for the air-bladder. The slender head of the clavicle may also 
be seen projecting upwards through its tubular socket, near the distal extremity of 
the modified transverse process and between the latter and the inferior limb 
and stem of the post -temporal. On reference to fig. 57, a strong ligament may 
be seen passing from the distal extremity of the posterior process of the clavicle 
ijgt., cl.p.) along the ventral margin of the lateral cutaneous area of its side to an 
insertion behind into the ventral surface of the transverse process of the fifth 
vertebra {t.p}). 
In the outer wall of each auditory capsule, there is a deep basin-shaped depression 
of circular outline, the sides of which are formed by the prootic (fig. 55, pr.o.) and 
pterotic {pt.o.) in front, the pterotic and post-temporal (pt.a.) externally, the epiotic 
(ep.o.) and exoccipital (eo^.) behind, and the prootic and opisthotic plate of the 
exoccipital (e.o.^) internally, while the supraoccipital (so.) occupies the centre of the 
depression. Although a somewhat conspicuous feature in a lateral or ventral view of 
the external surface of the periotic capsule, this curious depression merely serves the 
purpose of affording an extensive surface of attachment for certain muscles connected 
with the branchial arches and pectoral girdle, but its internal effect is to render the 
utricular recess exceptionally shallow when viewed from the interior of the cranial 
cavity. Several of the otic bones, and more particularly the prootics, are so extremely 
thin as to be almost transparent, and the same remark applies also to the opisthotic 
