ON THE ANATOMY OP FISHES. 
159 
The post-temporal has the usual shape. The ascending process (fig. Gl, 'pt.a.) 
suturally articulates with the dermal epiotic plate [ep.o.) and the pterotic (pt.o.) above, 
while the inferior limb (fig. 59, pt.i.), which is unusually stout, is firmly applied to a 
strong lateral outgrowth from the basioccipital {bo.). The inner surface of the stem, 
and the contiguous portion of the inferior limb, form between them a deep groove-like 
socket for the bifid head of the clavicle, but, as might be expected, no portion of the 
post-temporal has any articular relations with the flexible transverse process of the 
fourth vertebra. The posterior process of the clavicle {cl.p.) is strongly developed, 
and by its extension backwards marks the inferior boundary of the lateral cutaneous 
area of the same side. 
The air-bladder is rather large in proportion to the size of the Fish, and broadly 
ovate in shape, with its anterior third somewhat contracted or pinched in by the 
application of the oval plates of the “ elastic spring” apparatus to its lateral surfaces 
(fig. 60, a.h.). Tiie walls of the bladder are very thin. Internally, the cavity of the 
organ is subdivided in the usual way into an anterior and two lateral compartments 
by primary transverse and longitudinal septa. The transverse septum (t.s.) is a fairly 
stout vertical pillar of fibres, continuous posteriorly with the longitudinal septum (/.«.). 
Dorsally, the transverse septum splits into two bundles of fibres, which pass on either 
side of the body of the sixth vertebra, and at the same time curve forwards as well as 
upwards to the ultimate insertions into tlie lateral surfaces of both the sixth and fifth 
centra. Through the narrowness of the septum, the apertures wdrereby the lateral 
and anterior compartments intercommunicate are unusually -wide. The outer and 
posterior walls of- the lateral chambers are strengthened internally by numerous 
vertically-disposed ridge-like aggregations of fibres, which are stoutest behind, but 
gradually become less marked as they are traced into the anterior chamber, where 
they finally disappear. There is no trace of secondary transverse septa. A ductus 
pneumaticus is present. 
The attachments of the air-bladder, both to rigid and to movable portions of the 
skeleton, are substantially the same as in Macrones. The mesial section of the 
anterior wall of the bladder is attached dorsally to the ventral surface and oblique 
lateral ridges of the complex centrum, to the radial nodules, and also to the feebly 
developed ridges on the ventral surfaces of the crescentic processes of the tripodes. 
Externally to these attachments, and on each side, the fibres of tlie tunica externa 
have the same general arrangement in the lateral and antero-lateral walls as in 
Macrones, and converge in the dorsal w'all in the form of triangular sheets to their 
ultimate connection with the tripodes (fig. 60). The thin median portion of the 
dorsal wall of the anterior chamber is restricted to that part which invests, and is 
firmly attached to, the lateral and ventral surfaces of the complex and fifth vertebral 
centra, inasmuch as, from the peculiar shape of the crescentic processes of the tripodes, 
and the absence of their usually widely open curvature, the oblique posterior margins 
of the triangular sheets are in close relation with those centra. Over a well defined 
