ON THE ANATOMY OP FISHES. 
175 
The relatively feeble development of the shoulder-girdle in Malapterurus, and the 
laxity of its connection with the skull, are obviously correlated with the absence of 
the large pectoral spines which are so characteristic of most other Siluridee. The 
post-temporal is but loosely connected with the skull, its ascending process being 
movably connected with the pterotic and epiotic bones by ligament, while the 
articulation of the inferior limb with the basioccipital is of a similar character. The 
clavicular groove is so slight as scarcely to deserve the name of socket, the connection 
of the clavicle and post-temporal being mainly effected by strong ligamentous fibres. 
The air-bladder (fig. 71) consists of two divisions, a relatively small anterior one, 
which represents a normal bladder, and is divided into an anterior {a.c.) and two lateral 
(Z.c.) compartments by a primary transverse {t.s.) and a longitudinal {l.s.) septum ; 
and a somewhat larger posterior sac (p.c.), oval in shape, and extending backwards in 
the abdominal cavity nearly as far as the anus. A contracted tubular portion connects 
the two divisions, and the longitudinal septum {l.s.), which separates the two lateral 
compartments anteriorly, extends also through the tubular isthmus and the posterior 
sac, and subdivides the cavity of the latter into a right and left chamber. The 
posterior sac {p.c.) has the shape of a much elongated oval ; its walls are moderately 
thick, but strengthened internally by a number of transversely arranged circular 
fibrous ridges which project freely into the cavity of each of its chambers. The 
anterior division of the bladder is somewhat cordate in shape, a deep notch in the 
median line of its anterior wall partially dividing it into two laterally and forwardly 
bulging halves. The transverse septum {t.s.) is rather narrow, but widens out to 
some extent before blending with the ventral wall of the bladder. The anterior 
chamber {a.c.) is greatly constricted longitudinally in the median line, first, by the 
deep notch in its anterior wall, and, secondly, by the unusual prominence of the 
medio-dorsal ridge which results from the impression of the subvertebral keel ; hence 
it is that the lateral halves of the chamber intercommunicate by a comparatively 
small aperture. Both the anterior and lateral compartments have relatively thin 
walls, and the latter exhibit no trace of secondary transverse septa. 
In the disposition of the fibres forming the walls of the anterior chamber, and in 
their relations and attachments to fixed or movable portions of the skeleton, 
Malapterurus differs in no essential feature from Macrones. The skeletal insertions 
of the posterior pillars are shown in fig. 71 {p-p.). The dorsal portion of the primary 
transverse septum {t.s.) splits beneath the centrum of the fifth vertebra into two 
diverging bundles of fibres, which pass dorsally, one on each side of the centrum, 
and eventually, after curving forwards into the dorsal wall of the anterior chamber, 
become firmly attached to the lateral surfaces of the complex centrum, to the 
posterior margins of the dorsal laminae, and to the prolongations of the latter on to the 
ventral surfaces of the transverse' processes of the fourth vertebra. Unlike Oxydoras 
and Auchenipterus, the walls of the anterior chamber are not specially thin where 
the oval plates of the “ elastic-spring ” mechanism are applied to them. A transverse 
