ON THE ANATOMY OF FISHES. 
123 
the gland occupies on each side a recess between the inferior limb of the post-temporal 
and the transverse process of the fourth vertebra, and is in contact dorsally with the 
floor of the saccus paravertebralis and continuous with its fellow by a slender con- 
necting lobe which crosses the ventral surface of the body of the first vertebra. 
A fairly stout ligament stretches transversely between the recurved distal extremi- 
ties of the modified transverse processes, in contact with the proper anterior walls 
of the two air-sacs, but is firmly attached in the median line to the body of the first 
vertebra. 
Neither compressor nor tensor tripodis muscles are present in this species. 
The Weberian ossicles differ but little from those of the more normal species of 
Pimelodinee. The crescentic process of the tripus (fig. 41, trx.), however, has but a 
slight inward curvature. Claustra are present. 
Pimelodiis sapo. 
Both in the structure of its air-bladder and in the modifications of the anterior 
vertebrae and their processes this species presents a singular and somewhat unexpected 
contrast to the more normally constituted species of the genus. 
The complex, the fifth, and the sixth vertebrae are rigidly connected together by 
the growth of superficial ossifications and the partial anchylosis of their neural arches 
and spines. The centrum of the first vertebra (fig. 37, v^) is a comparatively thin, 
biconcave disc, firmly united to the anterior end of the complex centrum. The 
complex and fifth centra are about equal in size, and each is but a little longer than 
the centrum of the sixth vertebra (c.c., v^, and v®). Superficial bony deposit has con- 
siderably thickened the lateral surfaces of the complex and fifth centra, and, to a 
slight extent, the centrum of the sixth vertebra also, so that these centra appear 
much wider as well as shorter than the corresponding elements in the more normal 
species of Fimeloclus. By the ventral and lateral extension of this superficial ossifi- 
cation, the grooves for the dorsal aorta and posterior cardinal veins become converted 
into bony canals {a.c., cd.c.). Immediately behind the anterior opening of the aortic 
canal, the ventral and lateral surfaces of the complex centrum are encircled by an 
obliquely disposed crescentic thickening, in the form of a ridge, which constitutes the 
anterior boundary of a deep but narrow groove, opening laterally on each side into the 
recess enclosed by the modified transverse processes of the fourth vertebra, and 
receiving the anterior margins of the mesial and inner lateral portions of the air- 
bladder. Small radial nodules are suturally attached to the lateral surfaces of the 
complex centrum, and each nodule is in fibrous continuity with a slender spicular 
dorsal lamina having the usual relations to the anterior opening of the cardinal canal 
and to the transverse process of the fourth vertebra. 
Not only is the transverse process of the fourth vertebra {t.p^) greatly expanded, 
but for the proximal third of its extent the anterior margin is bent downwards, and 
R 2 
