1889.] 



Contributions to the Anatomy of Fishes. 



323 



violent excursions of the tripodes which might otherwise take place 

 when the anterior chamber is forcibly compressed by the contraction 

 of its compressor muscles, we would suggest for each the name of 

 " tensor tripodis." 



An " elastic-spriug-apparatus," provided with powerful protractor 

 muscles, has already been described by Johannes Miiller as existing in 

 the South American genera Auchenipterus, Doras, and Puanemus, and 

 in the African Siluroids Synoclontis and Malapterurus. To^ this list 

 our investigations enable us to add the South American form 

 Oxydoras brevis, and the East Indian species Pangasius buchanani, P. 

 cljambal, P. juaro, and P. macronema. The absence of this mechanism 

 in one species of Pangasius, viz., P. micronema, while present in all 

 the remaining species of the genus that came under our notice, is an 

 interesting and noteworthy fact. 



In almost all normal Siluroids the lateral or outer walls of the 

 anterior chamber of the air-bladder are more or less extensively and 

 intimately applied to lateral cutaneous areas, and this relation of the 

 two structures is always brought about by the divergence of the 

 dorso-lateral and ventro- lateral muscles of the trunk, combined with 

 the lateral extension of the anterior portion of the bladder. 



(II.) Siluridce Abnormales. 



Omitting for the present all reference to such extremely aberrant 

 forms as Hypothalmus, Rhinelepis, and the various Loricaroid Siluridee, 

 we confine our summary of this group to the various genera and 

 species that have come directly under our notice. These are : — 

 Clarias, Saccobranchus, Eutropiiclitliys, Cryptopterus (two species), 

 Ailia, Scliilbichtliys, ISilondia, Acrocliordonichthys, Akysis, Pimelodus 

 (two species), Bagarius, Glyptosternum, Amblyceps, Cetopsis, Calio- 

 mystax. 



In all these forms the series of rigidly interconnected vertebras 

 includes only the first, the complex, and the fifth vertebrae, the sixth 

 being almost invariably free. The rigid articulation of the anterior 

 vertebras to the skull is as marked in this group as in the preceding 

 one, and is brought about by precisely similar means. The centrum 

 of the first vertebra is usually somewhat more rudimentary than in 

 the normal forms, and neither it nor the basioccipital or the complex 

 centrum are ever provided with accessory articular processes. The 

 complex vertebra has the same general characters as in the foregoing- 

 group. Radial ridges and nodules are generally but are not invari- 

 ably present ; exceptionally the radial ridge may have no connexion 

 at its inner extremity with the complex centrum (Clarias, Glypto- 

 sternum), and when this is the case the radial nodule maybe absent, 

 or confluent with the inner extremity of the radial ridge and widely 

 separated from the complex centrum (Clarias). 



