320 OEIGINAL ARTICLES.' 



The first five vertebras are each furnished with four ribs instead of 

 two ; this is quite a unique arrangement in the osteology of fishes. 

 These supernumerary ribs are attached to the sides of the neural- 

 spine (Owen) far above the neural arch. They are somewhat 

 shorter than the true ribs, which are articulated to the bodies of 

 the vertebrae. But they are so curved, that the inferior end of each 

 reaches to its corresponding true rib, and articulates with the latter 

 near its head. The first supernumerary rib is the longest, and the 

 others gradually decrease until the last, which is the shortest. 



A dense fibrous membrane lines the spaces which intervene be- 

 tween these ribs, so that there exists, on each side of the dorsal spine, 

 and covered over by the superior muscles of the vertebral column, 

 a long conical cavity, whose apex is directed upwards and backwards, 

 and whose base opens downwards into the branchial cavity. In 

 this cavity is lodged a good deal of the branchial labyrinth of the 

 fish. 



The labyrinth of Poly acanthus is not of the complicated nature 

 of that of Anabas, JETelossonia, or Osphromenus, but, in the simplicity 

 of its structure, more resembles that of OphiocepJialus ; it is com- 

 posed of but three heliciform lamellae, which, however, make up in 

 length, what they want in the sub-division of their lamelliform sur- 

 faces, and are so long that they cannot be sufficiently protected by 

 the upper portions of the tympano-maxillary and humero- scapular 

 arches. 



An organ like the labyrinth of this fish, with such important 

 functions to perforin, could not well be lodged in the trunk, where 

 it would be in the way of powerfully acting muscles, but it is quite 

 securely situated, under the rib-like protection of this kind of thorax, 

 formed by the five pairs of accessory ribs. 



No other known Labyrinthoid fish (I have them all in abun- 

 dance) presents a similar anomaly. 



4. Some results of isolated Arterial Injections. 



Isolated arterial injections are in many respects very instructive ; 

 by " isolated injection " I mean the injection of the minute arteries, 

 not of those supplying an extremity, or other large portion of the 

 body ; these latter will never give the same clear idea of the province 

 which belongs to each small arterial branch, whilst the isolated injec- 

 tion of the minute arteries shows the boundaries of the territories, 

 which are irrigated by certain sets of blood-vessels. When an 

 organ receives several arteries, then the isolated injection of each 

 with differently coloured injections, will show, in a most satisfactory 

 manner, what portion of the organ is supplied by each branch. So 

 far as the nervous system is concerned, anatomists have marked out 

 the districts over which the ultimate nervous ramifications spread ; 



