832 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [86] 



bones that continue the interspinous bones of the dorsal fin as far as 

 the caudal fin. These are five in number and are seen at jf in Fig. 

 25. The rays of the dorsal and anal fin split longitudinally, as I de- 

 scribed them for the pectoral and ventral fins. The anal fin possesses 

 twelve rays in its membrane, and likewise twelve interspinous bones 

 support it, of which the majority in the mid-series have intermediate 

 ossicles as in the dorsal fin. These little bones are each shaped like a 

 dice-bos, and not as Franque has represented them in his drawing. 



My representation of the skeleton of the tail of Amia I have taken 

 so much pains with to secure its accuracy that I believe any verbal 

 description of the parts hardly necessary. (Fig. 25.) More time than 

 usual was devoted to this figure, because the illustrations of this part 

 of Amia's anatomy that it has been my pleasure to examine are far 

 from being correct ; they are carelessly drawn or simply diagrammatic 

 in character (Kolliker's). 



There are twenty-five rays in the caudal fin of this Ganoid. Of these, 

 the two superior ones are very delicately fashioned, the next two are 

 long and slender, while the stoutest ones are found in the middle, from 

 which series they gradually become smaller again as we proceed down- 

 wards. In the j)repared specimen all of these rays are found to be 

 split longitudinally in the vertical plane, and those chosen from near 

 the middle of the member are found to be branched to the third or 

 fourth division. They are also marked at irregular intervals by raised 

 and transverse divisions. The splitting spoken of allows these rays to 

 seize by their anterior ends the hypural bones coming from the verte- 

 bral column, which they do in the manner shown in the figure. In this, 

 the best living example of a masked heterocercal tail, the notochord, 

 being insheathed only in cartilage, has, of course, disappeared in the 

 figure. It is in Polypterus that we find nearly the type of what has 

 been termed the " diphy cereal" tail, in which the notochord is scarcely 

 bent up at all. Our example of Micropterus shows in a marked degree 

 the remaining style of the skeletal parts of the tail in osseous fishes. 

 This is well known to us under the term of the homocereal type, and in 

 this fish shows a very completely ossified urostyle, directed upwards 

 and backwards at an angle of about 45°, with a markedly straight ver- 

 tebral column. The hypural plates are also very broad and i^erfect in 

 this bass, and the fin rays, very similar in construction with those de- 

 scribed for A7nia, are attached to them in the same manner. As in so 

 many osseous fishes, Micropterus has on either side, close to and be- 

 tween the column on the third hypural plate, a sharp, upturned pro- 

 cess. This I believe is intended to afford additional surface and lever- 

 age for the origin of the muscle that controls the movements of the 

 tail. 



In speaking of this part of Amia's anatomy Wilder says ^^ that " the 



^ Wilder, Burt G., Oa the tail of Amia. Proc. Amer. Association for the Adv. of 

 Science, 1876, pages 264-266. 



