34 PKOF. T. H. HUXLKY ON CKRATODUS FORSTERI. [Jan. 4, 



side of the symphysial end of Meckel's cartilage, and unites with a 

 corresponding surface furnished by the expanded symphysial end of 

 the bone, termed "dentary" by Dr. Gunther. I cannot doubt that 

 this bone is the representative of the true " dentary " element ; nor is 

 there any question in my mind that Dr. Gunther' s "dentary" is the 

 true " splenial " element, while his articular answers to the "angu- 

 lar" piece of the vertebrate mandible. In the attachment of the 

 tooth to the splenial, and not to the dentary, element, Geratodus 

 presents an interesting and important feature of resemblance to Siren 

 and to larval Salamanders on the one hand, and, on the other, to 

 Polypterus. 



The splenial element in this Ganoid resembles that of Geratodus, 

 not only in bearing teeth, but in form, position, and relative size. 

 In a young specimen of Polypterus I find that the splenial does not 

 extend continuously to the symphysis, but that, between its anterior 

 termination and the latter, there are two short and broad bony plates 

 developed in the fibrous tissue which overlies Meckel's cartilage ; 

 these bear teeth, and correspond with the expanded symphysial end 

 of the splenial in Geratodus. Polypterus has a true articulare, from 

 which Meckel's cartilage is continued. The angulare is much 

 shorter, and the dentale much longer than in Geratodus. 



The hyoidean and opercular apparatus present characters of sin- 

 gular interest. Dr. Gunther says that " on the hinder side of the 

 tympanic pedicle*, near its base, there is a small round tubercle, for 

 the suspension and articulation of the hyoid arch (pi. xxxiv. 

 fig. 3, »)." 



I presume that this " small round tubercle " of the suspensorial 

 expansion of the cranium is the small cartilage marked H.M\i\ figs. 

 4 and G. But this is neither a process of the suspensorium, nor does 

 it articulate with, nor take the principal share in, suspending Hy, 

 which is Dr. Giinther's "hyoid arch." 



In fact it is, as fig. G shows, a distinct, though small, four-sided, 

 flattened cartilage, the anterior and ventral angle of which is produced 

 into a short conical process (Sy). Its anterior edge is firmly united 

 with the skull, just where the cranium proper passes into the sus- 

 pensorium. At this point there is a triangular vacuity filled with 

 fibrous tissue, through which the posterior division of the seventh 

 nerve passes (figs. 1 and 6, VII). The outer face of the cartilage is 

 loosely connected with the operculum (Op) ; and the conical process 

 (-Sy) is imbedded in the dorsal and posterior part of the powerful 

 ligament (h.s) (corresponding with the hyosuspensorial ligament in 

 Menobranchu&f) by which Hy is mainly kept in place. 



It is obvious that this little cartilage is the homologue of the hyo- 

 mandibular element of the hyoidean arch of other fishes, the small 

 conical process being the rudimentary symplectic, and, therefore, that 



* It is surely to be regretted that any writer of authority should retain the 

 misleading name of "tympanic pedicle" for a part the total distinctness of 

 which from the "tympanic bone" of the higher Vertebrate has now been so 

 copiously demonstrated. 



t P. Z. S. 1874, pi. xxix. figs. 1 and 2. 



