578 DE. w. G. EiDEWooT) OX THE nyoiiRAXCiiiAL [May 18, 



enclosed. The lateral foi-amen of the adult skeleton is thus not 

 due to a secondary fenestration in a continuous plate of cartilage 

 as might be supposed, but owes its origin to the closure of a deep 

 notch or sinus. By a similar process of overgrowth of marginal 

 cartilage the hyoglossal sinus (hgs., fig. 9), constant in all tongued 

 Anura, is, in Pclodytes, very nearly converted into a foramen such 

 as occurs in the ^Aglossa. The enclosing cartilages {pa.) are 

 secondary additions to the most anterior parts of the hyoidean 

 cornua (see figs. 8, 7, and 6), and in some specimens actually over- 

 lap one another. The posterior and anterior thirds of the hyo- 

 glossal space are closed by membrane, -while the mid<lle third 

 ti'ansmits the large hyoglossal muscles. 



If we disregard for the momeut the detached parts of the 

 hyoidean cornua, the outline of the hyobranchial skeleton is 

 definitely elliptical in shape, the continuity of tlie ellipse being 

 broken in six places. There is nothing remarkable about the 

 thyrohyals (<, fig. 9) ; they are broadest behind and are narrowest 

 at two thirds of their length from the posterior end. The 

 cartilaginous processes {ppl., fig. 9) running parallel to the thyro- 

 hvals on their external side are more strongly developed than is 

 usual in Phaneroglossa, and their swollen extremities touch the 

 circumscribing eUipse. The deep notches in front of and behind 

 this process are closed by imperforate membrane. 



Oa the ventral surface of the basal plate or body of the hyoid is a 

 curious splint-bone (v, fig. 9), consisting of a short central transverse 

 bar, from the extremities of whieli project a pair of long antero-lateral 

 processes and a pair of short tapering postero-lateral horns. The 

 extremities of the latter extend along the ventral surface of the 

 anterior ends of the thyrohyals. The ossification is partly buried 

 in the hyoglossus muscle, some of the fibres of which pass between 

 the bone and the basal plate. The bone is attached to the rest of 

 the hyobranchial skeleton only by its extremities and is readily dis- 

 sected off. It is not au ossification of the cartilage of the basal 

 plate like the paired and frequently unsymmetrieal ossification 

 of Bombinator, but rather corresponds with the V-shaped ventral 

 bone of Alytes and the paired ossification of Discoi/lossus \ 



There are numerous muscles in relation witli the hyobranchial 

 skeleton of Anura, and, in making a comparative study of this 

 portion of the skeleton in different genera, the evidence which the 

 muscles afford towards the recognition of homologous skeletal 

 parts is not infrequently of the greatest value. It is only in the 

 Frog (Rana) that the muscles of this region of the body have been 

 studied with any degree of precision, and, since the hyobranchial 

 skeleton of this genus is most familiar to anatomists, I have 

 instituted a comparison between the areas of muscle insertion in 

 the hyobranchial skeleton of Pelodytes and Rana. The muscles of 



^ Parker (12. pi. 20. fig. 10) does not show these splint-bones ; but, as he 

 bimself has since admitted (Pliil. Trans. Koy. Soc. vol. 173. 1882 (1883), 

 p. 139), the specimen there figured is one of Hana escideiiia. and not of Binco- 

 fflosstis. 



