THE SKL'LL OF OSSEOUS FISHES. 115 



the arch, stylo-hyal (pleurapophysis, in part, of the mesencephalic 

 vertebra, fig. 30. 38) is a slender styliform bone, which is attached 

 at the upper end by ligament to the inner side of the epi-tympanic, 

 close to its junction with the meso-tympanic, and at the lower end to 

 the apex of a triangular plate of bone, which forms the upper portion 

 of the great cornu, or haemapophysial part of the arch. I apply to 

 this second piece, which is pretty constant in fishes, the name of epi- 

 hyal {lb. 39) : the third longer and stronger piece is the cerato- 

 hyal {lb. 40). 



The keystone or body of the inverted hyoid arch is formed by two 

 small sub-cubical bones on each side, the basi-Jiyals (ib. 4i). These 

 complete the bony arch in some fishes : in most others there is a 

 median styliform ossicle, extended forwards from the basi-hyal sym- 

 physis into the substance of the tongue, called the glosso-hyal (ib. 42), 

 or 'os linguale;' and another symmetrical, but usually triangular, 

 flattened bone, which expands as it extends backwards, in the middle 

 line, from the basi-hyals ; this is the uro-hyal {ib. 43). It is con- 

 nected with the symphysis of the coracoids, wliich closes below the 

 fourth of the cranial inverted arches, and it thus forms the isthmus 

 which separates below the two branchial apertures. In the Conger 

 the hyoidean arch is simplified by the persistent ligamentous state of 

 the stylo-hyal, and by the confluence of the basi-hyals with the 

 cerato-hyals : a long glosso-hyal is articulated to the upper part of 

 the ligamentous symphysis, and a long compressed uro-hyal to the 

 under part of the same junction of the hyoid arch. The glosso-hyal 

 is wanting in the Murcenophis. 



The Diverging Appendage of the hyoidean arch retains the form 

 of simple, elongated, slender, slightly curved rays, articulated to de- 

 pressions in the outer and posterior margins of the epi- and cerato- 

 hyals : they are called ' branchiostegals,' or gill-cover rays, because 

 they support the membrane which closes externally the branchial 

 chamber. The number of these rays varies, and their presence is 

 not' constant even in the bony fishes : there are but three broad and 

 flat rays in the Carp ; whilst the clupeoid Elops has more than 

 thirty rays in each gill-cover : the most common number is seven, as 

 in the Cod {fig. 30. 44). They are of enormous length in the Angler, 



adds a dotted outline of it to complete his Vertebra occipitalis, in xxxviir. tab. xii. 

 Jiff. 32. B I. He had not been prepared by the normal position of the true haemal 

 arch of the occiput in fishes, and by the example of tlic extreme displacement to 

 which a hsemal arch and its appendages may be subject, as in the case of the pelvis 

 and pelvic fin in fishes, to recognise the true hajmapophyscs of the occiput in the 

 dis])laced scapular arch. Bojanus considered the " pterygoids" as the ribs (cos/a) 

 of the parietal .vertebra {ib. p. G4.). 



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