ON THE VERTEBRATE SKELETON. 239 



the coalescence of their cartilaginous bases with the basihyal, the expansion 

 of the basihyal and extension of its anterior and external angles ; in front of 

 which the now long and slender ceratohyals usually coalesce with the basi- 

 hyal ; their opposite ends having shifted their attachments and retrograded, 

 like other haemal arches of the skull, in the course of the metamorphosis. 

 In the case of the hyoid arch of the frog, the change of place is from the 

 tympanic pedicle backwards to the persistent cartilaginous petrosal : and 

 this is a very suggestive and significant change. All the parts of the hyoid 

 remain cartilaginous except the appended and persistent detachments from 

 the visceral system of the branchial arches: these long ' hypobranchials' 

 (' cornes thyro'idiennes' of Cuvier and Duges) diverge and include the larynx 

 in their fork. The relative position, connexions and office in subserviency 

 to the larynx, to which the retained parts of the splanchno-branchial arches 

 are introduced in the lowest of the air-breathing vertebrates, are preserved in 

 all the higher classes. The ' hypobranchials' are as constant in their ex- 

 istence, therefore, as the upper larynx itself, and attach themselves more 

 especially to the thyroid element of that larynx. We recognise them by this 

 relation in birds and man (40, figs. 23 and 25), where they always much ex- 

 ceed the parts of the true hyoid arch (cerato- and epi-hyals) in length ; and 

 in birds, where these elements (40, fig. 23) are sometimes obsolete and always 

 rudimental, the hypobranchials have been mistaken by both Cuvier and 

 Geoffroy* for the ceratohyals or anterior cornua. 



For the modifications and special homologies of the complex hyoid appa- 

 ratus in lizards, I refer to my ' Lectures on the Vertebrata.' The crocodiles 

 offer a well-marked ordinal difference from those inferior sauria in this as 

 in most other parts of their structure. The basihyal and thyrohyals have 

 coalesced to form a broad cartilaginous plate, the anterior border rising like a 

 valve to close the fauces, and the posterior angles extending beyond and sus- 

 taining the thyroid and other parts of the larynx. A long bony ' ceratohyal' 

 (fig. 22, 40), and a commonly cartilaginous 'epihyal' (ib. 39), are suspended 

 by a ligamentous 'stylohyal' to the paroccipital process ; the whole arch 

 having, like the mandibular one, retrograded from the connection it presents 

 in fishes. 



"in birds as in chelonians, the ceratohyals are much reduced, and the chief 

 'cornua' of the hyoid are represented by the hypo- and epi-branchials (thy- 

 rohyals), which here attain their maximum of length and tenuity. The basi- 

 hyal (fig. 23, 41), as in Chelys, is long and slender, but is always a simple 

 piece ; and, as in lizards, is usually most expanded posteriorly, from which 

 expansion the thyrohyals (40) are sent off. Conforming with the long and 

 slender tongue in most birds, the basihyal extends forwards, and is articu- 

 lated with the rudimental ceratohyals (40), when these exist, at some distance 

 from the thyrohyals. A commonly long and slender, sometimes spatulate 

 glossohyal (42), is articulated to the fore-part of the basihyal ; and a con- 

 stantly long, slender and pointed urohyal (43) is articulated with the posterior 

 end of the basihyal, and extends backwards beneath the trachea. The thyro- 

 hyals (40) diverge and include the larynx in their fork ; and support at their 

 extremities a bony or gristly (cerato-branchial) style (47). This is never 

 attached by ligament to the base of the skull, but is suspended freely, as in 

 the chelonia, by the glossohyoid and omohyoid muscles ; it, however, curves 

 over the back and upper part of the cranium in the woodpeckers, and the 

 extremities of both cerato-branchials are iuserted, by way of rare exception 

 in that bird, into the right nostril. 



* Duges appears to have first pointed out this error, but without, however, perceiving the 

 true homology of his ' cornes thyro'idiens' with the hypobranchials of fishes. 



