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 hemal 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 thyroidiennes’ of Cuvier and Dugés) 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 (as, 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 (ao, 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’ (7b. 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 (48) 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 (46) diverge and include the larynx in their fork ; and support at their 
extremities a bony or gristly (cerato-branchial) style (a7). 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 inserted, by way of rare exception 
_ in that bird, into the right nostril. 
- * Dugés appears to have first pointed out this error, but without, however, perceiving the 
true homology of his ‘ cornes thyroidiens’ with the hypobranchials of fishes. 
