238 REPORT— 1846. 
called ‘cerato-branchials.’ It is with these elements of the branchial arches 
in fishes and perennibranchiate batrachians that we are chiefly concerned 
in tracing the homology of the hyoid apparatus in the air-breathing verte- 
brates. With regard to the branchial and pharyngeal arches, which attain 
their full development only in the class of fishes, I regard them as appertain- 
ing to the system of the splanchno-skeleton, or to that category of bones to 
which the heart-bone of the ruminants and the hard jaw-like pieces support- 
ing the teeth of the stomach of the lobster belong. The branchial arches 
are sometimes cartilaginous when the true endo-skeleton is ossified: they are 
never ossified in the perennibranchiate batrachians, and are the first to dis- 
appear in the larve of the caducibranchiate species; and both their place 
and mode of attachment to the skull demonstrate that they have no essential 
homological relation to its endo skeletal segments. 
The hyoid arch or apparatus retains most resemblance to that of fishes in 
the Siren lacertina ; the basihyal is simplified into a single osseous spatu- 
late piece, with the bowl of the spoon anterior, and supporting a broad and 
flat semicircular glossohyal. A strong and thick ceratohyal is articulated 
by means of a small cartilage to the side of the expanded part of the basi- 
hyal, and a cartilaginous epihyal arches backwards from its upper end. A 
cartilaginous urohyal extends from the hind end of the basihyal, and ex- 
pands into a radiated disc, which supports the membranous trachea and the 
simple glottis. One pair of bony ‘hypobranchials’ is articulated to the 
basi-uro-hyal joint and a second pair to the sides of the urohyal: and to the 
upper and outer ends of these are attached four pairs of cartilaginous ‘ cerato- 
branchials. The fimbriated branchiz are attached to the three anterior 
ceratobranchials. 
In the proteus the urohyal is absent, and it is not again developed in any 
batrachian. The long subcylindrical basihyal supports a subcircular carti- 
laginous discoid glossohyal, and at the angle of union the bony ceratohyals 
are sent off. A pair of hypobranchials diverge from the end of the basihyal ; 
to which a second small pair of basibranchials are loosely connected by an 
aponeurosis. These support three ceratobranchials on each side, which are 
bony. 
Ru the newts there is neither a glossohyal nor urohyal, or but a rudiment 
of the latter, to each side of which are articulated two hypobranchials, whose 
distal ends converge on each side to support a single cartilaginous gill-less 
rudiment of a ceratobranchial. The special homologies of all those parts of 
the complex hyoid, rendered more complex by the retention of part of the 
branchial skeleton, are clearly demonstrated by pursuing the metamorphoses 
of the hyo-branchial skeleton in the larve of the anourous batrachians. In 
the full-gilled tadpole a short and simple basihyal supports laterally two 
thick and strong ceratehyals, and posteriorly two short and broad hypo- 
branchials, to which four ceratobranchials are attached: all the parts are 
cartilaginous. The type of this stage is retained in the siren, with the histo- 
logical progress to bone in the hyoid and hypo-branchial pieces. The second 
well-marked stage in the tadpole shows an extension of the external and 
posterior angles of the hypobranchials, with progressive absorption of the 
cartilaginous ceratobranchials. The growth and divergence of the posterior 
angles of the hypobranchials refer to the development of the larynx, now 
commencing, which part they are destined to support. That period may be 
described as the third stage at which the ceratobranchials have disappeared, 
and the posterior angles of the hypobranchials increase in length and assume 
the character of posterior cornua of the os hyoides. The last and adult 
stage shows the ossification of the elongated angles of the hypobranchials, 
