or THE SKULL IN THE UKODELOUS AMPHIBIA. 
541 
The apex of the pier is thick, its upper part (seen in the figure) is the “ ascending 
process ” ; the lower spur or “ pedicle ” is not seen in this view. But from the apex 
the elbowed part is seen embracing the outer face of the auditory capsule ( au .). 
This part is the rudiment of the otic process. It is now, as to this process, quite 
like a newly metamorphosed Frog or Toad (see “ Skull of Batrachia,” part 2, plate 55. 
fig. 6). 
The notch on the hinder edge of the quadrate cartilage (mandibular pier) exactly 
corresponds with the concavity for the condyle of the hyoid cornu of a tadpole ; but its 
position under the ear is attained very late by the Batrachia. In their larva this point 
is beneath the eye (“Frog’s Skull,” plate 5. fig. 1, liy.). 
In an extremely short time the mandible has doubled its relative length (figs. 1 & 3, 
mk.), and from terete it has become flat and steep ; it is turned down in front, and the 
mass of elevated cells seen in fig. 2 have developed into a “ splenial ” bone and teeth 
(sj).). Moreover the two rami meet at the chin. 
The segmentation of the other five rods is now evident, and no other subdivision will 
appear. The Urodeles divide these arches more than the Batrachia, but far less than 
fishes (Elasmobranchs especially). There is no segment in any of these answering to 
the apex of the quadrate or mandibular pier, which in the Skate is distinct, and may 
be a serial homologue of the , “ pharyngo-branchials ” of fishes ; but in some Batrachia, 
such a segment appears, sooner, or later, in the hyoid region. 
But in this, and in nearly every kind of Urodele, a joint appears near the lower end 
of the hyoid cornu, the “ hypo-hyal.” It exists in the Bay ( Raia clavata ), but not in 
the Dogfish (Scy Uium canicula), and is present in Osseous Fishes, where it receives two 
osseous, centres. In these, and in the Sturgeon, it is segmented off (M. Micr. Journ. 
June 1873, plate 20. fig. 1, h.hy.), and not indicated merely by a separate bony 
deposit. 
The rest of the hyoid is a flattish bar, gently arcuate, and having now its apex filling 
in the notch of the quadrate. This apex is the serial homologue of the “ angular pro- 
cess ”, of Meckel’s cartilage ( mk .). There is no basihyal in these types ; but the hypo- 
hyal becomes attached to the fore end of the first basibranchial, a part not yet 
chondrified perfectly. 
But the next two arches (1st and 2nd branchials) segment themselves higher up. 
They have no lower segment or hypo-branchial, so constant in Elasmobranchs, Tele- 
ostei, &c., nor does the apex of the arch become detached as a pharyngo-branchial, as 
in fishes. The longer, upper segment is here the “ epibranchial,” and the lower, shorter 
piece the “ cerato-branchial”*. 
The 3rd and the 4th (or empty arch, e.br. 4) are undivided. These are very small 
rods. 
* As we were working at the same types, Professor Huxley and I agreed that this was the proper nomen- 
clature of these segments, which are so named in his invaluable memoir on MenobrancJius (P. Z. S., Mar. 17, 
1874). 
