DEVELOPMENT OE THE SKULL IN THE BATEACHIA. 
611 
the adult only figured the upper part ; that which corresponds to the whole of the hyoid 
of the Urodela (Huxley, “ On Menobranchus ,” plates xxix., xxx., hy .) has its apex only 
figured. 
Iu the Batrachia there is an antero-superior rod intimately connected with the 
stapes ” ( st .) ; but in most Batrachia (not in Pipa) it is late in its development. The 
antero-superior palatine and the fore-turned part of the mandibular arch are also late ; 
and both in Teleostei and Ganoidei amongst the Fishes, and in all the air-breathing 
Vertebrata, this region, the “ pterygo-palatine arcade,” is behindhand in growth, and 
suffers an extraordinary amount of metamorphosis. The mandibular is, as it were, a 
double arch. 
So also is the hyoid an arch, which becomes subdivided into, or develops separately, 
in an untimely manner , two distinct and very dissimilar facial arches. 
Its morphology is very varied in different groups ; in the Shark the segment called 
hyomandibular forms a hinge with the distal part or stylo-cerato-hyal ; they are related 
like a rib and sternal rib, or like the quadrate and the free mandible. 
But that change in the disposition of parts which suggested to Professor Huxley 
the term hyomandibular is seen in the Skate, in the early embryo of which the hyoid 
arch is seen to chondrify into, (1) an antero-superior segment, broad above and having 
a round point below, which lesser end is tilted upwards and forwards, and is strongly 
articulated to the pier of the mandible ; and (2) the proper, gill-bearing hyoid arch, 
which is separately attached to the skull. 
In the Salmon it is otherwise (see “ Salmon’s Skull,” plates i. & ii.) ; for in that type 
the hyoid chondrifies as one bar on each side, which splits almost from top to bottom 
(a little obliquely), and then the anterior segment becomes changed in form, tilted, and 
articulated with the inner face of the quadrate, to form the characteristic hyomandibular 
swing. The hinder piece, and a short segment from below, becomes the proper functional 
hyoid arch, and is swung by a secondary (“ interhyal ”) bone from the antero-superior 
piece, just within its middle part. It is perfectly plain that the hinder piece in the 
Osseous Fish, and the short distal segment, the “ hypo-hyal,” correspond to the long 
and short pieces of the hyoid arch of Menobranchus ( op . cit. plates xxix. & xxx., Hy, Hh , 
and ch.), and also to the undivided, low-hung hyoid of the larval Batrachian (Plate 55, 
and infra). The gradual ascent of that bar and its change of form was traced in my 
paper on the Frog ; in that type it ultimately articulates with the antero-inferior ridge 
of the auditory mass, below and in front of the fenestra ovalis and stapes. In the 
common Toad (Plate 54. figs. 4 & 7, st.h) it is thoroughly fused with the periotic car- 
tilage at the same point. In the figure just referred to the tegmen tympani is cut away 
to expose the facial attachments, and above the massive stapes (st.) there is seen a partly 
ossified bar having, on the whole, the same relation to the cerato-hyal that the upper 
tilted segment has in the Skate. 
In that type this part is not ossified, but in Osseous Fishes it acquires two ectosteal 
sheaths, and becomes two bones, united by synchondrosis (“ Salmon’s Skull,” plates v. & vi. 
4 Q 2 
