168 
MR. W. K, PARKER ON THE STRUCTURE AND 
The tegmen tympani is showing itself, and outside the 'parachordal floor the 
oblique fenestra ovalis is nearly filled with the oval stapes ( st .), now well chondrified. 
The unfilled fore end of the fenestra ovalis is waiting until after most of the meta¬ 
morphosis is done to receive the columella, which will articulate with the newer 
parachordal floor at its outer edge. Cartilage has spread from the tegmen tympani 
into the angular space between the capsule and the otic process of the suspensorium 
(ot.p.), just as cartilage spreads from the inner edge of the capsule into the mem¬ 
branous superoccipital tract—for cart day e, like hone, in many instances, does not heed 
morphological landmarks. The little cordiate cartilage (fig. 7, sp.c.) which is develop¬ 
ing in the opercular membrane, over the 1st cleft, becomes free from the ear-capsule, 
coalesces with the otic process of the suspensorium, becomes detached again from that 
part, and then develops into the annulus tympanicus, and is permanently kept as the 
cartilaginous “ operculum ” of the cleft to which it belongs; the specialisation of both 
cleft and operculum failing to disturb the original morphological relation of the parts. 
In like manner the modified hyo-mandibular or columella, will be wedged in between 
the auditory capsule and the basal plate, exactly as in its simple and generalised 
counterpart in the Selachians. 
The suspensorial arch has tire normal form ; the pedicle (fig. 7, inside sp.c.) is 
narrow, the otic process (fig. 6, ot.p.) is a thick crest, ascending from the main bar as it 
suddenly turns inwards to become the pedicle. The quadrate condyle is a small 
trochlea, and looks inwards as well as forwards, and the terminal or quadrate region 
(q.) is altogether oblique ; it sends inwards an angular pre-palatine spur which is 
attached to the cornu trabeculae in front of the narial passage (i.n.) by a ligament. 
The orbitar process (fig. 6, or.p.) is large and rounded, with raised edges; the 
hyoidean condyle beneath it has the usual reniform outline, and is scooped. The 
wings of the ethmoid are very rudimentary at present, and I find no post-palatine 
rudiment outside them. The mandibles (fig. 7, mk.) are short, thick, ulniform rods, 
with the usual hooked angular process ; they are articulated to the lower labials by a 
wide surface ; these latter are each half a thick crescent with a raised lip. The 
temporary upper labials ( u.l .) are large, thin, crescentic flaps fitted on to the end of 
the cornua trabeculae. The hyoid bar (fig. 7, c.hy.) has the usual form; it has a large 
condyle and an unciform stylo-hyal free end; it has a narrow waist, obliquely ridged, 
externally, for muscular attachment, and then expands largely, most on its hinder 
margin, to contract again where it is joined to its fellow, ventrally, by the square, soft- 
celled, basi-hyal. The branchial arches were not figured in this instance, they were 
quite normal. 
The parasphenoid (fig. 7, pa.s.) formed a floor, very exactly, to the newer cartilage 
of the intertrabecular space ; it had, although it was very thin and young, developed 
the rudiment of its lateral and posterior angles; the last was directly under the 
(endoskeletal) bony sheath of the notochord. 
