612 
ME. W. K. PARKER ON THE STRUCTURE AND 
h.m., sy.). The specialization in the Toad is in one respect different from what we see 
in the Fish ; for the distal end of the bar in the former passes outside the quadrate, and 
in the latter on the inside. But both inside and outside are secondary relations altogether, 
as may be seen in the position of these parts in embryo Teleostei and in the Sturgeon, 
where the lower segment of the antero-superior piece is simply placed behind the quadrate 
(see 4 Monthly Microscopic Journal,’ June 1, 1873, plate xx. fig. 1, sy ., q.). In the Frog 
and Bull-frog the antero-superior bar is in two segments, as in the Sturgeon ; in the 
Toads ( Bufo and the 44 Aglossa ”) the bar is ossified as a larger proximal and a smaller 
distal bony rod, without segmentation of the intervening cartilage. Also, in the 
young of all, and in most Teleostean fishes, the head of the hyomandibular is unossified, 
and the foot or distal part of the “ symplectic ” or terminal piece. Moreover, Professor 
Huxley, who has shown me the great difficulties here to be encountered in the inter- 
pretation of the parts, knows full well that the portio dura nerve passes over the colu- 
mella of the Toad and the hyomandibular of the Fish alike. One more remark : if the 
parts here taken to be the hyomandibular and symplectic, although modified to form 
the curious auditory “ columella,” are not developed at the same time as the hyoid bar, 
neither are they contemporaneous with the stapes, into which category Professor Huxley 
seems inclined to place them. Further evidence will turn up in the embryo of the 
common Toad, and also in the development of the “Aglossa” {infra) ; to my own mind 
the stapes is a new thing in the Amphibia, not existing in the Fishes ; and when an 
antero-superior bar is developed, as in the Batrachia, its upper segment is the hyo- 
mandibular, and its lower the symplectic, whatever names these parts may receive on 
account of their auditory modifications'*. In this, as in other Toads, the columella is a 
very elegant structure (Plate 54. figs. 7 & 8) ; its parts take their names from their sta- 
pedial (auditory) relations. As in the Frog, the fenestra ovalis is a window lying in a 
deep recess of the side wall of the ear mass ; that recess is mainly filled by the irre- 
gularly oval, lenticular stapes, whose flat face is applied to the fenestra, whilst the 
convex face looks outwards. 
The proximal part of the columella is shaped like a planting- 44 dibble,” but the conical 
end is all soft, and the ensheathing bony shaft narrows and twists itself as it runs 
forward (fig. 8, it.st.). The rounded face of the subconical part fits against a shallow 
notch on the antero-superior edge of the stapes, and its inner face lies in the recess. 
Considered as a segment this answers to the short 44 interstapedial ” of the Frog {op. cit. 
plate viii. fig. 9, it.st.). 
But that which forms the main bar in the Frog, the 44 medio-stapedial,” is here one 
fourth only the length of the proximal piece, and is a very small cylindrical bone. The 
two bones fit close together, and the end piece leaves much cartilage unossified — a soft- 
ended 44 symplectic.” The soft part bends at right angles upon the little “medio-sta- 
* It cannot be an unmeaning fact that, whilst the Erogs subdivide their columella into two segments of 
cartilage, as in the Sturgeon, the Toads should have theirs marked off into two parts by two separate bony rods, 
as in the Osseous Fishes. 
