170 
ME. W. K. PAEKER ON THE STRUCTURE AND 
ratus, namely the “annulus tympanicus.” The essential element of the middle ear, the 
stapes (st. ), was seen in the fourth stage ; the condyles and opercular process of the hyo- 
mandibular are now being prepared to form an osseo-cartilaginous chain from the “ mem- 
brana tympani” to the stapes. Under these conditions a new nomenclature will be re- 
quired ; and this will be made to depend upon the stapedial relationship of the chain, 
notwithstanding its different morphological origin *. 
I shall now call the lobes of this trifoliate plate of cartilage as follows — namely, the 
antero-superior “ suprastapedial,” the poster o-superior “ medio-stapedial,” and the freed 
opercular process “ extrastapedial (s.st., m.st ., e.st.). 
The stapes (st.) sends no stalk forwards to meet the new 7 elements, but they grow towards 
it ; this will be seen in the next stage. It may be remarked, in passing, that the top- 
most part of the second postoral arch, in becoming free from the periotic capsule, is 
merely reverting to its primordial condition. 
The branchial arches are beginning to be atrophied (Plate VII. fig. 5) ; the cells form- 
ing the pharyngo-branchial spurs ( p.br .) have proliferated into connective tissue ; the 
arches have become very slender ; and the small hypobranchial spur on each side has 
grown into a solid diverging horn (h.br.) ; the whole basi-hyobranchial bar has enlarged 
into a fiat plate of nearly even breadth. 
Eighth Stage. — Young Frogs of the first early summer. 
During the next six or eight weeks (that is, by the commencement of summer) the young 
Prog has become larger by one-half, has acquired much more of its specific character, is 
more elegant in form, and much less like the Toad than in the newly metamorphosed 
condition. 
Similar modifications have taken place in the skeleton, some of which are of the highest 
morphological interest ; this is especially the case with regard to the “ middle ear.” 
The flat plate which was segmented from the top of the second poststomal arch has 
become a narrow ray with two terete branches as bifurcations, one large and the other 
small (compare Plate VII. fig. 12, s.hm., with Plate VII. fig. 13, e.st., s.st., m.st.). The 
free antero-inferior bar is spatulate, flat within, rounded without, a little bent and dilated 
at the end, and serves, like the “ manubrium mallei” of the Mammal, for the tension of 
the membrana tympani, the edges of which are attached to the almost circular cartila- 
ginous opercular. This process, the extrastapedial, is not, however, the representative 
of the “ malleus,” but is the liberated “ opercular pedicle.” The antero-superior lobe 
(Plate VII. fig. 13, s.st.) has now grown into a delicate terete cartilaginous ray, directly 
continuous with the free descending extrastapedial, but much smaller, and occupying 
only one-third of its top where it passes into it ; this is the “ suprastapedial it is 
attached loosely by fibrous tissue to the fore part of the tegmen tympani at the junction 
* These terms are partly from Professor Htjslet’s paper “On the Representatives of the Malleus and the 
Incus of the Mammalia in the other Yertehrata (Zool.Proc. May 27, 1869, pp. 391-407), and are partly terms 
suggested to me by him in conversation. 
