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MR. W. K. PARKER OK THE STRUCTURE AND 
Meckel’s cartilage (mlc.) is now well developed as a free segment cut off from the second 
facial (first postoral) arch. 
The auditory capsule {cm.), now a closed pouch of cartilage, has overgrown the top of 
the third arch (3 liy.) ; and the upper part of this arch has applied itself close to the 
antero-inferior face of the sac. It is then free, and then applies itself closely, to beyond 
its middle, to the second arch ; but the diverging lower part has now become segmented 
from the upper, an oblique joint-cavity has been formed, and a small angle of the upper 
part projects below the joint. 
All this is typically ichthyic ; the upper part, closely applied to but not coalesced with 
the auditory sac, is the “ hyo-mandibular ” (Am.) ; the small angular projection below the 
joint is the “ symplectic ” ( sy .); and the free segment is the “hyoid cornu” (“stylo- 
cerato-hyal ”) (Ay.). 
Fig. 14. — In perfect Tadpoles an inch or more in length, the cranial cavity, its trabe- 
cular rests, and the suspensory part of the short Meckelian rod have all undergone great 
relative as well as real elongation. The free outgrowths of the trabeculae (“cornua,” c.tr.) 
now form large unsegmented counterparts of the Meckelian segments of the next arch, 
and behind the commissure they have become united by a thin connective tract, which 
forms the cranial floor. The pterygo-palatine band has not lengthened, so that the 
suspensory portion of the second arch now forms a very acute angle with the basicranial 
axis. It has become largely bowed-out, however, and has thus formed the large “ sub- 
ocular fenestra ” (s.o.f.), an expansion of the true first cleft, or that between the trabecular 
and mandibular bars. 
The connective at the top of the second arch is now long, bows outwards and back- 
wards, and is confluent with the investing mass behind and the trabecular root above. 
The second cleft (first “ postoral ”) has its upper part still very evident in the space 
between the band in front, and the auditory sac and top of the third bar behind. This 
remnant of the second cleft is rounded below ; and thence the rest of the hyo-man- 
dibular (“ infrahyomandibular,” i.Am.) has become completely fused with the arch in 
front ; this region also is greatly elongated, so that the elegant condyle of the “ hyoid 
cornu” (Ay.) is articulated to the lower third of the compound suspensorium, and the 
more mobile parts of the face and mouth are here as far from the ear-sac as in Syn- 
cjnatAus. 
The free hyoid cornu is now of great breadth, but, as in the third stage, it has not 
coalesced below with the basihyal. The “ suprahyomandibular ” region (s.Am.) is now 
relatively much smaller ; it has gained a more external position with regard to the ear- 
sac, with which it has coalesced by a pedate or sub-bifurcate head. The neck is narrow ; 
and below the neck it bulges downwards so as to form an “ opercular process,” a truly 
ichthyic structure. The ear-sac has opened again ; and its own opercular piece, the 
“stapes” (st.), is some distance behind, and more internal than, the head of the hyo- 
mandibular. 
In the fifth stage (fig. 15) the mandibular pier (qu.) has receded from the trabecular 
