DEVELOPMENT OF THE SKULL OF THE COMMON FROG-. 
189 
region (1 tr.), thus giving rise to an elongated pterygo-palatine (pet-, jpg-), now as long 
as the suspensoriura ; this bar is semisegmented. Meckel’s cartilage (mJc.) has simi- 
larly increased in size ; the orbitar process ( or.jp .) is becoming starved, and is changing 
an anteorbital for a postorbital position ; and the connective of the second arch is not so 
far from the front of the ear-sac. 
But the most interesting changes are taking place in the third, or “ second postoral 
arch.” The “ suprahyomandibular ” ( s.h.m .) has become nearly free; and the “infra- 
hyomandibular ” ( i.hn .) has grown upwards into a large leafy lohe, which turns its 
convex side somewhat inwards. Moreover the whole upper region is only half as long 
as in the last stage, so that the free hyoid cornu is so much nearer to the skull ; it is 
also much narrower in form. 
The “ symplectic ” rudiment ( sy .) has grown down the posterior edge of the much 
elongated quadrate region, and is partially segmented from it. 
In the 6th stage (fig. 16), Tadpoles with stumpy tails, Meckel’s cartilages and the 
pterygo-palatine bars (ink., pa.pg.) are both longer than the suspensorium, on the front 
face of which, near the top, is seen the remains of the “ orbitar process ” ( or .]).). The 
elongating hyoid cornu (Ivy.) is becoming detached from its fossa, the joint-cavity dege- 
nerating into a mere loose ligamentous union. The “ infrahyomandibular ” [i.hn.) has 
its free lobular edge still higher up; and the starved “suprahyomandibular” ( s.hm .) 
has become a free trifoliate plate of cartilage. It has now lost its ichthyic character, 
and is becoming functionally related to the stapes (st.) as part of the middle ear; and its 
lobes can now be identified with the processes of cartilage which are connected with the 
stapes in the “ Sauropsida.” The antero-superior lobe is the “ suprastapedial,” the pos- 
tero-superior is the “ medio-stapedial,” and the free process, which grows downwards and 
forwards , is the “ extrastapedial ;” the whole piece is now detached from the auditory 
capsule above, and it is still some distance in front of the stapes. 
Seventh Stage (fig. 17). — This is when the little Frogs have nearly lost tire tail-stump ; 
a cartilaginous “ annulus tympanicus ” can now be seen. There is not much difference 
between this stage and the last in many respects ; but the “ hyoid cornu ” (liy.) has 
become very long and narrow, is quite loosened from its original attachment, and is 
gaining a new one above. In the sixth stage the palatine ( pa .) was bending forwards; 
it is now pointed in front ; in both the “ trabecular horns” are almost entirely involved 
in the nasal labyrinth. 
Eighth Stage (fig. 18). — In Frogs taken a month or two later, the pterygo-palatine and 
Meckel’s cartilage (pa.pg., mJc.) are still more elongated, and the relatively shortened 
suspensorium (gu.) forms a right angle with the basicranial axis. The metapterygoid 
root clings more closely to the periotic cartilage ; and the “ infrahyomandibular ” ( i.hm .), 
relatively smaller, is acquiring a more inward position. The narrowing hyoid bar is now 
quite loosened from its old attachment, and is very near to the opisthotic region. The 
detached “ suprahyomandibular ” has now undergone a more perfect metamorphosis 
than can be seen in either Lizard, Crocodile, or Bird. The anterior head has become a 
