406 REPRESENTATIVES OF THE MALLEUS AND THE INCUS. [ May 27, 
In the Chimere, Dipnoi, and all Amphibia, the proximal ends of 
the cartilaginous first and second visceral arches become united 
together, at an early period, into a common plate, in which the 
malleal and incudal elements are not separately distinguishable. In 
the Chimere, Dipnoi, and the lower Amphibia they remain in this 
condition throughout life; but in the higher Amphibia changes of a 
most remarkable kind take place, of which I do not now propose to 
speak, as my friend Mr. Parker is engaged in working out that part 
of the subject. 
Fig. 8. 
I have endeavoured to give visual expression to my interpretation of the 
medifications of the proximal ends of the mandibular and hyoidean arches 
in the series of diagrams A, B, C, D, EH, F, displayed in fig. 8. In all these 
the mandibular arch is shaded with vertical lines, while the hyoidean arch is 
left unshaded or nearly so. The letters have the same signification through- 
out. In the mandibular arch :—Qw. Quadrate. Mn. Mandible or Meckel’s 
cartilage.. In the hyoidean arch :—a. Extrastapedial. 0. Suprastapedial. 
Stp. Stapes. St. Stylo-hyal. Hy. The ventral moiety of the hyoidean 
cornu. A. Sphenodon. B. Crocodile. C. Bird. D. Mammal. E. 
Teleostean fish. F. Shark. 
In D, od stands for the orbiculare; in BE, Mp? is the metapterygoid, and Sy the 
symplectic. 
