No. 3.] VERTEBRATE-SKULL. 469 
we may state the following: There are always to be found three 
elements in connection with the ear, the paroccipital, petrosal, 
and stapes; the stapes, very large in the lower types (/chthy- 
osaurus) becomes more and more reduced in size, ascending to 
the higher types. A fourth element, the supraoccipital, takes 
part in the Monocondylia, but not in the Mammals. 
Passing now to the examination of the lower forms (Vecturus, 
Mastodonsaurus, Amia, and Lepidosteus), in Necturus the fora- 
men magnum is bound by the small exoccipitals; on the outer 
side of these are the free paroccipitals, then follow in front the 
large stapes and the petrosal. The same condition can be seen 
in Proteus, the other living representative of the Proteida; but 
in the other Batrachia the paroccipitals are co-ossified with the 
exoccipitals. 
In the Stegocephalia! we have exactly the same: in some of 
the genera (Cyclotosaurus) the paroccipital is free from the exoc- 
cipital; in others (Mastodonsaurus) it is co-ossified with the 
exoccipital. The paroccipital is in relation to a dermal plate, 
which is very improperly called the “epiotic.”’ I propose the 
name “ pavoccipital plate’ for it. 
Turning now to Amza,* we find the exoccipitals very large; 
on the upper and outer side of these a small bone is seen, which 
corresponds exactly to the paroccipital in Cyclotosaurus ; it is 
also in relation to a dermal plate, and there is no doubt that 
this small bone is the true homologue of the paroccipital in the 
Batrachia and higher Vertebrates. Between the extensive 
petrosal and the exoccipital a large but thin bone is found, the 
“amtercalare”’ of Vrolik. ‘ 
In Lefidosteus the conditions are about the same, but there 
is no bone between the petrosal and exoccipital, corresponding 
to the intercalare. If this bone is removed in Ammza, we have 
the arrangement of Lefzdosteus. In Amza the paroccipitals 
take no part in the formation of the semicircular canals, but 
they do in Lefpidosteus. 
1 It is to be regretted that my friend, Dr. E. Fraas, did not give much attention to 
morphological questions in his extensive work on the Labyrinthodontia of the Trias, 
for which he had a wonderful material at hand; my determinations are mostly based 
on his text and figures. 
2 My thanks are due to Prof. Ramsay Wright of Toronto for a splendid specimen 
of Amia, presented for examination. 
