194 B. NATURAL HISTORY. 
Il. ZOOLOGY. 
1. On THe Homotocies or some oF THE CrantaL Bones OF 
- = 
THE REPTitia, AND ON THE SysTEMATIC ARRANGEMENT OF 
THE Crass. By Epwarp D. Cops, of Philadelphia, Penn. 
Tur great group of Reptilia may be considered as well circum- 
scribed by the characters presented by their skeletal strutcure. 
They may be defined as vertebrates, with mandibular arch sus- 
pended from the cranium by the intervention of an os quadratum, 
or extra-auricular malleus; with the basis of the cranium formed of 
the cartilage bones, basisphenoid, sphenoid, and usually presphe- 
noid; with a coracoid bone; and with metatarsals, metacarpals, 
second row (and usually first row) of tarsal and carpal bones dis- 
tinct, and not coésified. 
Within these limits there exists perhaps a greater variety of 
structure, in other respects, than in any other vertebrate class. 
The homologizing of the elements which present this variety is 
therefore a point not attainable without much study, while the 
homologizing of the same with their representatives in other 
classes is still more difficult. In the present essay a few points of 
this nature are, it is hoped, elucidated, especially with reference to 
the structures of the crania in the orders Ichthyopterygia and 
Anomodontia, Finally, the bearing of these and other points on 
the systematic arrangement of the class are alluded to. 
1. Homologies and Composition of the Cranial Arches. 
The bony arches which connect the facial part of the cranium 
with the posterior part of the brain-case, in nearly all Vertebrates, 
are primarily only two in number; viz, the zygomatic and the 
quadratojugal. They, however, form connections with each other 
and adjoining portions of the cranium, so as to complicate their 
determination, which is increased when one or other of their usual 
connections is, under these circumstances, atrophied or omitted. 
The zygomatic arch takes its name from the only one which is 
‘present in the Mammalia; and that arch which is homologous with 
it throughout lower vertebrata must retain the name. It is then 
the arch connecting the maxillary with the squamosal. (or squamo- 
sal part of the temporal) bone, and is therefore composed in large 
part of the malar. 
