ZOOLOGY. 195 
The quadratojugal arch, as its name implies, is that which con- 
nects the maxillary with the quadrate bone. As the quadrate 
bone only exists as the malleus within the ear-chamber in the 
Mammalia, it is obvious that it cannot exist in that class. It can 
only be found in the vertebrata, from and including the birds, 
downwards. As the quadratum is projected, below the squamosal, 
the position of this arch is always inferior to that of the zygo- 
matic. It is composed normally of the malar (or jugal) and quad- 
ratojugal. 
A third arch, which is especially characteristic of the Reptilia, 
connects the parietal bone with the superior extremity of the quad- 
rate. The connection is accomplished by the intervention of the 
opisthgtic or squamosal, or both. 
The character of the arches existing in the different types of the 
vertebrata, above the Dipnoi, may be expressed schematically by 
the following table : — 
I. Neither zygomatic nor quadratojugal arches. 
a. Without parieto-quadrate arch. : 
Batrachia Urodela except Pleurodelide ; Ophidia. 
Lacertilia Ophiosauri and Typhlophthalmi. 
Testudinata Chelydide. 
Mammalia Edentata (part). 
aa. With parieto-quadrate arch. 
Lacertilia Nyctisaura. 
Testudinata (Hydromedusa Platemys Rhinemys). 
II. Quadratojugal only. 
a, Without parieto-quadrate arch. 
B. With quadratojugal bone. 
Aves. 
BB. Without quadratojugal bone. 
Batrachia Anura in general. 
IM. Quadratojugal and zygomatic arches present. 
1. No postorbital arch. 
Batrachia Anura (Discoglossus). 
2. A postorbital arch. 
_a, Without postorbital bone. 
Crocodilia. : 
aa, With postorbital bone. 
Batrachia Stegocephali (Apateon). 
Ichthyoptery gia. ; 
Rhynchocephalia (Sphenodon). 
2 Sauropterygia. 
Ornithosauria: 
IV. Zygomatic arch only. 
1. With postorbital arch. 
a. With postorbital bone. 
