MAMMAL-LIKE REPTILES. 779 
Micropholis this duct runs forwards completely in the lachrymal 
bone to the posterior end of the septomaxilla, and it appears from 
its mode of development to have been primitively a mere surface- 
groove. 
The squamosal of Deinocephalia is of some interest; in its 
relations to all other bones, particularly those of the otic capsule, 
the quadrate, tabulare, postorbital, and parietal, it agrees exactly 
with the corresponding bone of the more primitive Gorgonopsids, 
which is clearly identical with the squamosal of Diademodon, 
which is clearly homologous with the bone of the same name in 
Mammals. The squamosal of a Deinocephalian is clearly the 
same as the large temporal element in Varanosaurus, having 
similar relations to the paroccipital, postorbital and tabulare, and 
only differing in retaining its primitive connection with the 
pterygoid. As this type retains a small ‘‘supratemporal,” there 
is now no doubt that the squamosal is the outer of the three 
temporal bones in primitive Reptilia. 
The Auditory Arrangements of the Therapsids. 
Of recent years belief in the truth of Reichert’s hypothesis of 
the homologies of the mammalian ossicula auditus has been 
gradually growing, and the fine work of Gaupp has practically 
placed it beyond question. At the same time, Broom, following a 
suggestion of Seeley’s, has shown how in the gradual increase in 
size in the dentary and the decrease of the other elements of the 
jaw and the quadrate, the “carnivorous” Therapsids gradually 
approach the mammalian condition. The same author has pointed 
out that the stapes is articulated with the quadrate in Therapsids 
just as is the stapes of mammals with the incus. Finally, 
following on my own more accurate account of the Therapsid 
jaw, Mr. Palmer has shown the extraordinary similarity in detail 
between the lower jaw (including the dentary, malleus, pre- 
articular, and tympanic) of a mammary foetus of Perameles and 
that of the advanced Cynodont Diademodon. 
The homologies of the various bones being now placed beyond 
dispute by the work of these authors, it is desirable to carry the 
inquiry further and discuss the position and changes of the 
tympanic membrane and other parts of the ear. 
The stapes of Therapsids is in all cases where the condition is 
known articulated with the quadrate. In the following types, 
Cynognathus, Trirachodon, Nythosaurus, Arctognathus, Lyco- 
saurus, Dicynodon, Lystrosaurus, Dicelurodon, Kannemeyeria, 
Mormosaurus, Prigalion, Lamiasaurus, Dimetrodon, Varanosaurus, 
which cover the superorder very fairly, the stapes has actually 
been seen in place; the facet on the quadrate for its distal end is 
shown in very many more forms. 
Quite recently, when discussing the primitive Therapsid Varano- 
saurus, | pointed out that in many ways it greatly recalled the 
Proc. Zoou. Soc.—1914, No, LILI. 53 
