STUDIES OF THE MACRO CH IRES . 
311 
The interorbital septum, in the specimen of Ampelis before 
me, is entire, although encroached upon above and behind by 
the great deficiency or vacuity in that part of the brain-case from 
which the first pair of nerves make their exit. The foramen for 
the exit of the second pair is no larger here than the size of the 
nerve demands. In HesperocicMa both of these foramina are 
considerably larger than is required for the passage of the 
nerves, while in addition a vacuity occurs in the interorbital 
septum of the Thrush. 
Among the higher types of Thrushes, as in the one just re- 
ferred to, the bony entrance to the ear looks directly forwards, 
while in the Tyrannidce this aperture looks downwards, forwards, 
and outwards; in the case of Ampelis it is more as we find it in 
HesperocicMa, and in both of these latter forms a conspicuous 
shell-like covering of bone is developed from behind forwards, 
which protects this important orifice. 
In all the true Passerine birds that I have examined a quad- 
rate bone has a well-pronounced orbital process ; two facets 
upon its mandibular foot, the outer being placed transversely, 
the inner obliquely ; while the long diameter of its mastoidal 
head is also transverse, and supports two articular facets in 
Ampelis and the Oscines, which facets in the Tyrannidce almost 
completely merge into one. 
Turning now to the under view of the skull as shown in PI. XVII. 
fig. 6, we observe that the anterior extremities of the palatines 
(pi.) are very slender and wide apart. I have already pointed 
out how the space between them beneath the superior osseous 
mandible is filled in by a plate of bone in the Tyrannidce . The 
postero-external angles of the palatines in Ampelis are rounded 
and projecting, much as we find them in some Swallows, and 
not very unlike the form they assume in some Swifts. 
In this Chatterer the hinder portions of the palatines are 
considerably extended laterally, and lie principally in the hori- 
zontal plane ; whereas in such a bird as HesperocicMa they are 
less noticeable for this, while on the other hand their internal and 
external “ laminae ” are better developed in this Thrush. 
So far as I have examined, in all Passerine birds these bones 
meet for nearly the entire length down the middle line to the 
articulation of the pterygoidal heads, and only diverge slightly 
in front to meet the backward-extending forks of the vomer. 
