STUDIES OF TKE MACROCHIRES. 



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 Sesperociclila 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^ 

 wliile ill the Tyranuidce this aperture looks downwards, forwards, 

 aud outwards ; in the case of Ampelis it is more as we find it in 

 IlesperocicJila, 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 underviewof the skull as shown inP]. 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-exterual 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 Hesperociclila they are 

 less noticeable for this, while on the other hand their internal and 

 external " lamince " are better developed in this Thrush. 



So far as I have examined, in all Passerine birds these bones 

 meet for nearly the entire length dow^n 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. 



