1902.] OSTEOLOGY OP THE PALCONIFORMES. 281 



in the collection of the British Museum the left process is smaller 

 than the right, and both almost fail of their purpose, not only 

 in this species but throughout the genus. They present within 

 the Order every degree of degeneration, from the prominent pillars 

 of Serpentarius to the most minute prickles. 



Traces of the anterior basicranial font^nelle are often present. 



The Lateral Surface of the Cranium. (Plate XXXIII. figs. 1-8.) 



The tympanic cavity attains its greatest size in the Falcons. 

 It may be studied in its more primitive form in such examples 

 as Polyhoroides, Fandion, Pernis, and the Vultures. The lateral 

 occipital wings which bound this cavity behind in Polyhoroides 

 are but feebly developed. The fi'ee border, on either side, 

 terminates in a blunt and low prominence behind and slightly 

 above the level of the processus zygomaticus, and marks at the 

 same time the lower and hindmost extent of the temporal fossa. 

 In Pandion the free border of this wing, which is still feebly 

 developed, slopes obliquely backwards and vip wards to the level 

 of the processus ai'ticularis squamosum, then turns sharply 

 forwards to terminate in the process itself. Pernis resembles 

 Pandion in this respect, but neither the backward slope nor the 

 forward angle is so marked. In Serjjentariiis and the Vultures, 

 e. g. Neophron., Gypohierax, and Qypaetus, the free edge of this 

 wing is of greater extent, and projects as a slightly raised ridge 

 beyond the zygomatic process. [In Gyps the form of the lateral 

 occipital wing is drawn backwards and downwards to terminate 

 in a prominent processus ala3 exoccipitalis inferior (paroccipital 

 process), and thus in this respect differs from Neophron, where 

 the wing is more feebly developed and slopes from before back- 

 wards and upwards.] In Buteo the ridge laterad of the zygomatic 

 process is much more prominent. In Haliaetus and Aquila it has 

 increased still more. In the Falcons it forms a thin laminate 

 plate, rising upwards to the level of the base of the zygomatic 

 process of the squamosal, the free edge of which is turned 

 forwards. In the development of this portion of the exoccipital 

 it bears a strong resemblance to the Striges, e. g. Bubo. 



The roof of this cavity is formed by the under surface of the 

 processus zygomaticus squamosi. Its floor, in part by the 

 lateral occipital wing, and in part by the ossification of tissue 

 extending between this wing and the external angles of the basi- 

 temporal plate. In front it is bounded by the quadrate. 



Within this cavity, in the dried skull, are two large apei'tures 

 which may be considered sepai-ately. The first lies near the 

 roof of the cavity and separates the squamosal and otic articular 

 surfaces of the quadrate. The aperture leads vipwards and 

 backwards, so as to form a space between the anterior vertical 

 and horizontal canals of the internal ear and the lateral occipital 

 wing. This is the recessus tympanicus superior — the temporal 

 recess of my earlier papei-s. 



The second and lower aperture is divided from the first by the 

 Proc. Zool. Soc— 1902, Vol. I. No. XIX. 19 



