130 MR. W. K. PARKER ON THE STRUCTURE 



Owl (fig. 5), in two pouting lips; they underlie the common Eustachian opening (eu); 

 outside and in front of this emargination the basipterygoids (bpg) are seen projecting 

 from those wings of the parasphenoid that form the " anterior tympanic recess." The 

 narrowed part of the parasphenoid (pas) is relatively slender, and the pterygo-palatine 

 bones undergird it for most of its extent. The great anterior palatine interspace is large, 

 but it is lessened in the dry skull by an ossification which has affected the retral part of 

 the trabeculse and alee nasi (fig. 3, aln). A similar bony bridge is formed in Sarco- 

 ramphus papa by the maxillo-palatines where they join the nasal septum. 



Most of the nasal capsule, as in pluvialine and gallinaceous birds, is unossified. The 

 vomer (fig. 3, v) is of a type rare in birds ; it is thoroughly Chelonian, more so than in 

 any other bird save the Falcon (fig. 4, v), although some approach is made to this in the 

 Sacred Ibis and the Tree-Duck (Dendrocygna). 



As in the other Raptores, it is truly azygous, so also it is in the Gallinacese ; but in the 

 Cranes and all pluvialine birds it is composed of long lathy pieces, that converge and 

 ankylose, only keeping apart behind. 



In the Chelonia the azygous knife-shaped vomer spreads out behind and above to 

 articulate with the orbital plates of the palatines, whilst in front it descends and helps 

 the maxillaries to form an anterior hard palate. Just so does this bone behave in the 

 Falcon and Cariama. In the Green Turtle ( Ghelone midas), however, the palatines have 

 a small palatine lamina joining this fore foot of the vomer ; this part is arrested in the 

 Cariama and the Falcon (figs. 3 & 4, prpa'). In a side view the vomer of the Cariama 

 (fig. 3", v) is seen to be very high in the middle, low and flat in front, and gradually to 

 lessen behind ; the middle part is deficient of bone for a large space. This vomerine 

 fenestra is repeated in the large Falcons (Plate XXV. fig. 12). The articulation of 

 the vomer with the ascending or orbital plates of the palatines is through the medium 

 of the keystone-piece of that arch, the medio-palatine (mpa). This bone is of great 

 interest ; hitherto I have only found it in Birds, and amongst them most developed in 

 Woodpeckers (Trans. Linn. Soc. ser. 2, Plate II. p. 9). But it has just been shown to 

 exist very commonly in Cuculine types. 



There is no abrupt line of demarkation between this ossicle and the paired meso- 

 pterygoids ; and all the gradations are seen in the Raptores, where these intercalary 

 pieces are very variously developed. In the Cariama it is a roughish wedge of bone, 

 rounded behind, pointed in front, and wedged in between the right and left ethmo- 

 palatines laterally ; vertically is jammed in between the parasphenoid and vomer. There 

 is one ossicle here in the young of Falco tinnunculus (fig. 4, mspg) ; but this is the 

 apex of a right mesopterygoid, the left being suppressed. In Sarcoramphus (fig. 19) 

 it is more truly azygous ; in Neophron (Plate XXV. figs. 14 & 15) it is a notable right 

 mesopterygoid; but in that bird the mesopterygoid appears at both ends of its region 

 (fig. 16), a little grain of bone occurring at the junction of the pterygoid on the 

 same side. 



In Helotarsus ecaudatus there is one small bone (a right mesopterygoid) in front 

 (Plate XXV. fig. 9, mspg) ; but certain Owls (Stria; stridula, Plate XXV. fig. 20, and 



