AND DEVELOPMENT OF THE BIRD'S SKULL. 139 



grooves almost invisible. In older birds a small interpalatine spur can be seen, but 

 in tbe young it is not evident. The ethmo-palatines (fig. 7, epa) are very short, and 

 backwardly placed ; they are high, looking obliquely forwards and upwards, and become 

 spongy ; in front they send forwards a fiat half-coiled horn of bone ; this is lost as a 

 separate process in the adult, for it coalesces with the much enlarged vomer, each 

 process adding to the depth of its shelving sides, and leaving a large fossa above, which 

 opens into most exquisite air-cells. 



The palatines are kept apart by a triple wedge, the vomer (») below, and the early- 

 coalesced mesopterygoids (mspg) above. This structure can only be seen in very young 

 birds before they leave the nest. Now the vomer is a smallish spindle ; afterwards it 

 is a large dagger-shaped bone, with a deeply sulcate upper edge. 



The thin fibrous prepalatine bars (fig. 5, prpa) form rests for the huge, ear-shaped, 

 swollen maxillo-palatines (mxp) ; their tip articulates with the inside of the splintery 

 palatine process of the premaxillary (ppx). The dentary part of that bone (dpx) is not 

 strong, and the beak part is hollowed below. The fore end of the ossified septum nasi 

 coalesces with the premaxillary, and thus an extensive bridge is formed over the anterior 

 palatine space and under the external nostrils, the same as, but much more extensive 

 than, that seen in the Cariama (fig. 3, aln), where the ossification is arrested. 



The hollow part of the beak in front of the nostrils has a bony septum between its 

 air-cavities, formed by the premaxillaries themselves (px), and lying in front of and 

 below the true septum nasi. 



A considerable chink, -^ of an inch wide, separates the maxillo-palatines (mxp) ; 

 so that, notwithstanding their great size, these birds are only " indirectly desmognathous." 

 The septum nasi is thoroughly ossified, but not the outer alse. It is of great antero- 

 posterior extent. 



The orbital septum is a thick cushion of soft bone, very much bevelled away below, 

 but running forwards at its upper part ; this arises from the direction taken by the great 

 cranio-facial cleft, which runs forward as well as upward. 



The weak diverging jugal bars are composed of three elements, as in Accipiter (mx, 

 j, qj) ; both the premaxillary and the maxillary have an angular process. 



But these three elements are not all that is to be seen in the jugal bar ; for that addi- 

 tional bone which I have called the postmaxiilary is here present (Plate XXIV. fig. 8, 

 ptmx); it is a smallish oval grain of bone, and can be seen in young birds not long 

 escaped from the nest. In this bird also can be seen an additional bone behind the orbit, 

 the counterpart of the ichthyic postfrontal or " sphenotic." The lacrymal (partly 

 shown in fig. 8, I) is very large and spongy, and does not send out a superorbital process 

 as in the " Diurnse." 



In the Long-horned Owl (Asio otus) the palatines are supplied with a large vomerine 

 keystone (Plate XXV. fig. 10, v). Here the inner part of the palatine arch may have had 

 a single medio-palatine, or a pair of mesopterygoids ; but they are not distinct, although 

 the specimen was a bird of the first summer ; these sutures are early lost in the Barn- 

 Owl ; and the medio-palatine of the adult is often formed of two mesopterygoids in the 

 young. I suspect it is so in this case. 



SECOND SEBIES. — ZOOLOGY, VOL. I. "U 



