406 Annals of the Carnegie Museum. 



Among the points that have always attracted the most attention in 

 tlie skeleton of the Psiffaci, the cranio-facial hinge is here in Coniinis 

 as perfect in its mechanism as we perhaps will find it in any of 

 the suborder. 



Its structure is too well known to enter \\\)0\\ its details here ; I 

 find, howe\er, that neither in this parrot nor any other of the group 

 that I have ever examined is this feature one whit better developed 

 than it is in Siila hassana. 



Passing now to other parts, we find the union between the sphenotic 

 process and the descending portion of the lacrymal bone to be com- 

 plete, forming an external orbital periphery or ring, which is very 

 nearly circular (Plate I, Fig. i). According to Parker, as I have 

 already said, this is brought about through the intervention of the os 

 iinciiiatiiiu, which in some parrots, by union with the zygomatic proc- 

 ess of the s([uamosal, l)ridges over the temporal fossa. 



The lacrymal itself has indistinguishably, so far as a suture is con- 

 cerned, merged above with the frontal bone, while its imion with the 

 sphenotic process, just alluded to, is ec^ually well obliterated. Inter- 

 nally it unites in a similar manner with the ?,vc\?iS\. pars plana, a circular 

 foramen for the olfactory nerve passing between it and the ethmoid, 

 while externally the antero-inferior arc of the orbital ring is marked 

 by a longitudinal concave notch. 



As for the orbital cavity itself, its walls are but fairly entire, \\\^ pars 

 plana being small, and the exit from the brain-case for the first nerve 

 being far larger than this branch demands. Moreover, the palatines 

 being vertical plates in this situation, and the pterygoids slender, the 

 floor of the cavity is necessarily badly provided for in this regard. 



In both these specimens the foramina for the exit of the optic and 

 the third, fourth, and sixth nerves are distinct, and scarcely any greater 

 in size than the structures they are designed to transmit are in calibre. 



The interorbital septum is without vacuities, and merges directly 

 throughout with the rostrum of the sphenoid beneath it, the lower 

 margin of the whole plate being sharp, both interiorly and in front. 



Anteriorly the ethmoid bone proper is very broad, being spread out 

 as an abutment against, and bordering for all its width, the posterior 

 line of the cranio-facial hinge. The body of the bone is thickened 

 and filled in with diploic tissue. 



That portion of the skull which lies behind and below the orbital 

 ring presents for examination, above, the lateral aspect of the evenly- 



