104 NEW YORK STATE MUSEUM 



mental stages of the skull which are past finding out in the skull of 

 the adult individual of this species. 



For instance, the mesial margin of the supraorbital process of the 

 lacrymal .seems to articulate only with the nasal at this age. The 

 frontal processes of the nasals curve mesiad toward each other so 

 as to meet in the middle line over the mesethmoid and premaxillary. 

 The circular nostril is not completely formed, the nasal not having 

 filled, in its share from above and behind. And, as we would 

 naturally expect, the anterior wall of the brain case and the inter- 

 orbital septum are now very deficient in bone. Even at this tender 

 age, however, the Eustachian tubes are closed in by bone along 

 their lengths in front. 



Skulls of a number of other falcons have been carefully com- 

 pared and examined by me, but there seems to be nothing to record 

 worthy of special notice in the present work. Falco mexi- 

 canus offers us in its skull all the main features of that part of 

 the skeleton in the genus Falco, and these have been quite fully set 

 forth above, and in sufficient detail for our requirements. 



Representatives of the genus Falco have some very excellent 

 distinguishing characters in the skeleton of the remainder of the 

 trunk and in the pelvic limb. 



Turning again to our series of skeletons of Falco mexi- 

 c a n u s , and this species presents practically all the osteological 

 characters for these true falcons, we find that in the first place it 

 has 20 vertebrae between the skull and pelvis ; 12 in the pelvic 

 sacrum; and 7 plus a pygostyle in the skeleton of the tail. There 

 are three pairs of cervical ribs, the first being very rudimentary. 

 Four of the leading dorsal vertebrae and the last cervical fuse to- 

 gether to make one solid bone. The last dorsal is free. Six 

 haemapophyses articulate with the costal border upon either side of 

 the sternum; the ultimate pair of these are from the sacral pair of 

 vertebral ribs. 1 



The pygostyle is large, often pierced by a foramen, and its 

 superior border is long and very slightly curved. Beneath the pos- 

 terior part of the pygostyle the tendons of insertion of the lateralis 

 coccygis, on either side, ossify (not only in F . mexicanus but 

 in all true falcons). The vertebral ribs are very slender compara- 

 tively, as are their long epiplciiral appendages that fuse with them. 

 They are absent on the sacral or pelvic ribs. 



1 In specimens of Falco sparverius before me, this last pair of costal ribs 

 does not meet the sternum; and this may occur in Falco mexicanus. 



