286 MR. W. p. PYCilAFT ON THE [^Pl'- l^J 



with an ossification of the basis of the choncha media which 

 projects into the cavity from the outer wall. In the true Falcons 

 the ossification of the aliethmoid causes the anterior nares to be 

 I'ouncl in form as in life, in Polyhoroides crescentic. In both, the 

 aperture displays within its mouth a small median bony papilla — 

 the papilla of the conchce vestibuhim of Suschkin, the alinasal 

 turbinal of W. K. Parker. The details of the strvicture of the 

 cai'tilaginous nasal labyrinth and its ossifications have been 

 exhaustively worked out and beautifully illustrated by Dr. Suschkin 

 in his masterly monograph on the skull of Tinnunculus. 



The Cranial Cavity. — Tl\\Qmetencephalicfossaoi theFalconifoi-mes 

 is more basin- shaped in the smallei- than in the largei- forms. 

 Moi-eover, in these smaller forms the anterior I'egion of the fossa 

 is tilted upwai'ds and backwai-ds so as to form an acute angle with 

 the long axis of the skull. The trigeminal foramen, in Falco for 

 instance, is sharply cut off from the mesencephalic fossa by an 

 ovei'hanging ledge of bone. The orbito-nasal foramen also lies 

 immediately under this ledge. In the Vultures, the upper ledge 

 of bone overshadowing these apei-tvires is less extensive, so that 

 they come to lie partly in the flooi- of the mesencephalic fossa. 

 The apei'tures of the vagus and internal auditoiy meatus do not 

 offei' any very important points of difference for comment. 



The cerebellar fossa is sharply defined and vaiiable in I'elative 

 proportions, being, for instance, lai-gei- in Falco than in Vultur or 

 Circus. The foccidar fossa is, in Falco, cordiform, and apparently 

 rather shallowei- than in other forms. 



The mesencejyhalic fossa is very sharply defined. It is banded 

 above by a broad overhanging ledge formed by the tentorial lidge. 

 The distinctness of its inferioi' border is bluiTed, in Vtcltior, by 

 the apertures of the trigeminal and orbito-nasal nerves, which lie 

 in the floor of the fossa. In Falco these are shut ofi' from this 

 fossa by a bony shelf, and open inward into the dorso-lateral 

 border of the metencephalic fossa. 



The jnticitary fossa is deep and tubulai-, and passes almost 

 vertically downwards. The hinder boundary of this fossa, the 

 dorsum sellce, forms a nai'i-ow lidge passing forwards and upwards 

 to tenuinate above the oculo-motoi' foi-amen. The anterior 

 border of the fossa is boiuided by the ti-ansverse pre-pituitaiy ridge, 

 which passes forwards into a narrow, sometimes triangular, ojDtic 

 platform, on either side of which lie the optic foramina. The 

 optic platfoiin is continued upwards, forwards, and backwards 

 into the j^re-Ojytic ridge which may be traced, in Circus for instance, 

 on either side into the tentorial ridge. In the majority of othei- 

 forms, probably, it disappears before i"eaching this, e. g. Vtdtur, 

 Falco. 



The ocido-motor lies immediately caudad and ventrad of the 

 optic foramen. It is continued backwards in a rather wide groove 

 into the dorsum selkie. Below and antei-ior to this foramen is 

 the aperture for the internal ophthalmic artery — when this is 

 separate. It opens into the pituitary fossa some distance from the 



