290 PKOF. W. K. PAEKEE ON THE STEUCTUEE AND 



The basisphenoid is equal to the basioccipital in size ; it is entirely surrounded by 

 cartilage, which intervenes between it and the basioccipital behind, the prootic (pr.o) 

 above and behind, and the alisphenoid (al.s) above and in front. There is no bone in 

 front of it, below, for the rest of the basicranial axis remains cartilaginous. 



The fore part of the basisphenoid (b.s) is hollowed out for the pituitary body and 

 internal carotid arteries, the hind part is pneumatic, the cavity running into the basi- 

 occipital. The bony matter is fast affecting the posterior clinoid wall ; and outside that 

 wall, a tract of cartilage intervening, there is an irregularly oblong bony tract on the 

 lower half of the alisphenoidal wall {al.s) ; this centre is pointed above, and square 

 below, it just reaches the large foramen ovale (v) behind. For the rest, the basicranial 

 axis and nasal septum [p.s,p.e,s.n,p.n) form a relatively larger tract than in the 

 last stage. 



The prootic bone (pr.o) is a thin ectosteal shell in the front wall of the auditory 

 capsule ; it runs upwards and backwards, with deep toothings, towards the meatus 

 internus (vii, viii) and the anterior ampulla [a.s.c). There is then on the arched fore 

 edge of the capsule an almost equal length of cartilage ; above that, the arch of the 

 anterior, and the beginning of the posterior, canal are covered with the second bony 

 tract, the epiotic (ej)) ; the upper edge of this bone forms a suture with the super- 

 occipital. 



Against the middle of the concave face of the exoccipital, on the inside, we see a 

 third lozenge-shaped bony tract ; this is the opisthotic (oj)) ; it runs round behind, 

 close outside the ampulla of the posterior canal, and is above and behind the great 

 chink for the glosso-pharyngeal and vagus nerves (ix, x). These periotic centres 

 appear to be rather more inside than outside ; they begin near the edge of the some- 

 what flattened capsule, and occupy about one fourth of its large sinuous superficies. 



All but the projecting angles of the great quadrate (PL LXIX. fig. 5, q) is ossified, 

 and this bony centre is becoming pneumatic. Also the postero-external face is much 

 more scooped, and the notch behind is semicircular. 



The soft fore angle of the otic process (ot.p) turns upwards, the hinder coi-ner down- 

 wards. A considerable core of cartilage remains over the lower condyle {q-c), and the 

 forks of the " orbital process " are unossified ;" the upper spur is the " ascending 

 process" {a.]}), and the front spur is the rudimentary "pterygoid cartilage" [p'j.c). 



Both the lateral cranial fenestrse are pyriform ; the lower is now two thirds the size 

 of the upper. The orbito-sphenoidal plate is relatively less ; a very small spike-shaped 

 rudiment of the anterior " tegmen cranii " exists, growing backwards from the top of 

 the perpendicular ethmoid [p.e). 



There is a small foramen below the upper fenestra ; and a space for the lesser cranial 

 nerves below and behind the optic passage (ii), which is circular, and nearly as large as 

 the foramen ovale (v). 



In this stage the various canals or passages can be well seen (PI. LXX. fig. 8) ; in 



