278 PROF. W. K. PARKER ON THE STRUCTURE AND 



The single occipital condyle (oc.c) is an elegant crescent, embracing the notochord (nc) ; 

 much of that rod is naked behind on the lower surface, but is invested in front, and is 

 only seen again at its apex in the back of the round pituitary space (pi/). The whole 

 of the hinder chondrocranial walls are very distinct from the larger lobulated auditory 

 capsules (au). Here the hypoglossal nerve (xii) passes through the " posterior condy- 

 loid foramen" (Miall)^ 



The cochlear diverticula of the auditory capsules (cJil) have coalesced with the basal 

 plate (iv); but laterally, and above, the occipital arch is quite distinct from them, and 

 where the ninth and tenth nerves (ix, x) emerge there is a large oval open space. 

 Above, the supraoccipital cartilage roofs in three fourths of the hind skull, forms a 

 flange on each side to the back of the auditory capsules, has concave lateral edges and 

 then spreads out again, but to a lesser degree, in front of the capsules. The ascending 

 fore end of the double basal plate is now a continuous slanting wall of cartilage 

 leaning over the pituitary space behind (fig. 1, j).cl, pi/). From this wall a flying 

 buttress is thrown across, right and left, and this buttress passes into the thickened 

 coping of the alisphenoidal wall (al.s). That thickening is developed behind into a 

 crescentic horn, which embraces the front outer corner of the auditory capsule ; this 

 process is very thick and strong below (flg. 2), and the two hold, like opened tongs, the 

 swollen front lobes which have the anterior ampullae (a.s.c) inside. The thick top of the 

 alisphenoidal wall {al.s} runs beyond that limited part, and curving round, passes into 

 the hind corner of the orbitospheuoid (o.s) ; thus there is below a large " orbito-alisphe- 

 noidal fenestra" {o.al.f). Below each flying buttress, sent out from the postclinoid 

 wall, there is a large recess ; it has the auditory capsule above and outside it, and the 

 basal plate [iv) bounding it below and towards the middle ; this is the huge primary 

 " foramen ovale " (v) for the trigeminal nerve and Gasserian ganglion. In front and 

 below, the alisphenoid {al.s) grows downwards, margining the pituitary cup above, and by 

 a thick inturned process uniting with that cup as a partial rim. There is, then, infero- 

 laterally, a lesser crescentic fenestra, the " lower or alisphenoidal fenestra " {al.f) ; this 

 transmits the lesser preauditory cranial nerves. The rest of the alisphenoid is a narrow 

 convex band, which runs forwards and inwards, and is confluent with the postero- 

 inferior angle of the orbitospheuoid {o.s) ; where these two bands converge to join the 

 orbitosphenoids, there, on the upper surface, we see the foramina for the optic nerves 

 (fig. 1, ii) ; these are separated by the sharp top of the intertrabecular bar {i.tr). 



The long rod-like structure which forms the base of the prepituitary region of the 

 skull encloses the front and sides of the circular pituitary space, below, by its forks ; 

 these short forks are mamillated at their end, and project from the general surface 

 of the cartilage. They converge rapidly to embrace the intertrabecular bar, which is 



' In my former papers on the skulls of the Sauropsida, led by the analogy of the Mammalia, I have con- 

 sidered the anterior condyloid foramen as the passage for the hypoglossal nerve. 1 suppose that dissection 

 would show that I have been in error. 



