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ME. W. K. PAEKEE ON THE STEUCTUEE AND 



But the section of the right side, just a degree further back, is most instructive. The 

 large superoccipital cartilage is seen embracing and walling in the great sinus (s.o., l.s.), 

 and the periotic mass is severed at the junction of the anterior and posterior canals, so 

 that the tube ftpened here is the " common canal " (c.c). The posterior non-ampullar 

 half of the horizontal canal (h.s.c.) is opened over the hinder part of the tegmen tympani. 

 The promontory is cut through at the fenestra rotunda (^?r., f-r.), and outside this is 

 seen the head of the stylohyal ; all this long sinuous rod (st.h.) is exposed, and also 

 the short ceratohyal {c.hy.) at its base, where it is seen articulating with the three 

 rudiments of the next arch (base and larger cornua of hyoid of Man). 



Reconstruction of the skull at this third stage from the foregoing materials will be 

 rendered easier by light obtained from longitudinally vertical sections (Plate XXXIII. 

 figs. 2 i& 3). In these the first is made, in the facial region, a little to the left of the mid 

 line, so as to give the left face of the septum of the nose ; in the next (fig. 3) the septum is 

 cut away, and the left face of the right turbinals exposed. In the first (fig. 2), the brain 

 is sketched in outline in situ ; in fig. 3 it has been removed to display the inner wall 

 of the cranium. The notochord [nc.) has retired from the posterior clinoid wall, and 

 has been buried in cartilage ; it still lies, however, nearest the upper surface of the in- 

 vesting mass. This may be compared with the like view in the first stage (Plate XXVIII. 

 fig. G). There the basifacial axis scarcely made a right angle with the basicranial ; 

 here these parts meet at an angle larger by one half: there the notochord mounted 

 above the investing mass ; here it has retired, and lies below the clinoid wall. 

 The gelatinous space called by Rathke the " middle trabecula " is gone, and the 

 reduplicated lining membrane of the cranium has formed the " tentorum cerebelli " 

 (fig. 2, t.ch.). The huge expansion of the hemispheres (C 1") has hidden the middle 

 vesicle (C 2), as seen from the outside. Behind the large cerebellum (C 3) the occi- 

 pital cartilage {s.o.) is seen in section ; and below the rounded margin of the basiocci- 

 pital [h.o.) is shown, the tract becoming thinner forwards, and then much thicker close 

 to the pituitary body {pij.)] it ends above in the overlapping "posterior clinoid wall" 

 (p.cl.). The pituitary depression is not saddle-like, but is a deep cup, floored by a good 

 plate of cartilage. The anterior clinoid wall [a.cl.) is rounded, and belongs to the 

 presphenoid; the depression in front of it is for the optic chiasma. The median 

 plate rises gently in front of the optic depression, and this higher part for a short 

 distance belongs to the anterior sphenoidal territory : it is formed principally by the 

 trabecular commissure and crests. The rest of the plate belongs to the perpendicular 

 ethmoid and septum nasi ; the latter is the longest region and the former the highest. 

 The lateral ethmoid [al.e.) is scarcely seen in this view (fig. 2). Below the pituitary 

 body the Eustachian opening {cu.) is seen, in the root of the tongue the ceratohyal 

 {Uj., c.hj.), and in the substance of the lower jaw the commissure of Meckel's carti- 

 lages {)n/c.). 



These things and some others are seen in the next figure (fig. 3). Outside the fora- 

 men magnum (f.m.) is seen the occipital condyle (o.c.) ; in front of this the " anterior 



