DEVELOPMENT OP THE SKULL IN THE OSTEICH TEIBE. 143 



is completely ossified, and the sinus canal is well walled in ; the whole region is very 

 similar to what is seen in the Apteryx. 



Inside the skull the opisthotic is seen as a distinct wedge of bone, with its sharp end 

 downwards, but the supcroccipital has taken up most of the epiotic region — not all, for 

 this bone, although small, is now to be well seen, roofing in the little lateral lobe of 

 the cerebellum behind. The external lamma of the epiotic (Plate XI. fig. 10, ep.) is 

 only to be seen by paring away the large outer angle of the supcroccipital ; the bone 

 is subquadrate, gently concave within, whilst on the outside it is as gently convex. The 

 external surface of the bone is absorbed towards the mid line of the skull to form a large 

 pneumatic foramen, which connects the holloAV interior of the bone with the diploe of 

 the supcroccipital. Inside the skull, both below and above the small epiotic, a small 

 synchondrosis exists between the prootic (Plate XI. fig. 10, pro.) and the supcrocci- 

 pital ; the upper is the largest, and is at the anterior third of the great anterior semi- 

 circular canal {a.s.c.); the rest of the large prootic is well ossified, both within and 

 without. The nature of the bar of bone formed by the opisthotic (Plate XL fig. 10, 

 & Plate XII. fig. 5, op.), which separates the auditory fenestrse (f. ovalis and f. rotunda), 

 can be weU seen at this stage; above the head of the " stapes" (Plate XI. fig. 10, st.), 

 which lies in the fenestra ovalis, the suture separating the epiotic from the»opisthotic 

 (Plate XII. fig. 5, ep. op.), externally, is well shown. Returning to the base of the 

 skull, we find the combined basitemporals and basisphenoid (Plate XII. fig. 2, b.t., h.s.) 

 forming a very elegant structure ; the former are oval masses 2 lines across, the latter 

 is seen as a large four-winged mass, sending forwards a long, gradually attenuating 

 style (r.b.s.). One very small passage still exists in the front of the pituitary space, 

 which has become convex by a triangular mass of bone with the apex fon^'ards ; 

 laterally the Eustachian grooves (Plate XII. fig. 2, Eu.) have become much better 

 defined ; behind them we see the internal carotids (i.e.) grooving the basitemporals. 

 The "posterior pterygoid processes" (p.r.p.) are extremely large, and cellular ante- 

 riorly, the scooping of each plate passing into one common vacuity in the very body of 

 the basisphenoid ; all this is truly ornithic. The bone is very wide between the " ante- 

 rior pterygoid processes," which project outwards, downwards, and a little forwards. 

 Where the basisphenoid meets the basioccipital below, it is somewhat split (Plate XII. 

 fig. 2), and here the suture between the lateral and median basisphenoidal elements can 

 be still seen; the basitemporals are dentate, as they underlap the occipito-sphenoidal 

 synchondrosis; a little cartilage separates them from the basioccipital behind these 

 teeth. The delicate pointed end of the rostrum (r.b.s.) reaches to the same vertical 

 line as the front of the upper ethmoidal plate; it lies in the well-marked vomerine 

 groove. 



The prepituitary portion of the basisphenoid (Plate XII. fig. 1, b.s.) is still 4 lines 

 from the ethmoid; the well-ossified alisphenoids have, at their supero-external angle, 

 a small epiphysis, the " postfrontal " (Plate XII. fig. 1, a.s.,p.f.). The bony centre at 

 the junction of the orbito-sphenoids with the descending presphenoidal plate is now 



