400 PKOF. T. JEFFEEY PAEKER ON THE CRANIAL OSTEOLOGY, 



Avteryx is the only genus besides the Dinornithidse which has a well-raarked 

 tympanic ledge ; in all the others the cavity is bounded laterally only by the sharp- 

 edged supratympanic ridge. 



The quadrate facet on the roof of the tympanic cavity presents some interesting 

 variations in the various genera (Plate LXII. figs. 65-70). In the Dinornithidae, as we 

 have seen, it is almost regularly oval, its inner third furnished by the pro-otic and 

 exoccipital, its outer two-thirds by the squamosal (fig. 70). In StrutMo (fig. 65), at 

 about the middle of its anterior or mesial border, it is somewhat deeply notched ; as 

 all the specimens at my disposal were adults, the boundaries of the constituent bones 

 could not be made out. A similar notch occurs in BroiiKPUs (fig. 67) and Casuariua 

 Cfig. 68), and the facet is divisible into an inner or prootic-exoccipital and an outer or 

 squamosal region ; moreover, in the Cassowary the anterior edge of the external 

 region of the facet is encroached upon by the alisphenoid, which thus takes its share in 

 furnishing the articular surface. In Mhea (fig. 66) there is no notch, and the pro-otic 

 portion of the facet appears in an adolescent skull as a wedge of bone near the posterior 

 end of its anterior or mesial margin, and divided into a larger anterior and a smaller 

 posterior portion ; the posterior end of the facet is therefore formed mainly by the 

 exoccipital : the alisphenoid enters into the facet as in Casuarius. Lastly, in Apterijx 

 the facet (fig. 69) is distinctly divided into three portions — a mesial furnished partly by 

 the pro-otic, partly by the exoccipital ^, a postero-lateral by the squamosal, and an 

 antero-lateral by the alisphenoid. 



The anterior tympanic recess is large in all genera but Apteryx. The Ostrich differs 

 from the others in having a large {qu. venous 1) foramen excavated in the postero-ventral 

 region of the pretemporal wing immediately cephalad of the Eustachian groove. 



The zygomatic process is more slender in the other Ratitse than in the Moas, and is 

 directed outwards as well as forwards and downwards. The squamosal prominence 

 is always obscure, and there is never more than the merest trace of the posterior 

 tympanic fossa and ridge. In the Emu there is a distinct facet on the inner surface of 

 the distal end of the zygomatic process for articulation with the quadrate. In Ehea the 

 squamosal sends ofi", posterior to the zygoma, a process which passes forwards and is 

 nearly met by a similar process from the pretemporal wing, the two together forming 

 an almost complete ring round the posterior projection of the liead of the quadrate. 



The temporal fossa and ridge are far less strongly marked in the Ostrich, Khea, Emu, 

 and Cassowary than in the Moas, and in none of them is there any trace of the mid- 

 temporal ridge. In AiJtert/x, on the other hand, the temporal fossa is very wide from 



' In my paper on Apteiij.v (24) I incorrectlj- described this facet as being furnished exclusively by the 

 pro-otic, but a renewed examination of stage M shows a distinct suture passing vertically across it and 

 dividing oiF a posterior part furnished by the truncated end of a bar-like process of the exoccipital just above 

 the fenestral recess. 



