400 PEOF. T. JEFFEET PAEKEE ON THE CEANIAL OSTEOLOGY, 



Afteryx is the only genus besides the Dinornithidse which has a well-marked 

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

 edged supratym panic 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 Dinornithidse, 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 Dromceus (fig. 67) and Casuarius 

 (fig. 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 Bhea (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 Apteryx 

 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 

 antcro-lateral by the alisphenoid. 



The anterior tympanic recess is large in aU genera but Apteryx. The Ostrich diff'ers 

 from the others in having a large {gu. venous'?) 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 Eatitse 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 Rhea the 

 squamosal sends off", 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 head of the quadrate. 



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

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

 temporal ridge. In Apteryx, on the other hand, the temporal fossa is very wide from 



^ In my paper on Apteiyx (24) I incorrectly 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 off a posterior part furnished by the truncated end of a bar-like process of the exoccipital just above 

 the fenestra 1 recess. 



