208 MR. W. K. PARKER ON THE OSTEOLOGY 
with the posterior semicircular canals. Above the venous canals the bone is somewhat 
depressed, and it is here that the epiotic (mastoid) and opisthotic have combined ; on 
the outer edge of the more than semicircular occipital plane, we have the tympanic 
wings of the lateral occipitals—low, thick, slightly everted externally, evenly bevelled 
in front, and thoroughly struthious (Pl. XXXIV. fig. 8, co., and Pl. XL. figs. 1 & 3). 
In harmony with what is found in other parts of the skull, the occipital condyle (Pl. XL. 
fig. 1) is neither struthious nor gallinaceous ; for in Ostriches the condyle is generally 
broadest from side to side, and dimpled behind; in the Fowls it has become reniform. 
But in the Tinamou, although the dimple is retained in the knob itself, it is longest from 
fore to aft—an exaggeration of what we find in the Plovers, and, but for the dimple, pre- 
cisely like what exists in the most typical birds, the Crows. I have before remarked upon 
this forestalling of typical characters in birds just breaking out from the Ostrich fence. 
The basitemporal region (Pl. XL. fig. 1) reveals the Ostrich at once; for the tym- 
panic lateral ale are aborted, and this, taken in connexion with the blunted margins of 
the lateral occipitals, shows a low and generalized condition of the tympanic cavity, which, 
save in its Eustachian elongation forwards, is very shallow, and is principally formed by 
the scooping-out of the outer face of the periotic capsule, neither the tegmen nor the 
inferior lip of which were ever much developed (Pl. XL. fig.3). As far as I have at pre- 
sent seen, there is no ossification of the fibro-cartilaginous rim of the membrana tym- 
pani in the Ostriches and the Tinamou; yet this ossification is singularly constant, 
although very diverse in condition, in all the more typical families of birds. This again 
is obviously general and reptilian. ‘The basitemporals are not nearly so defined in the 
adult Tinamou as in the Rhea (PI. XLII. fig. 1, b¢.); their anterior margins meet in front 
at the mid line, and form rather more than a right angle; yet this margin only forms a 
smooth ridge, in front of which the bone (basisphenoid) is somewhat scooped ; whereas 
‘in the Rhea there is a free lip behind and external to the Eustachian openings (ew.). 
These openings are relatively much further apart in the Tinamou (PI. XL. fig. 1) than in 
the Rhea; and in the latter the external half of the Eustachian tube is floored beneath 
by the coalescence of the basitemporal with its corresponding posterior pterygoid 
process (Pl. XLII. fig. 1, bt. & p.pt.): in the Tinamou, only a third of this duct is thus 
protected. In this respect the Rhea comes nearer the Fowl than the Tinamou. In the 
Fowl-tribe the internal carotid artery (PI. XXXVI. fig. 6) is protected twice as far back- 
wards as in the Tinamou; and the whole width of the combined basitemporals is only 
half as great in the latter as in the former. Yet, as far as thickness is concerned, there 
is but little difference between the Fowl and the Tinamou ; and this thickness is in both 
cases dependent upon the fact that the bony copy is like the cartilaginous pattern ; for 
the ‘‘ investing mass ”’ is very solid in this region in both groups, the great difference 
being that in the Fowls a more complete floor is formed to the periotic capsules by the 
lateral extension of the cartilage surrounding the pointed end of the notochord. The 
foramina for the vagus, ninth nerve, and condyloid vein are of moderate size, and are well 
