188 REPORT—1846. 
question to he determined, therefore, is, what are the essential characters re- 
spectively of the ‘alisphenoid’ and the ‘ petrosal’ in the vertebrate series ? 
Those of the alisphenoid appear to me to be the following :—1st, its con- 
nection below with the basisphenoid and behind with the petrosal, where it 
forms the forepart of the ‘ otocrane’ or cavity for the reception of that osseous 
or cartilaginous immediate capsule of the labyrinth or internal organ of hear- 
ing: the alisphenoid is also commonly, but not constantly, joined before 
with the orbitosphenoid, and above with the parietal: it has other less con- 
stant connections with the squamosal, the exoccipital, the supraoccipital and 
the basioccipital: 2ndly, with regard to its essential functions, the alisphenoid 
protects more or less of the side of the mesencephalon, or (in mammals) of 
the middle lobe of the hemisphere: it gives exit, by notches or foramina, to 
the third, and usually, also, to the second divisions of the trigeminal or fifth 
pair of nerves. 
The essential character of the petrosal is to envelope immediately the 
whole of the vascular and nervous tunics of the labyrinth or internal organs 
of hearing, either in a membranous, a cartilaginous or an osseous state ; 
its histological condition being much less constant than that of the alisphe- 
noid. 
On viewing the alisphenoid on the interior surface of the human skull 
(fig. 6, 6), it seems to be the least significant and important part of the lateral 
Fig. 6. 
Vertical longitudinal section of the human cranium, 
walls of the cranial cavity: it forms their smallest portion: it is much sur- 
passed in extent by the squamosal (2b. 27) and the supra-occipital (2b. 3), 
and still more so by the enormously expanded parietal (7) and frontal (11). 
Nevertheless we find it connected, anchylosed indeed, below to the basisphe- 
noid (5), bounding anteriorly the space into which the petrosal (16) is 
wedged; connected in front with the orbito-sphenoid (10), and usually 
articulating by its superior apex with the parietal: I purposely omit the 
mention of other connections of the alisphenoid in Man which are less 
constant in the vertebrate series. But it is important to observe, notwith- 
standing the displacement which the alisphenoid has undergone through the 
intercalation of the extraordinarily developed squamosal into the lateral walls 
<——t 
