15 
side being the larger and more densely calcified. They are 
bounded by the frontal, alisphenoid, prootic, pterotic and 
parietal. 
Prootic or Petrosal (Pr.0., figs. 2, 3)—A stout bone 
containing a quantity of cartilage. It is perforated by the 
large canal or foramen jugulare (f.jug.), which transmits 
the internal jugular vein, the ophthalmic artery and the 
truncus hyomandibularis nervi facialis. It also forms 
the postero-lateral wall of the trigemino-facial foramen 
(f.tr.fa) and the external wall of the carotid foramen 
(f.car.), transmitting the internal carotid artery. Further 
it forms the internal and lower half of the hyomandibular 
cup (Hm.F’.'), and its part in forming a false floor to the 
cranial cavity by processes of bone and cartilage has been 
already mentioned. The prootic has two conical depres- 
sions on its cerebral surface, the ventral one being much 
the larger. It is bounded by the parasphenoid, 
alisphenoid, sphenotic, pterotic and basioccipital. 
Epiotic (Hp.0., figs. 1, 5, 4)—A dense structure 
largely cartilaginous, but having a thin outer shell of 
bone, prolonged into the somewhat prominent epiotic 
process (H'p.P., fig. 4). The cerebral surface bears two or 
three deep conical pits with a thin bony lining, cne being 
much larger than the others. The epiotie provides the 
remainder of the cartilage for the occipital cross already 
mentioned. It is bounded by the supraoccipital, parietal, 
pterotic and exoccipital. 
Pterotic (Pt.0., figs. 1, 2, 5)-—Forms the greater part 
of the parotic process (Pa.P., fig. 4). It is more densely 
caleified than the epiotic, and its cerebral surface bears 
three deep conical pits, one being partially subdivided 
into two. Laterally it bears an imperfect oval bony facet 
for the posterior condyle of the hyomandibular (/m./.?, 
figs. 2, 3, and ep. fig. 5). The left facet is appreciably 
