78 UPPER CRETACEOUS TELEOSTS 
with very slight expansions on either side, in the form of ventro-lateral flanges. The 
ventral surface has a shallow longitudinal groove, whereas the dorsal surface has 
a very low longitudinal ridge. Each ascending process of the parasphenoid meets 
the prootic laterally, and its anterior edge, bordering the myodome, is thickened. 
Posteriorly the ascending process is considerably thinner where it forms the wall 
of the myodome. In the antero-ventral region of the ascending process is a fora- 
men through which the internal carotid artery passed. The posterior part of the 
parasphenoid articulates with the ventro-lateral edges of the basioccipital, and ends 
posteriorly immediately below the occipital condyle. The postero-ventral region of 
the parasphenoid takes the form of a median keel. This keel occludes a certain 
amount of the lumen of the posterior myodome and the myodome does not open 
posteriorly. 
The prootic merits particular attention due to its complexity. The ventral part 
of the bone consists of two vertical laminae joined anteriorly. The inner sheet 
contacts the basioccipital behind and separates the myodome from the otolith 
chamber. The outer sheet forms the wall of the anterior part of the otolith chamber 
and meets the parasphenoid below and the basioccipital and exoccipital behind. 
The inner sheet curves medially and fuses with its partner from the opposite side 
forming the prootic bridge which separates the myodome from the cranial cavity. 
Posterior to the prootic bridge the otolith chambers communicate with the cranial 
cavity through a large oval fenestra. Above the prootic bridge the orbital face of 
the bone is roughly triangular, the apex of the triangle being directed ventrally. 
This region contacts the sphenotic dorso-laterally and the pleurosphenoid dorso- 
medially. Medially the edge of the prootic above the prootic bridge forms the 
margin of the lower part of the optic fenestra. The dorsal region of the lateral 
surface of the prootic is inclined dorso-laterally at about 110° to the ventral region. 
This upper region meets the exoccipital posteriorly, and the pterotic and sphenotic 
dorsally just below the hyomandibular facet. The prootic does not enter into the 
composition of the hyomandibular facet, which is produced solely from sphenotic and 
pterotic. 
The prootic contains the trigemino-facialis chamber (Text-fig. 38A), which is 
divided by bone into a medial pars ganglionaris and a lateral pars jugularis. The 
former is a recess on the medial face of the bone, within the cranial cavity, lateral to 
the anterior part of the prootic bridge, and which housed the ganglia of the trigeminal 
and facial nerves. The pars jugularis is an extremely short horizontal canal on 
the lateral face of the prootic lateral to the prootic bridge, and in the angle between 
the dorsal and ventral parts of the lateral surface of the bone. There is a single 
foramen leading from the pars ganglionaris into the pars jugularis, this being the 
facial foramen which transmitted the hyomandibular trunk of the facial nerve. 
The palatine branch of the facial nerve did not enter the pars jugularis but passed 
through a small foramen medial to the facial foramen into the myodome. The pars 
jugularis has two external openings, one posterior and one anterior. Through this 
very short canal passed the jugular vein and the orbital artery. The posterior 
opening also transmitted the hyomandibular branch of the facial nerve. The 
