ESPECIALLY MYCTOPHOIDS 209 
The prootic forms much of the lateral wall of the cranial cavity and myodome as 
well as a certain part of the posterior wall of the orbit. Ventrally the prootic is thin, 
meeting the parasphenoid below and the exoccipital behind. More dorsally the 
prootic divides into two layers, an outer layer inclining dorso-laterally and an inner 
layer passing medially to form the roof of the posterior myodome. The outer layer 
contacts the sphenotic in the hyomandibular facet and the pterotic below the mid- 
region of the same facet. 
The lateral region of the cranial cavity below the hyomandibular facet takes the 
form of a triangular depression. The posterior boundary of the lateral wall of the 
cranial cavity is formed from a stout strut of bone composed dorsally of pterotic and 
ventrally of exoccipital. The intercalar is superficial in position and plastered 
around this strut, covering the suture between the pterotic and exoccipital. The 
intercalar is, then, an elongated oval bone appearing on both the lateral and posterior 
faces of the neurocranium. 
The inner sheet of prootic contacts its partner in the mid-line to form the prootic 
bridge separating the myodome from the cranial cavity. The arms of the basi- 
sphenoid articulate with the anterior edge of the prootic bridge. The trigemino- 
facialis chamber is divided by a bony wall into a medial pars ganglionaris and a 
lateral pars jugularis. The pars jugularis is a short horizontal canal, narrow 
posteriorly, and lying lateral to the prootic bridge in the angle between the internal 
and external layers of the prootic. There are two foramina entering the pars 
jugularis from the pars ganglionaris, arranged one above the other. The ventral 
foramen is the facial foramen through which passed the hyomandibular branch of 
the facial nerve. The dorsal foramen is the trigeminal foramen and through this 
passed the trigeminal, profundus and superficial ophthalmic nerves. The pars 
jugularis has four external openings ; the posterior one is small, merely transmitting 
the jugular vein. Dorso-laterally there is an extremely large, elongate foramen 
reaching up almost to the hyomandibular facet. This foramen directed the hyo- 
mandibular nerve upwards and outwards to the hyomandibular. The anterior 
opening of the pars jugularis is large and triangular, in the hind wall of the orbit. 
Through it the jugular vein, the orbital artery, the trigeminal, profundus and super- 
ficial ophthalmic nerves passed. The orbital artery entered the pars jugularis 
through the fourth opening which is ventro-lateral in position and close to the 
posterior opening of the pars jugularis. 
The parasphenoid is long and straight, extending for practically the entire length 
of the neurocranium. The anterior end, lying on the dorsal surface of the vomer, is 
narrow. Below the lateral ethmoids the parasphenoid is considerably widened, due 
to the presence of large lateral flanges, inclined slightly ventrally. In the mid-dorsal 
line of the parasphenoid a thickened pad of bone between the ascending processes 
provides the attachment region for the basisphenoid pedicel. The ascending 
processes arise at the level of the basisphenoid pedicel but are not particularly deep 
and contact the prootics dorsally in the wall of the myodome. Near the base of the 
ascending process a slight depression marks the articulatory point of the first 
pharyngobranchial. Above the depression, the foramen of the internal carotid 
