i 4 ELOPIFORM FISHES 



stage, directly comparable to Tarpon but more advanced than that described for 

 Heterotis where according to Greenwood (1968) there is also a pleural rib and epi- 

 central bones associated with this centrum. It is generally assumed that the 

 neural arches associated with this centrum are lost in most teleosts but the situation 

 may be more complex since Gosline (1969) records that in Alepocephalus the neural 

 arches have become detached from the centrum and are incorporated into the neuro- 

 cranium. Clearly the occipital condyle region of the teleost neurocranium warrants 

 closer attention. 



The prootic is the largest endochondral component of the neurocranium and, as 

 is usual in teleosts, is complicated in shape. The prootic is disposed in a vertical 

 and horizontal plane, the former consisting of transverse and longitudinal faces. The 

 horizontal part of the prootic extends medially from the lateral face beneath the level 

 of the pars jugularis and meets its fellow in the mid-line, so forming the prootic 

 bridge. The anterior margin of the prootic bridge is deeply indented in the mid- 

 line, forming the posterior margin of the pituitary foramen. The anterior border 

 of this foramen is formed by the basisphenoid. Posteriorly the prootic bridge is 

 sutured with the basioccipital so separating the cranial cavity above from the pos- 

 terior myodome below. The abducens nerve pierces the prootic bridge near to its 

 junction with the lateral vertical face of the prootic. 



The lateral vertical face of the prootic is depressed postero-dorsally where it 

 forms the anterior region of the subtemporal fossa. Postero-ventrally the prootic 

 is inflated to form part of the wall of the otolith chamber. Within the lateral face 

 of the prootic runs the long pars jugularis. Posteriorly the pars jugularis opens to 

 the lateral face of the neurocranium by the jugular foramen, close to the prootic- 

 exoccipital suture. Immediately above the jugular foramen the prootic is raised 

 into a short spine which extends posteriorly and interdigitates with an anterior limb 

 of the intercalar. The hyomandibular foramen opens to the surface of the prootic 

 above the level of the pars jugularis to which it is connected by a short canal. Above 

 the foramen the path taken by the hyomandibular ramus is seen as a faint groove. 

 From the floor of the pars jugularis a short canal passes ventrally through the 

 prootic and splits into two branches, one opening on the medial face, the other on 

 the lateral face. The former carries the palatine branch of the facial, the latter 

 carries the orbital artery. 



The medial wall of the pars jugularis is perforated by a single large foramen 

 through which pass the roots of the trigeminal, facial and profundus ciliaris nerves. 

 The pars ganghonaris is simply represented by a small depression on the medial 

 aspect of the prootic. The gasserian and geniculate ganglia are lodged within this 

 depression. 



The anterior, transversely orientated face of the prootic is small. It meets the 

 autosphenotic and pterosphenoid dorsally, the basisphenoid ventro-medially and 

 the parasphenoid ventro-laterally. Medial to the large anterior opening of the pars 

 jugularis there is a smaller oculomotor foramen. 



The autosphenotic is tetrahedral, the apex of the tetrahedron being produced 

 laterally as a small spine to which the levator arcus palatini musculature is attached. 

 Laterally the autosphenotic forms the anterior part of both the dilatator fossa and the 



