4 8 



ELOPIFORM FISHES 



20mm soc 



exo 



pap 

 Fig. 21. Tarpon atlanticus (Cuvier & Valenciennes). Neurocranium in posterior view. 



and lateral border of the post-temporal fossa. The exoccipital is large, forming the 

 ventral border to the post-temporal fossa opening, and the dorsal and lateral margins 

 of the foramen magnum. Along the medial border of the post-temporal fossa the 

 exoccipital forms a ridge which is continued on the epiotic. Medial to this ridge 

 both bones exhibit concave posterior faces. Thus the surface topography of these 

 bones results in there being a median depression flanked on either side by the post- 

 temporal fossae. Beneath the foramen magnum the exoccipital bears a facet which 

 articulates with the first vertebral centrum. On the lateral face of the exoccipital 

 and basioccipital there is a prominent postero-ventrally inclined ridge which provides 

 a point of attachment for the anterior diverticulum of the swimbladder (Greenwood 

 1970a has described and figured the extension of the swimbladder on the otic region 

 of the skull). Baudelot's ligament inserts on the posterior face of the basioccipital 

 part of the ridge. The exoccipital also contributes to the subtemporal fossa. 

 Beneath the subtemporal fossa the exoccipital exhibits a marked depression. Into 

 the upper part of this depression (which is covered in lateral view by the intercalar, 

 not described here, see Greenwood 1970a) opens the vagus foramen, immediately 

 preceded by the much smaller glossopharygeal foramen. The jugular vein runs 

 along the roof of this depression. 



Beneath the exoccipital the basioccipital forms the inner wall of the periotic bulla. 

 The ontogenetic changes that affect the basioccipital are discussed by Greenwood 

 (1970a). 



