90 



Basicranial Region 



The basicranial region forms the base of the braincase. Three single bones - vomer, pa- 

 rasphenoid, and basioccipital - are included in this region. 



Vomer (Fig.52A-D). In cyprinids, the vomer is a single bone, located at the most an- 

 teroventral portion of the neurocranium. Dorsally, the vomer connects with the meseth- 

 moid via the planum ethmoidale, as discussed above. Anteriorly, it attaches the kinethmoid 

 via ligaments. The anterolateral edge sutures with the preethmoid. 



In Phoxinus, the vomer is a plate-like bone bearing a notch at its anterior margin, a con- 

 striction at its lateral margin to form a waist, and a process at its posterior margin exten- 

 ding posteriorly and overlapping the ventral side of the parasphenoid. 



The process of the posterior margin of the vomer is elongated and sharp in P. phoxinus 

 (TS 83 [1]); this process is short and blunt in other species of Phoxinus and in the out- 

 groups (TS 83[0]). A T-shaped ridge is present at the anterior part of the vomer's dorsal 

 side in P. erythrogaster (TS 83 [1]); the ridge is not observed in other species of Phoxi- 

 nus and in the outgroups (TS 84[0]). 



Parasphenoid (Fig.53A-G). The parasphenoid in cyprinids is a dermal bone and can 

 only be observed in a ventral view of the neurocranium. It is underlaid anteriorly by the 

 vomer. 



In cyprinids, the parasphenoid sutures with the lateral ethmoid, orbitosphenoid, ptero- 

 sphenoid, and prootic dorsally from anterior to posterior. The orbitosphenoid connects with 

 parasphenoid via the orbital septum, as discussed above (however, in some minnows, e.g., 

 Crossocheilus, Labeo, Barbus, the parasphenoid bears a dorsal ridge, via which the para- 

 sphenoid contacts with the orbital septum - Ramaswami 1955a, Chen et al. 1984); the 

 pterosphenoid has only a small portion suturing with the ascending wing of the para- 

 sphenoid (see below). The posterior part of the parasphenoid overlaps the ventral side of 

 the basioccipital ventrally. The anterior portion of the parasphenoid (anterior to the as- 

 cending wing) is generally narrower than the posterior portion (posterior to the ascending 

 wing) in cyprinids. 



In Phoxinus, the parasphenoid is an elongated plate-like bone; a laterodorsally exten- 

 ding ascending wing is present at the middle of the parasphenoid; the anterior portion of 

 the bone is much narrower than the posterior portion. The anterior portion decreases in 

 size posteriorly. Dorsally, a ridge at the middle of the anterior portion is present which 

 contacts with the orbital septum. The ridge is well-developed in P. phoxinus and eos (TS 

 85[1]), and less developed in other Phoxinus species (TS 85 [0]). 



The ascending wing is more or less triangular and bent dorsally. A notch is present on the 

 posterior edge of each ascending wing and, with the prootic, forms the carotid foramen. 

 The notch is well-developed in P. neogaeus, oreas, issykkulensis, brachyurus, and phoxi- 

 nus (TS 86[0]); it is less developed in other species of Phoxinus (TS 86[1]). 



The posterior end of the parasphenoid is forked (Fig.53A-G). The fork is deep and ex- 

 tends to the middle of the posterior part of the parasphenoid in P. phoxinus (TS 87[1]); 

 the fork is much shallower in P. brachyurus, erythrogaster, eos, oreas, neogaeus, tennes- 



