. Bonner zoologische Monographien. Zoology. 87 Exoccipital (, 50). In cyprinids, the exoccipital is a paired endochondral bone placed at the posterior portion of the neurocranium. The exoccipital forms the ventral portion of the braincase's posterior wall and a part of the foramen magnum. The exocci- pital sutures with the epioccipital and supraoccipital dorsally and basioccipital ventrally. On the ventral view, it sutures with the prootic anteriorly, basioccipital medially, epiocci- pital and pterotic anteriorly. The right and left exoccipitals suture one another mesially. A cavum s
. Bonner zoologische Monographien. Zoology. 87 Exoccipital (, 50). In cyprinids, the exoccipital is a paired endochondral bone placed at the posterior portion of the neurocranium. The exoccipital forms the ventral portion of the braincase's posterior wall and a part of the foramen magnum. The exocci- pital sutures with the epioccipital and supraoccipital dorsally and basioccipital ventrally. On the ventral view, it sutures with the prootic anteriorly, basioccipital medially, epiocci- pital and pterotic anteriorly. The right and left exoccipitals suture one another mesially. A cavum sinus impar is present between the dorsal margin of the basioccipital and the middle portion of the ventral margin of the exoccipital. Posteriorly, the exoccipital extends laterally and expands medially in Phoxinus. The me- sial edge of the exoccipital is laterally concave, therefore the foramen magnum is formed between the two exoccipitals laterally and supraoccipital dorsally. A lateral occipital fo- ramen is also formed on the exoccipital at the base near the medial margin. Viewed dor- sally (after the supraoccipital and epioccipital removed), the left and right exoccipitals form a butterfly-shaped structure^ Each of the two exoccipitals extends laterally to form the "wing" portion of the "butterfly" (, 50), and the middle part of the bone forms the "body" (, 50). At the median of the exoccipital is a thin and flat plate-like portion (Figs 49A-B, 50) which meets its counter part at the medial side of the exoccipital. The plate-like portion of the basioccipital bears two dorsal crests at the dor- sal aspect of the bone (see also the description of basioccipital below). These two dorsal crests of the basioccipital form a canal whereas the plate-like structure of the exoccipital roofs the canal-like structure (). Variation of the exoccipital among the Phoxinus species includes shape of the wing por- tion and the posterior m
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