SKULL^GANOIDS 



lOI 



hypophysial fossa is perforate in the aduU. The synotic tectum is considerable, 

 and in front of it is a transverse bar with the epiphysial foramen, the bar sepa- 

 rating anterior and posterior fontanelles. The thin-walled nasal capsules are 

 connected by an internasal roof. A large fenestra between sphenolateral and 

 trabecular cartilages gives exit to the optic nerve. There is a strong ridge on 

 the otic capsule for articulation with the hyomandibula, and the posterior ends 

 of the parachordals extend down around the aorta. The pterygoquadrate 

 articulates in front with the ethmoid region, and its hinder end is supported by 

 the hyomandibula which is dumb-bell-shaped, possibly indicating a symplectic 

 part, though none occurs in the adult. The four gill-arches are very slender, 



Fig. io8. — Chondrocranium of Polypterus (Budgett, '07). h, branchials; ch, 

 ceratohyoid; hh, hypohyal; hm, hyomandibular; lb, labial; mk, Weckelian; op, oper- 

 culum; pq, pterygoquadrate; sh, stylohyoid; 2-7, nerves. 



the anterior reaching the cranium behind the hyomandibula. These arches are 

 well ossified in the adult, some of them forming a suprapharyngeal bone as in 

 many Teleosts. 



The chondrocranium largely persists in the adult, but contains 

 several cartilage bones (hg. 109, A) including mesethmoid, a pair each 

 of ectethmoids, sphenotics and opisthotics. The hypophysial fossa 

 is partly enclosed by bone, possibly representing ali- and orbito- 

 sphenoids, while the posterior part of the floor contains the fused 

 basi- and exoccipitals, the latter meeting above the foramen magnum, 

 no supraoccipital being ossified. The adult cranium (fig. 109, B) is 

 covered by numerous membrane bones, some large, others small and 

 apparently formed by fusion of a few scales. The cranial roof is 

 formed by parietals, frontals and nasals, with a small *adnasal' in 

 front of each nasal, and the mesethmoid visible between them. A 



