11] THE SKULL OF AMIURUS— KINDRED H 



the anterior margin of the otic capsule and below with the posterior end of the 

 trabeculae cranii thus enclosing the optic, oculomotor, trigeminus and facialis 

 nerves. It grows anteriorly to the ectethmoid process, an independent carti- 

 lage, and fuses with it. Dorso-medially it grows toward the middle line and 

 unites with its fellow of the opposite side to form the soUd cranial roof. Except 

 for its ventro-posterior relations, the ahsphenoid of Acanthias can be compared 

 to that of Amiurus. In both, these cartilages form the anterior and dorsal 

 margins of the foramina for the nerves mentioned above, and extend across 

 the dorsal part of the orbit. There is no cartilaginous roof in the chondro- 

 cranium of Amiurus with the exception of the epiphysial bar, which may be a 

 remnant of such a condition. The notch at the anterior margin of the optic 

 fenestra of Acanthias is suggestive of the orbital foramen of Amiurus, 



Parker (1882) recognized three cartilaginous parts in the lateral wall of the 

 orbital region of the chondrocranium of Acipenser ruthenus: a posterior alis- 

 phenoidal part, lateral to the parachordal plate; an anterior or bitosphenoidal 

 part; and a dorsal supraorbital part, which fuses with its fellow of the opposite 

 side to form the cranial roof. The orbitosphenoidal part is pierced by the 

 optic nerve and the alisphenoidal part by the trigeminus and the facialis. 

 This is more Uke the adult Acanthias cranium than it is Uke the cranium of the 

 developing Amiurus. 



In the chondrocranium of Lepidosteus osseus (Parker, 1882), the ahs- 

 phenoid cartilage curves anteriorly above the nerves, from the anterior edge 

 of the otic capsules. It is a thin flat bar and forms the lateral margin of the 

 almost circular fontanelle in the cranial roof. Ventro-anteriorly it unites with 

 the anterior ends of the trabeculae at the anterior end of the orbit, as in Amiur- 

 us. Medially and anteriorly it fuses with its fellow, above the fore-brain, 

 forming a sohd cartilaginous tegmen cranii, the remnant of which as above, may 

 be represented by the epiphysial bar of Amiurus. 



Concerning this region in the Polypterus chondrocranium, Budgett (1900) 

 says : "The lateral walls of the cranium extend forward from the auditory region 

 on either side of the ahsphenoid region as continuous vertical plates of carti- 

 lage, somewhat dumb-bell shaped in section and perforated by foramina for 

 the III, V, and VII nerves in the thinner middle portion. In the spheneth- 

 moid region there is a large lateral fontanelle closed only by membrane through 

 which passes the optic nerve, while above and below this membranous portion 

 there pass the thickened upper and lower cartilaginous borders of the cranial 

 wall, connecting on either side the ethmoid region with the posterior region 

 of the cranium. " 



Dorsally the ahsphenoid cartilages of the two sides in Pol)^terus are con- 

 nected with each other by a transverse cartilaginous bridge, which is placed 

 further back in the roof than the epiphysial bar in the cranium of Amiurus. 

 The general relations of the ahsphenoid cartilage to the cranial nerves in this 

 region are much the same as in the developing Acanthias, and are closer to 



