FOSSIL AND RECENT 101 



the trigeminal foramen. The latter foramen is situated anterior to the facial foramen 

 and separated from it by a narrow prefacial commissure. The absence of a separate 

 foramen for the profundus ciliaris leads one to suppose that it left the cranium with 

 the trigeminal trunk. The medial surface of the prootic is marked by two shallow 

 cups, adjacent to each of the foramina described above. These cups housed their 

 respective ganglia and they are the only evidence of a defined pars ganglionaris. 



Beneath the level of the pars jugularis the prootics are produced medially as a 

 horizontal platform, the prootic bridge. The abducens nerve passed through the 

 prootic bridge to the myodome. 



The autosphenotic is tetrahedral in shape, the apex directed laterally and somewhat 

 ventrally as a weakly developed autosphenotic spine. The otic ramus of VII 

 pierced the anterior face of the autosphenotic. The posterior face of this bone forms 

 the anterior wall of the deep dilatator fossa. 



The pterosphenoid is of irregular shape. It contacts the basisphenoid ventrally 

 and excludes the prootic from the optic foramen. Of the two foramina piercing the 

 pterosphenoid beneath the superficial ophthalmic groove the anterior may be identi- 

 fied as having transmitted the trochlearis. The posterior is probably the point 

 where the anterior cerebral vein left the cranial cavity. 



The basisphenoid, when viewed anteriorly, is ' Y ' shaped, the wings of the ' Y ' 

 contacting the prootic and pterosphenoid while the stem passes antero-ventrally, 

 expanding in the sagittal plane as it does so. The ventral contact with the para- 

 sphenoid was probably by cartilage. From near the top of the basisphenoid stem 

 a short prong of bone on either side passes ventro-laterally towards the myodome 

 opening. The significance of this structure is unknown, but it appears to be part 

 of the basisphenoid. It is also found in Osmeroides levis, 0. latifrons and in Tarpon 



(P- 50). 



In the dorsal half of the orbit the orbitosphenoid contacts the frontals dorsally 

 and the pterosphenoids posteriorly. Although clearly paired dorsally, the orbito- 

 sphenoids unite ventrally where they pass into a completely ossified interorbital 

 septum. The septum contacts the parasphenoid ventrally and the basisphenoid 

 posteriorly. The olfactory tracts passed out of the orbitosphenoid anteriorly. 



The lateral ethmoid forms the anterior wall of the orbit and the posterior and 

 outer wall of the nasal capsule. It is composed of transverse and lateral faces which 

 meet one another in a sharp ridge. This ridge is expanded laterally as a short spine. 

 Beneath the spine the lateral ethmoid is sutured with the expanded parasphenoid. 

 The transverse face of the lateral ethmoid meets the frontal dorsally. The un- 

 finished nature of the anterior margin of the lateral face suggests that the bone passed 

 into cartilage. Much of the ethmoid must have been cartilaginous, but a small area 

 of spongy bone lying above the anterior part of the vomer represents a restricted 

 mesethmoid. 



»The parasphenoid is stout and extends below most of the neurocranium. Anteriorly 

 it widens in the region of the lateral ethmoid but posteriorly beneath the otic capsule 

 it becomes narrower. The ascending wings of the parasphenoid are weakly developed. 

 The internal carotid foramen is at the base of the ascending wing. Beneath the 

 orbit the parasphenoid bears a large tooth plate which bifurcates anteriorly. The 



