384 .PROF. T. JEITERT PAEKER ON THE CRANIAL OSTEOLOGY, 



iii. The base of the skull. (Plate LVI. fig. 2 ; Plate LVII. fig. 6 ; Plate LX. figs. 19, 

 21, & 22.) 



The basitemjwral platform [h. temp. pi.) is a prominent flattened elevation on the base 

 of the skull, having a nearly vertical posterior face separated by a deep groove, the 

 precondylar fossa (fig. 2, pr.confos.), from the occipital condyle ; in the fossa two pits, 

 probably venous, occur in Dinornis. The middle region of the posterior edge of the 

 platform is usually somewhat excavated, the excavation being bounded on either side 

 by a larger or smaller prominence, the mamillar tuberosity (Owen : basioccipital process, 

 Lydekker, mam.tub.), which forms the postero-lateral angle of the platform. Owen 

 considers these tuberosities to occur at the junction of the basisphenoid and basi- 

 occipital, but the examination of a young skull shows them to lie at the junction of 

 the basioccipital, exoccipital, and pro-otic (figs. 6, 7, & 14). About the posterior third 

 of the platform is formed by the basioccipital, the rest by the basitemporal underlying 

 the basisphenoid ; whether the basitemporal extends so far back as I have shown it in 

 fig. 6 is uncertain. 



Each mamillar tuberosity is separated from the corresponding paroccipital process by 

 ■a. deep paroccipital notch, immediately behind which occur one large and several small 

 foramina. The larger of these is the vagus foramen (precondyloid foramen, vagal 

 foramen, Owen, vag.for.) for the ninth and tenth nerves ; the smaller holes or condyloid 

 foramina {con for.) give exit to the twelfth nerve. The notch between the paroccipital 

 process and the mamillar tuberosity is sometimes converted into a foramen by a slender 

 bar of bone bridging it over. Immediately in front of it is the carotidj foramen 

 (fig. 6, car. for.), leading into the canal by which the carotid artery passes to the 

 pituitary fossa. In young skulls the greater part of the carotid canal is an open groove. 

 The antero-lateral angles of the basitemporal platform are formed by a pair of broad 

 projections, flattened from above downwards, the basipterygoid processes (b.pt.pr.) ; 

 they articulate by their distal ends with the pterygoid bones. Between the basi- 

 pterygoid process and the mamillar tuberosity, the lateral border of the platform is 

 obliquely furrowed by a deep groove for the Eustachian tube (figs. 2 & 6, eus.gr.). 

 The edges of the groove are often produced into roughened ridges, but these never 

 meet below so as to convert the groove into a tube ; in this respect the adult Moa 

 resembles the Kiwi at the time of hatching. 



In the centre of the basitemporal platform and between the inner ends of the 

 Eustachian grooves is usually to be found a more or less well-marked depression of 

 variable form — sometimes short and wide, sometimes long and narrow. At its posterior 

 end there frequently occurs a deep fossa, which in one young specimen was represented 

 by a foramen opening into the cranial cavity a short distance posterior to the pituitary 

 fossa. The aperture (fig. 6) is the posterior basicranial fontanelle (median venous 

 foramen, basisphenoid al mid-ventral canal, Owen, p.b.cr.fon.), marking the incomplete 

 concrescence of the parachordal cartilages of the embryo (24) ; the depression apparently 

 marks the incomplete extension mesiad of the basitemporal. 



