82 MAEINE EEPTILES OF THE OXFOED CLAT. 



two posterior (XII.) probably transmitted branches of the hypoglossal nerve; the 

 hindermost is the larger and its outer opening is at the posterior end of the deep 

 groove beneath the base of the paroccipital process {p-P-)- In front of these 

 foramina there is on the inner face of the bones a large funnel-shaped aperture 

 {jug-), opening externally at the anterior end of the above-mentioned groove. 

 This aperture corresponds with the so-called jugal foramen of Siebenrock * and 

 transmitted the vagus group of nerves. It lies between the exoccipital and the 

 opisthotic elements, the latter in this case sending -down a process which fuses 

 with the exoccipital beneath the foramen and meets the basioccipital ^s above 

 described. According to Siebenrock f the opisthotic has a similar articulation with 

 the basioccipital in Ilatteria, but this is denied by Osawa J. 



Above and a little in front of the jugular foramen, and separated from it by a sharp 

 ridge forming the hinder edge of the opisthotic, there is a deep rounded fossa (a.) 

 for the ampulla of the posterior vertical semicircular canal [p.v.c), the channel for 

 which passes outwards and upwards from the inner end of the fossa, opening on 

 the upper surface by which the bone unites with the supraoccipital [soc.f.). Another 

 passage also runs outwards and forwards from the fossa and opens on the surface 

 for union with the pro-otic ; this is the channel for the horizontal semicircular 

 canal (h.c). The upper end of the combined exoccipital and opisthotic bears a large 

 flattened ovate surface for union with the supraoccipital (soc.f.) ; this facet, which 

 looks directly upwards, is mostly boi-ne by the opisthotic and, as mentioned above, 

 is perforated for the passage of the posterior vertical semicircular canal (p.v.c). 

 Anteriorly the opisthotic bears another facet (pro.f.) looking upwards and forwards, 

 making an angle of about 60° with the supraoccipital surface ; this facet is for union 

 with the pro-otic, and is perforated by the channel of the horizontal semicircular 

 canal {h.c). 



The outer face of the combined bones is somewhat flattened superiorly, while 

 its lower portion bears the greatly elongated paroccipital, the base of which extends 

 across the anterior two-thirds of the bone, being probably entirely borne by the 

 opisthotic. The process itself is directed downwards and backwards ; it narrows 

 somewhat in the middle, but expands distally and terminates in a roughened convex 

 facet (§'./'.), by which no doubt it articulates with the quadrate, although no specimen 

 showing the actual junction has been observed. Beneath the base of the 

 paroccipital process is a deep groove, at the posterior end of which is the outer 

 opening of the passage for the XII. nerve, while at the anterior end is the jugular 



* Siebenrocli, " Zur Anatomie des HaiUria-Kopies," Sitz. Akad. Wissensch. "Wien, vol. cii. pt. i. (1893) 

 p. 256. 



t Ojp. cit. p. 250. 



t Osawa, "Beitrage zur Anatomie des Hattena punctata" Arch. f. Iklikroskop. Anatomie, vol. li. 

 (1897-S) p. 495. 



