The exoocipitab (s, i) are very irregular subtrinnpuUr bones ; each U produced backwards 

 into a peduncular process supporting moiety of the upper half of the occipital condyle : at 

 the outer side of the bate of the peduncle U an obtuse process, forming the upper part of the 

 ridge continued upon the basioccipital. The outer and fore part of the exoccipiul expand* 

 into the irregular base of the triangle, U perforated by a ilit for the eighth pair of nerve*, 

 I below with the basioccipital. it excavated in front to lodge the petronl cartilage 

 it articulate* with the alisphenoid, and unite* above with the uperoccipital. The 

 Mptroceipiul () i* of a *ubrhomboidal form, tend* a *pine from iu upper and hinder surface, 

 expand* laterally into oblong processes, is notched anteriorly and tend* down two thin pUte* 

 from it* under surface, bounding on the meaial side the surface for the cerebellum, and by 

 the outer tide forming the inner and upper part* of the acoustic cavitir*. The suporocri- 

 piul articulate* below with the rxoccipiul* and aluphenoidi, and in front with the parietal, 

 by which it is overlapped in it* whole extent. The occipital vertebra i* a* if it were sheathed 

 in the expanded posterior outlet of the parieUl one, the centrum resting on the oblique sur- 

 face of that in front, and the anterior base of the neural (pine entering a cavity in and bring 

 overlapped by that of the preceding neural *pine : the analogy of this kind of ' emboitcmcnt ' 

 of the occipital in the parietal vertebra with the firm interlocking of the ordinary vertebrae 

 of the trunk U very interesting : the end gained seem* to be, chiefly, an extra protection of the 

 psneephalon the most hnporUuit segment to life of all the primary division* of the eerebro- 

 spinal axis. The thickness of iu immediately protecting wall* (formed by the bad-, ex- and 

 snper-oeoipitals) i* equal to that of the same vertebral element* in the human skull, but they 

 are inoreorer composed of very firm and dense ti*sue throughout, having no diploc : the 

 epenesphalon also derive* a further and equally thick bony covering from the basisphcnoid 

 and the parietal*, the latter being overlapped by the mastoids, which form a third covering 

 to the cerebellum. 



The basisphenoid (s) and presphrnoid () form a single bone, and the chief keel of the 

 . cranial *uper*tructure. The posterior articular surface look* obliquely upward* and back- 

 ward*, and support* that of the vertebral centrum behind, as the posterior ball of the ordi- 

 nary vertebra support* the oblique cup of the succeeding vertebra; : here, however, all motion 

 it abrogated between the two vertebrae, and the co-adapted surfaces are rough and sutural. 

 The hatitphnuisri present* a smooth cerebral channel above for the mesencephalon, in front 

 of which a deep dqustinn (tella) sink* abruptly into the expanded part of the bone, and 

 there bifurcates, each fork forming a abort cul-de-sac in the substance of the bone. The 

 traiuvene processes from the under and lateral surfaces are well-marked, strong, but short, 

 much thicker in the Python than in the Boa : a sharp ridge is produced from the middle of 

 the under surface of the basisphenoid : the under surface of the presphenoidal prolongation 

 is smooth and convex. 



The alisphenoid* (s) form the anterior half of the fenestra ovalis, which i* completed by the 

 exoceJpitals ; and in their two large perforations for the posterior division* of the fifth pair of 

 nerves, as well a* in their it latin sue and position, the alisphenoids agree with those of the 

 Frog. Each alisphenoid is a thick snboval piece, with a tubercular process on it* under and 

 lateral part: it rests upon the hssiephrnoid and basioccipiul. support* the posterior part of the 



