. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. ]48 ANATOIMY OF VEETEBRATES. very interesting: the end gained seems to be, in grovelling reptiles liable to have the head bruised, an extra protection of the epencephalon — the most important segment to life of all the ]irimary divisions of the cerebrospinal axis. The thickness of its immediately protecting walls (formed by the basi-, ex-, and super-occipitals) is equal to that of the same vertebral elements in the human skull; but they are moreover composed of very firm and dense tissue throughout, having no diploe: the
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. ]48 ANATOIMY OF VEETEBRATES. very interesting: the end gained seems to be, in grovelling reptiles liable to have the head bruised, an extra protection of the epencephalon — the most important segment to life of all the ]irimary divisions of the cerebrospinal axis. The thickness of its immediately protecting walls (formed by the basi-, ex-, and super-occipitals) is equal to that of the same vertebral elements in the human skull; but they are moreover composed of very firm and dense tissue throughout, having no diploe: the epen- cephalon also derives a further and equally thick bony covering from the basisphenoid and the parietals, the latter being partly overlapped by the mastoids, fig. 97, 8, which form here a third layer of the cranial wall. The basisi^henoid, fig. 96, 5, and presphenoid, 9, form a single 97. ^'^i'l^bkM^kkUI'Usi SkiiU t,i a Pytlion bone, and the chief keel of the cranial superstructure. The posterior articular surface looks obliquely upward and backward, and supjiorts that of the vertebral centrum behind, as the jJosterior ball of the ordinary vertebra?, su]iports the oblique cup of the succeeding one : here, however, all motion is between the two vertebra?, and the co-adapted surfaces arc rouiih and sutural. The basisphenoid presents a smooth cerebral cliannel above for the mesencephalon, in front of which a deep depression (sella) sinks abruptly into the expanded part of tlie bone, and tlicrc bifurcates, each fork forming a short cul-de-sac in the sub- stance of the bone. The transverse processes from tlic under and lateral surfaces are well marked, strong, but short, mucli thicker in the Python tlum in tlie Boa. Tlic alisphcnoids, «, form the anterior half of the fenestra ovalis, which is conqilcted by tlic exoccipitals; and in their two large perforations for the ])cisterior divisions of the fifth pair of nerves, as well as in their. Please note that these
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1860
