. On the anatomy of vertebrates [electronic resource] . this fissure. A horizontalseptum divides an upper from a lower compartment of the anteriorhalf of the tympanic bulla. The sella turcica is shallow, and notdefined by clinoid processes; the chiasmal platform is subqua-drate, and leads to a fossa, perforated by the two large and ap-proximated elliptical optic foramina; a deep and narrow grooveextends from the optic fossa to the rhinencephalic compartment,where it divides to terminate at the orbito-ethmoidal foramina. The foramen rotundum andforamen lacerum anteriuscombine to form a largesub
. On the anatomy of vertebrates [electronic resource] . this fissure. A horizontalseptum divides an upper from a lower compartment of the anteriorhalf of the tympanic bulla. The sella turcica is shallow, and notdefined by clinoid processes; the chiasmal platform is subqua-drate, and leads to a fossa, perforated by the two large and ap-proximated elliptical optic foramina; a deep and narrow grooveextends from the optic fossa to the rhinencephalic compartment,where it divides to terminate at the orbito-ethmoidal foramina. The foramen rotundum andforamen lacerum anteriuscombine to form a largesubquadrate vacuity. Thecerebellar fossa on the upperpart of the petrosal is verydeep. The meatus internusis extremely shallow, andalmost immediately dividesinto the cochlear and vesti-bular canals. In the Porcupine{Hystrixcristata), fig. 238, the occi-pital region is nearly fiat; the paroccipitals descend only to the levelof the occipital condyles. The mastoid forms but a rough auditory bulla? are moderately developed ; the external meatus 238. Skull of the Porcupine. SKELETON OE RODENTIA. 373 is shorty directed outward and a little forward, and is notchedbehind. A fissure, which widens at both ends, divides the tympanic from the clamping process of the squamosal: this articulatesbehind by a suture with the mastoid. The parietals, fig. 239, 7, arebroad, but short, and pinched in, as it were, by the temporal fossa?,which almost meet at the line of the sagittal suture, which is obli-terated. The frontals, ib. n, are more than double the size of theparietals, and are greatly swollen by the enormous sinuses. Themost remarkable feature of the Porcupines cranium is the magni-tude of the nasal bones, 15, especially their great posterior expanse,which terminates behind on the same vertical parallel as the middleof the zygomatic arch. This character is contrasted in fig. 239with the small size of the nasals, 15, in the Manatee and CapuchinMonkey. The thick anterior pier by which
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