Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 276 .MAMMALIA. of the skull in place of the interorbital septum extend forward into the ethmoid region. Thus it happens that the ethmoid (lamina cribrosa] constitutes the boundary of the anterior and lower part of the skull (fig. ). The temporal bones also take an essential part in bounding the cranial cavity, since not only the petrous and a part of the rnastoid,* but also the large squamosal occupy the space remaining between the alisphenoids and exoccipitals. The occipital always
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 276 .MAMMALIA. of the skull in place of the interorbital septum extend forward into the ethmoid region. Thus it happens that the ethmoid (lamina cribrosa] constitutes the boundary of the anterior and lower part of the skull (fig. ). The temporal bones also take an essential part in bounding the cranial cavity, since not only the petrous and a part of the rnastoid,* but also the large squamosal occupy the space remaining between the alisphenoids and exoccipitals. The occipital always articulates with the first cervical vertebra (atlas) by two coiidyles, and its lateral portions (exoccipitals) frequently present a pyramidal process on each side (juyular or paramastoid process), The praesphenoid and basisphenoid (tig. fiG8) often remain separate No. 01 FIG 6G8.—Median longitudinal section of sheep's skull, from inside. Ob, Basi-occipital Ol, exoccipital; O*, supra-occipital; Pe, petrous; Spl, basi-sphenoid; Ps, pras- sphenoid ; Als, alispheuoicl; Orn, orbito-sphenoid ; Pa, parietal; Fr, frontal; Sf, frontal sinus ; EfTt, ethmoid; Na, nasal; C, ethmoturbinal; Ci,inferiorturbinal; Ft, pterygoid; Pal, palatine ; To, vomer ; , maxillary ; Jmx, prsemaxillary. for a long time. To the latter are applied the alisphenoids with the parietals, which belong to this region. An interparietal is often developed behind the parietal; it is, however, usually ankylosed with the supra-occipital, more rarely with the parietal. The frontal bones constitute the roof of the skull in the region of the orbitosphenoids; they are less frequently fused than are the parietals. The temporal bone has several constituents—(1) The petrous portion, which is composed of the three pieces of the periotic capsule—the pro-, opistho-, and epiotic ; (2) the mastoid portion, which is a part of the epiotic; (3) the squamous portion or squamosal, which is a larger bony scale; (4) the tympan
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