Page:Collier's New Encyclopedia v. 08.djvu/514

LEFT SKULL 450 SKULL generally pursuing smaller gulls and terns, and compelling them to drop or disgorge their prey. Four species visit the temperate regions of Europe and America: S. catarrhactes, the great skua, which breeds in the Shetland Islands; it is about 24 inches long, and of somber plumage; S. pomatorhinus, the pomato- rhine skua, 21 inches, dark mottled above, under surface brown (nearly white in old birds) ; S. crepidatus, the Arctic or Richardson's skua, about 20 inches long, occurring under two different plumages, one entirely sooty, the other with white under parts, and S. parasiticus, the long- tailed or Buffon's skua, about 14 inches long, upper part of head black, upper surface brownish-gray, under surface white. SKULL. The skull is divided into two parts, the cranium and the face. In human anatomy it is customary to de- scribe the former as consisting of eight and the latter 14 bones; the eight cranial bones, which constitute the brain case, being the occipital, two parietal, frontal, two temporal sphenoid and ethmoid ; while EUROPEAN SKULL the 14 facial bones, which surround the cavities of the mouth and nose and com- plete the orbits or cavities for the eyes, are the two nasal, two superior maxil- lary, two lachrymal, two malar, two palate, two inferior turbinated, vomer, and inferior maxillary. The bones of the ear, the teeth, and the Wormian bones are not included in this enumeration. The lower jaw articulates with the tem- poral bones by means of a diarthrodia joint, but all the others are joined by sutures. On the base of the cranium the occipital and sphenoid bones articulate by means of a plate of cartilage (syn- chondrosis) in young subjects; in adults this becomes bony union. Sutures are named from the bones between which they are found, but to those around the parietal bones special names are given — e. g., interparietal or sagittal; occipito- parietal or lambdoid; fronto-parietal or coronal; parieto-temporal or squamous. During adult life many of the sutures close by bony union and disappear, but. HUMAN SKULL a — Frontal bone b — Parietal bone c — Occipital bone d — Temporal bone e — Sphenoid bone f — Malar bone g — Nasal bone h — Upper jaw bone i — Lower jaw boi»e both the age at which this occurs and the order of its occurrence are subject to variation. Wormian bones are irregular ossifications found in relation to the su- tures of cranial bones, but these bones are seldom seen in relation to the bones of the face. The fact that concussion of the brain scarcely ever proves fatal, unless there NEGRO SKULL is also fracture of the skull, affords the most distinct evidence that the skull is constructed in such a manner that so long as it maintains its integrity it is able to protect its contents from serious lesion. There are two points in the archi- tecture of the bones of the face which deserve special notice — viz. (1) the great strength of the nasal arch; and (2) the