. Cunningham's Text-book of anatomy. Anatomy. 124 OSTEOLOGY. sagittal plane, is of variable size and form. The plane of its outlet differs somewhat in individual skulls; in most instances it is directed inferiorly and slightly forwards. Anteriorly the condyles encroach upon it, and narrow to some extent its transverse diameter. To its margins are attached the ligaments which unite it with the atlas'and epistropheus. Through it pass the lower part of the medulla oblongata where it becomes continuous with the spinal medulla, the two vertebral arteries, the accessory nerves, and the blood-vessels
. Cunningham's Text-book of anatomy. Anatomy. 124 OSTEOLOGY. sagittal plane, is of variable size and form. The plane of its outlet differs somewhat in individual skulls; in most instances it is directed inferiorly and slightly forwards. Anteriorly the condyles encroach upon it, and narrow to some extent its transverse diameter. To its margins are attached the ligaments which unite it with the atlas'and epistropheus. Through it pass the lower part of the medulla oblongata where it becomes continuous with the spinal medulla, the two vertebral arteries, the accessory nerves, and the blood-vessels of the meninges of the superior part of the spinal medulla. Connexions.—The occipital bone articulates with the two parietals in front and above, with the sphenoid in front and below, with the two temporals on either side, and with the atlas by means of its condyles. Ossification.—The major part of the bone ossifies in cartilage, the upper part of the squamous part (interparietal) alone developing in membrane. The basilar part begins to ossify about the sixth week of foetal life by the appearance of two centres, one in front of the other; the anterior, according to Albrecht, constitutes the basiotic, the posterior the basi-occipital. These two centres—which there is some reason to believe may themselves be formed by the fusion of pairs placed laterally—rapidly unite, so that the occurrence of one centre alone is frequently described. From this the fore part of the margin of the foramen magnum is formed, together with a portion of the anterior end of the occipital condyle on either side. It helps also to close up the front of the hypoglossal canal. Union with the condylic parts is complete about the fourth or fifth year. Ankylosis between the basi-occipital and the sphenoid takes place about the twenty-fifth year. The lateral, condylic, or exoccipital parts begin to ossify from a single centre about the end of the second month of foetal life. The notch for the hypogloss
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
