Fissura

When two are present, they are generally situated one above the other, the upper being the larger; the second piece has seldom more than one; the third, fourth, and fifth pieces are often formed from two centers placed laterally, the irregular union of which explains the rare occurrence of the sternal foramen (Fig. 121), or of the vertical fissure which occasionally intersects this part of the bone constituting the malformation known as fissura sterni; these conditions are further explained by the manner in which the cartilaginous sternum is formed. ❋ Unknown (1918)

The inferior orbital fissure (fissura orbitalis inferior; sphenomaxillary fissure), horizontal in direction, opens into the lateral and back part of the orbit. ❋ Unknown (1918)

The petrotympanic fissure (fissura petrotympanica; Glaserian fissure) opens just above and in front of the ring of bone into which the tympanic membrane is inserted; in this situation it is a mere slit about 2 mm. in length. ❋ Unknown (1918)

The Anterior Median Fissure (fissura mediana anterior; ventral or ventromedian fissure) contains a fold of pia mater, and extends along the entire length of the medulla oblongata: it ends at the lower border of the pons in a small triangular expansion, termed the foramen cecum. ❋ Unknown (1918)

The Posterior Median Fissure (fissura mediana posterior; dorsal or dorsomedian fissure) is a narrow groove; and exists only in the closed part of the medulla oblongata; it becomes gradually shallower from below upward, and finally ends about the middle of the medulla oblongata, where the central canal expands into the cavity of the fourth ventricle. ❋ Unknown (1918)

At the front part of the auricula, where the helix bends upward, is a small projection of cartilage, called the spina helicis, while in the lower part of the helix the cartilage is prolonged downward as a tail-like process, the cauda helicis; this is separated from the antihelix by a fissure, the fissura antitragohelicina. ❋ Unknown (1918)

The best marked of the early fissures are: (a) the fissura prima between the developing culmen and declive, and (b) the fissura secunda between the future pyramid and uvula. ❋ Unknown (1918)

The Hippocampal Fissure (fissura hippocampi; dentate fissure) begins immediately behind the splenium of the corpus callosum, and runs forward between the hippocampal and dentate gyri to end in the uncus. ❋ Unknown (1918)

The Longitudinal Cerebral Fissure (fissura cerebri longitudinalis; great longitudinal fissure) contains a sickle-shaped process of dura mater, the falx cerebri. ❋ Unknown (1918)

The Calcarine Fissure (fissura calcarina) (Fig. 727) is on the medial surface of the hemisphere. ❋ Unknown (1918)

The Parietoöccipital Fissure (fissura parietoöccipitalis). ❋ Unknown (1918)

The Lateral Cerebral Fissure (fissura cerebri lateralis [Sylvii]; fissure of Sylvius) (Fig. 726) is a well-marked cleft on the inferior and lateral surfaces of the hemisphere, and consists of a short stem which divides into three rami. ❋ Unknown (1918)

The Collateral Fissure (fissura collateralis) (Fig. 727) is on the tentorial surface of the hemisphere and extends from near the occipital pole to within a short distance of the temporal pole. ❋ Unknown (1918)

The Anterior Median Fissure (fissura mediana anterior) has an average depth of about 3 mm., but this is increased in the lower part of the medulla spinalis. ❋ Unknown (1918)

The _fissura calcarina_ has its origin directly on the surface of the occipital lobe, does not receive until late the _fissura parieto-occipitalis_, and goes directly, on the right side, into the _fissura hippocampi_. ❋ William T. Preyer (1869)