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Cerebral Aqueduct
It varies in size from 0.40mm 2 to 9.48mm 2 (24 normal brains) according to Flyger and Hjelmquist.
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It varies in size from 0.40mm 2 to 9.48mm 2 (24 normal brains) according to Flyger and Hjelmquist.
The nerves that supply the heart usually converge anteriorly toward the lower part of the trachea but may be followed separately to the heart. Cardiac ganglia, varying in size and number, may occur along the cervicothoracic nerves that supply the aorta, pulmonary trunk, and arteries as well as the heart. Image 73A Image 73B Image 73C Image 73D Image 73E Image 73F
The following variations in the course and/or branches of this nerve have been reported. Instead of its usual course on the medial side of the temporal muscle, the nerve may pierce the muscle. When absent, the nerve is replaced by the posterior superior alveolar nerves. The buccal nerve may also arise from the inferior alveolar nerve, in which case it emerges from the inferior dental canal through a small foramen in the alveloar border of the mandible, just anterior to the ramus.
The brain usually weighs between 1200 and 1400 grams. It has been reported that the brain of Anatole France (French writer and Nobel Laureate) weighed 1040 gms. The brain weights (in grams) of some other notable individuals are: Ivan Turgenieff, (Russian novelist, dramatist, and short story writer) 2012; Georges Léopold Chrétien Cuvier (French zoologist and geologist) 1830; John Abercrombie, 1786; William Makepeace Thackeray (English novelist) 1658; Immanuel Kant (German metaphysician, philosopher) 1600; Spurzheim, 1559; Dirichlet, 1520; Daniel Webster, (American statesman, lawyer, and orator)…
The septum pellucidum may be absent. Agenesis of the septum pellucidum is often associated with agenesis of the corpus callosum, but either condition may occur without the other. When agenesis of the septum pellucidum is associated with hypoplasia of the optic disk, the condition is referred to as septooptic dysplasia. The septum may also be perforated.
In 70% of brains, the massa intermedia (interthalamic adhesion) forms a bridge of gray matter, which crosses the third ventricle and constitutes part of a bilateral nuclear complex. Reference Bruce, A. (1890) On the absence of the corpus callosum in the human brain with a description of a new case. Brain 12:171-190.
In a study of 200 brains, including a few mentally retarded individuals, paralytics, and a series of young fetuses, it was found that the left insula was more deeply marked by sulci than the right, and that its length, on average, was greater by 11 mm. The central sulcus of the insula is usually the first to appear developmentally, and it is more pronounced in males.
The fornix may be absent. Reference
The superior temporal sulcus is usually a continous sulcus but is occasionally separated into two or three sections, especially in the left hemisphere. The sulcus may encroach on the territory of the middle temporal sulcus. The terminal portion of the sulcus may be forked.
This sulcus may separate into two to six parts. It may interdigitate with the superior temporal sulcus.
The caudal extremity of the sylvian (lateral) fissure may be forked (41%) forming ascending and descending branches. The ascending branch is the most constant and is regarded as the true continuation of the fissure. The ascending branch forms the axis of the supramarginal gyrus. Triradiate termination of the sylvian fissure has been reported.
This sulcus may be formed by up to four different segments.
The precentral sulcus may be composed of two or three parts: precentral inferior, precentral medius, precentral superior. In about 17% of brains, the precentral sulcus does not show discontinuity into separate parts. The upper extremity of the precentral inferior sulcus may be located anterior to the lower end of the precentral superior sulcus or may unite with the latter forming a continuous sulcus. Occasionally, a horizontal ramus extends from the precentral inferior sulcus above the inferior frontal sulcus; this horizontal ramus may be confluent with the middle or superior frontal sulci.
This fissure may take a straight course or may assume a simple or an S-shaped curve.
In its simplest form, this sulcus is triradiate with an anterior branch (orbitalis anterior) and two posterior branches (orbitalis posterior and lateralis). The two posterior branches form a U-shaped furrow with a caudally directed concavity. A second anterior branch (orbitalis anterior lateralis) may be present lateral to the orbitalis anterior branch. The orbitalis anterior lateralis may join with the U-shaped furrow and with the orbitalis anterior forming an H-shaped configuration. The two longitudinal arms of the H-shaped pattern may separate to form two distinct sagittal furrows.
This sulcus usually bends medially at its rostral extremity, but it occasionally bends laterally. Its caudal extremity usually forks: the medial branch is short, while the lateral is usually long and bends anteriorly to hook around or anastomose with the posterior orbital sulcus.
The intraparietal sulcus may be formed by various combinations of its three phylogenetic components: a rostral vertical component, the postcentral inferior and superior sulci; a middle horizontal component, the intraparietal proper; and a caudal component, the paroccipital. The inferior and superior postcentral components may separate from the intraparietal sulcus proper and join the postcentral sulcus. The inferior postcentral sulcus may terminate in a forked fashion with the anterior branch directed toward the lower concavity of the central sulcus.
This may form a continuous furrow or be broken up into several parts. It is more constant than the inferior frontal sulcus. The posterior end of the sulcus may (64%) be connected with the superior precentral sulcus.
This sulcus is rarely uninterrupted. Its posterior end may be free or may join the middle or lower segment of the precentral sulcus.
The inferior frontal sulcus may be attached to the precentral inferior sulcus, or it may interrupted. It sometimes terminates in a bifurcation. The anterior part of the sulcus may be separated from the rest of the sulcus; the separated part is referred to as the lateral frontomarginal sulcus.