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The anterior end of the collateral fissure may be continuous with the rhinal fissure or with the anterior segment of the inferior temporal sulcus. The posterior end of the collateral fissure occasionally bifurcates into Y- or T-shaped branches
The cingulate sulcus may show partial or complete interruption in 28-50% of brains. The subcallosal portion of the sulcus may be doubled or tripled. In some cases the marginal ramus passes upward over the superomedial border to the dorsolateral surface.
Usually, the central sulcus presents two anterior convexities, but occasionally, four or five may occur. The upper half of the sulcus may turn sharply backward. The upper end of the sulcus usually cuts the dorsal border of the brain and turns caudally; rarely, it ends as much as 1 cm from the dorsal border. The upper third of the sulcus is frequently separated from the rest of the sulcus. The lower part of the sulcus may be directed forward and may unite with the subcentral anterior sulcus.
This fissure may be hook-like. Its anterior part may show one or several side branches pointing backward and downward, and its posterior part may be interrupted or may extend to the dorsolateral surface of the hemisphere.
The corpus callosum may be partially or completely absent or poorly formed.
The cerebral hemispheres may be asymmetric. The brain may be incompletely or imperfectly divided into two hemispheres. Cerebral heterotopia may result in abnormal functions. Image 09A Image 09B
The cavum vergae is the posterior extension of the cavum septi pellucidi. It is also called the sixth ventricle, which is a misnomer because the cavum does not contain cerebrospinal fluid nor is it lined by ependyma. The cavity was first described by the Italian anatomist, Andrea Verga, in 1851. It may exist as a separate cavity rather than communicating with the cavum septi pellucidi. The incidence of the cavum vergae was 2.3% in 1032 brains. Verga's ventricle is present in 1-9% of human brains and was described by Verga in 1851 according to Lang (1983).
The cavum veli interpositi is located in front of the quadrigeminal (superior) cistern above the roof of the third ventricle. It develops as a result of abnormal separation of the limbs of the Fornix. In one study, the cavum veli interpositi was found in 13 of 1200 (1.1%) pneumoencephalograms, and in another study, in 53 of 158 (30) patients less than two years old.
The septum pellucidum normally has a cavity of 1 to 2mm in width. When this cavity is larger, it is called cavum septi pellucidi or fifth ventricle. The term fifth ventricle is a misnomer because unlike ventricular cavities it does not contain cerebrospinal fluid nor is it lined by ependyma. The incidence of cavum septi pellucidi was 20.3% in 1032 brains studied. The cavurn septi pellucidi varies from 2 to 95% depending to author; it is more prevalent in the young (infants) than older adults. The extreme differences in the reported frequency is highly suspect.
Heterotopias of white matter within the medulla oblongata have been described. The left pyramid decussates first in about 73% of individuals. Interesting variations in the pyramidal tracts have been reported. In about 71% of 144 specimens, both crossed and uncrossed pyramidal tracts were present bilaterally. In 13%, only crossed tracts were present; in 12%, both crossed tracts and one uncrossed tract were present; in 2.8%, only uncrossed tracts were found; and in 0.7%, one pyramid was totally crossed, and the other pyramid was totally uncrossed.
There are a number of variations in the formation, course, and distribution of this nerve. It may have a root from the seventh cervical nerve by way of the lateral cord. It may be derived from the eighth cervical nerve only or from both the seventh and eighth cervical nerves. The ulnar may pass in front of the medial epicondyle of the humerus or lie behind the condyle. Connecting branches with the median nerve have been reported in the arm, forearm and hand. Other connecting branches with the medial brachial cutaneous and radial nerve have also been described.
This nerve may arise solely from the seventh cervical nerve, or from the seventh and eighth. It may also receive an additional branch from the sixth cervical nerve. This nerve is also known as the middle subscapular nerve. Image 31A Image 31B Image 31C Image 31D Image 31E Image 31F Image 31G Image 31H Image 31I Image 31J
Several variations in the formation, course, and distribution of this nerve have been reported. It may receive fibers from the fourth cervical nerve (50% of cases), in addition to those usually supplied by the fifth and sixth cervical nerves. The suprascapular nerve may arise entirely from the fifth cervical nerve. In some cases, it divides into two parts, an upper and a lower; the upper passes through or above the suprascapular notch (transverse ligament) and the lower passes through a foramen below the notch. The entire nerve may also pass over the transverse scapular ligament.
The following variations have been reported in these nerves. A branch to the phrenic nerve may pass down into the thorax over the subclavian artery or vein before joining the phrenic nerve. An additional bundle from the fifth cervical nerve joining this branch has been reported. A branch to the rhomboid muscles may pass through the trapezius muscle on its way to the skin close to the midline, at the level of the spinous processes of the fifth and sixth thoracic vertebrae. In 10 of 254 cases, the clavicle was perforated by the middle branch of the supraclavicular nerves.
The upper trunk of these nerves (upper subscapular) may arise from either the fifth or sixth cervical nerve instead of from both. The fourth cervical may also contribute. The middle (thoracodorsal) may arise solely from the fifth or seventh, or from the seventh and eighth cervical nerves. The lower subscapular nerve may arise from the fifth or sixth, or from the sixth and seventh cervical nerves. The nerve supply to the lower part of Mm. subscapularis and teres major (ordinarily from the lower subscapular) sometimes proceeds separately from the brachial plexus. The branch to m.
The radial nerve may accompany the axillary (circumflex) nerve through the quadrangular space (bounded by mm subscapularis and teres minor above, teres major below, the humeral head of the triceps medially, and the humerus laterally). The radial nerve may communicate with the ulnar nerve in the arm.
The posterior interosseous nerve may pass over instead of perforating the supinator muscle. It may supply the anconeus muscle, extensor carpi radialis brevis (36% of cases), and the opposed surfaces of the middle and index fingers. The posterior and anterior interosseous nerves sometimes communicate.
The medial pectoral (from the medial cord of the brachial plexus) may supply twigs to the clavicular head of the deltoid muscle and the acromioclavicular articulation. The lateral pectoral (from the lateral cord of the brachial plexus) may not receive fibers from the first thoracic nerve. Cutaneous branches from the lateral pectoral nerve have been described supplying the skin of the mammary region and axilla. Fibers from the medial pectoral nerve that supply m. pectoralis major may wind around the lower border of pectoralis minor instead of piercing it.
The nerve to subclavius (C5) may supply a branch to the phrenic nerve (accessory phrenic nerve). It joins the phrenic nerve either at the root of the neck or less frequently in the thorax. Rarely, the entire phrenic nerve arises from this branch, in which case it crosses the third part of the subclavian artery. A branch may communicate with the lateral and medial pectoral nerves, and another may supply the clavicular head of the sternocleidomastoid muscle. Image 31A Image 31B Image 31C Image 31D Image 31E Image 31F Image 31G Image 31H Image 31I Image 31J
The following variations in the formation, course, and distribution of this nerve have been reported. The combination from the first thoracic nerve to the formation of the median nerve may be missing. Either the outer (lateral) or the inner (medial) branch (from the lateral and medial cords) of the nerve may consist of two nerve bundles. The site of union between the lateral and medial branches is quite variable and has been found as far down as the elbow. The two branches may enclose the axillary vein as well as the axillary artery.