Substantia Perforata

SUBSTANTIA PERFORATA, also known as lamina perforata, or perforated substance. There are two such substances—anterior and posterior, which differ in location and significance.

Figure 1. Substantia perforata anterior of the base of the brain: 1 - bulbus olfactorius et tractus olfactorius; 2 - stria olfactoria medialis; 3 - stria intermedia; 4 - stria lateralis; 5 - nervus opticus; 6 - chiasma opticum; 7 - tractus opticus; 8 - substantia perforata anterior; 9 - pulvinar; 10 - trigonum lemnisci; 11 - nervus trochlearis; 12 - nervus trigeminus; 13 - nervus oculomotorius; 14 - substantia perforata anterior; 15 - gyrus rectus. Substantia perforata anterior... Figure 2. Substantia perforata posterior in the fossa interpeduncularis: 1 - nervus opticus; 2 - chiasma opticum; 3 - tractus opticus; 4 - nervus oculomotorius; 5 - corpus geniculatum laterale; 6 - corpus geniculatum mediale; 7 - pons Varolii; 8 - pedunculus cerebri; 9 - pulvinar; 10 - substantia perforata posterior; 11 - corpus mamillare; 12 - tuber cinereum; 13 - infundibulum. Substantia gyri perforati rhinencephali (Retzius), or area olfactoria, the anterior perforated substance, belongs to the olfactory lobe (lobus olfactorius, the peripheral part of the rhinencephalon), forming its posterior part. This lobe is atrophied in man, but well developed in many animals (especially rodents and carnivores); the phylogenetically oldest anterior perforated substance lies on the inferior surface of the brain, in a flat depression called the lateral cerebral vallecula (vallecula cerebri lateralis), behind the olfactory trigone (trigonum olfactorium), lateral to the optic chiasm, anterior to the second cranial nerve, and medial to the temporal lobe and the beginning of the Sylvian fissure (Fig. 1).

It has a quadrilateral shape, covered by a mass of openings for blood vessels; they are especially numerous in the anterior part adjacent to the trigone, which actually forms the anterior perforated substance, while the posterior part—the diagonal gyrus (gyrus diagonalis, Broca's diagonal band)—has a smoother surface. A portion of the secondary olfactory fibers, the middle olfactory stria, terminates in the anterior perforated substance. In animals, the anterior perforated substance consists of three layers: molecular, pyramidal, and polymorphic; the pyramidal layer is characterized by the presence of "olfactory islets"—clusters of small cells. In humans, this substance is very weakly developed. A disease syndrome of the anterior perforated substance has not been isolated. The posterior perforated substance is a connective tissue plate dotted with numerous openings serving for the passage of vessels; it forms the floor of Tarin's interpeduncular fossa (fossa interpeduncularis Tarini), located between the cerebral peduncles. By a shallow groove running along the middle, the posterior perforated substance is divided into two symmetrical halves; externally, in the direction of the cerebral peduncle, it is bounded by a groove—the oculomotor nerve sulcus (sulcus nervi oculomotorii), from which the fibers of the third cranial nerve emerge (Fig. 2).