Anterior Perforated Substance Research Articles

Anatomia microcirúgica da substâcia perfurada anterior basal humana

The anterior perforated substance (APS) is a landmark in the basal forebrain. It has a basal face located above the carotid bifurcation in the subarachnoid space, and an interhemispheric one. It is the site of passage of the arteries to the caudate nucleus, putamen, internal capsule, adjacent areas of the globus pallidus and thalamus. Fifty hemispheres from twenty-five adult cadavers were obtained. The arteries were perfused with colored latex, Batsons resin and gelatin colored with carmine. Using a surgical microscope we have determined the origin, local and number of origin from the parent vessel. The sites of penetration in the mediolateral and anteroposterior direction were also recorded. The anterior communicating artery contribution to the basal APS was reviewed. Significant vascular variations and anastomoses were encountered mainly involving middle cerebral and anterior choroidal arteries. The precise understanding of these vessels has surgical and clinical implications in the management of vascular and tumoral maladies related to the anterior perforated substance.

Microsurgical anatomy of the insula and the sylvian fissure.

The purpose of this study was to define the topographic anatomy, arterial supply, and venous drainage of the insula and sylvian fissure. The neural, arterial, and venous anatomy of the insula and sylvian fissure were examined in 43 cerebral hemispheres. The majority of gyri and sulci of the frontoparietal and temporal opercula had a constant relationship to the insular gyri and sulci and provided landmarks for approaching different parts of the insula. The most lateral lenticulostriate artery, an important landmark in insular surgery, arose 14.6 mm from the apex of the insula and penetrated the anterior perforated substance 15.3 mm medial to the limen insulae. The superior trunk of the middle cerebral artery (MCA) and its branches supplied the anterior, middle, and posterior short gyri; the anterior limiting sulcus; the short sulci; and the insular apex. The inferior trunk supplied the posterior long gyrus, inferior limiting sulcus, and limen area in most hemispheres. Both of these trunks frequently contributed to the supply of the central insular sulcus and the anterior long gyrus. The areas of insular supply of the superior and inferior trunks did not overlap. The most constant insular area of supply by the cortical MCA branches was from the prefrontal and precentral arteries that supplied the anterior and middle short gyri, respectively. The largest insular perforating arteries usually arose from the central and angular arteries and most commonly entered the posterior half of the central insular sulcus and posterior long gyrus. Insular veins drained predominantly to the deep middle cerebral vein, although frequent connections to the superficial venous system were found. Of all the insular veins, the precentral insular vein was the one that most commonly connected to the superficial sylvian vein.

Microsurgical anatomy of the early branches of the middle cerebral artery: morphometric analysis and classification with angiographic correlation.

The cortical arteries arising from the main trunk of the middle cerebral artery, proximal to its bifurcation or trifurcation, are called "early branches." The purpose of this study was to characterize these early branches. The early branches were characterized according to their sites and patterns of origin, diameters, and relative proximity to the internal carotid artery bifurcation, as well as the course and area of supply of their cortical branches based on an examination of 50 hemispheres. Special attention was directed to the perforating arteries that arose from the early branches and entered the anterior perforated substance. The anatomical findings were compared with data obtained from 109 angiograms. Early branches directed to the temporal and frontal lobes were found in 90 and 32% of the hemispheres, respectively. The early branches that arose more proximally from the M1 segment were larger than those arising distally. Lenticulostriate arteries arose from 81% of the early frontal branches (EFBs) and from 48% of the early temporal branches (ETBs). An average of two cortical arteries arose from the EFBs and 1.3 from the ETBs, the most common of which supplied the temporopolar and orbitofrontal areas. Although the microsurgical anatomy of the early branches demonstrates abundant diversity, they can be classified into clearly defined patterns based on anatomical features. These patterns can prove helpful in evaluating angiographic data and in planning an operative procedure.

The paleocortical ventricle is the origin of reelin-expressing neurons in the marginal zone of the foetal human neocortex.

The subpial granular layer (SGL) is a transient cell layer in the cortical marginal zone during the period of neuronal migration into the cortical plate. The origin of the SGL has been studied by immunocytochemistry for calretinin (CR) and reelin in human foetuses from 11 to 40 gestational weeks (GW). At 11 GW, the paleocortical ventricle, a rostral dilatation of the lateral ventricle, gives rise to two fountainheads: a medial fountainhead provides neurons for the marginal zone (MZ) of the rostral cortex and rostral hippocampal rudiment, while multiple cell streams migrate from a lateral fountainhead into the MZ of the paleocortex and insula. The latero-medial gradient of neuronal packing density in the neocortical MZ indicates that migration extends farther into the neocortex. Neurons express CR already in the retrobulbar ventricular zone; they express reelin only as they approach the MZ of the paleocortex and rostral archicortex. At 16/17 GW, large numbers of CR-immunoreactive granule cells originate from the same fountainheads, and then direct medially, toward the surface of the anterior perforated substance, and laterally, into the paleocortical MZ, from where they continue into the neocortical SGL following a ventrolateral to dorsomedial gradient. From 13 to 18 GW, reelin is expressed by a subpopulation of granule cells and by Cajal-Retzius-like neurons. By 22 GW, the paleocortical ventricle undergoes regression and no longer supplies the SGL. Our results show that the paleocortical ventricle gives rise to a stream of neurons which extends over the cortical MZ as the subpial granular layer. The fact that SGL derivatives express reelin suggests that this transient cell layer may play a significant role in the establishment of the complex cytoarchitecture of the cerebral cortex.

Microsurgical anatomy of the short central artery

We studied the origin, length, external diameter, disposition, branching patterns and the perforators ofshort central artery in the circle of Willis in eighty fresh, unfixed cerebral hemispheres (40 brains). We also examined the relationship of the short central artery, the recurrent artery of Heubner, and M 1 perforators to the anterior perforated substance, caudate and putamen. The short central artery arises at 5.2 ± 3.36 mm from the origin of the anterior cerebral artery, hidden and overlapped by the internal carotid artery bifurcation. The recurrent artery ofHeubner arises distally to the origin of the short central artery. Four main anatomical variations were found: 1. Presence of short central artery and recurrent artery of Heubner (37.5±). 2. Isolated presence of the short central artery (27.5%). 3. Isolated presence of the recurrent artery of Heubner (21.25%). 4. Absence of short central artery and recurrent artery of Heubner (73.75%). Two different branching patterns were observed: 1. 2-4 straight perforators from the short central artery, perforators from the recurrent artery of Heubner and lenticulostriate from the most medial portion of the M 1, in 42 of 80 hemispheres (52.5%). 2. 8-10 perforators from only short central artery in 10 of 80 hemispheres (12.5%) with absent or hypoplastic recurrent artery of Heubner and lenticulostriates from M1 and M2. [Neural Res 1998; 20: 209-217]

Dilated Virchow-Robin spaces: MRI pathological study.

We performed a histopathological study of two human brains to look at dilated Virchow-Robin (V-R) spaces in the anterior perforated substance and putamen. We measured the diameter of 74 arteries in 54 dilated V-R spaces. In 28 patients without neurological deficits we ascertained the characteristic location of dilated V-R spaces in the anterior perforated substance and basal ganglia on MRI, measuring the distance from 64 foci of cerebrospinal fluid signal intensity to the centre of the mamillary body on 1 mm thick images. In the histopathological study, the mean diameter of the arteries was 39.0 +/- 36.0 microns. Dilatation of the V-R space was observed from the end of the indentation of the pial membrane towards the brain surface along the perforating artery. In the MR images, the mean distance from the dilated V-R space to the mamillary body was 10.0 +/- 4.5 mm. The V-R space was confined to a fixed level in the lower part of the basal ganglia, and not found near the brain surface.

Distribution of nitric oxide synthase in the central nervous system of Macaca fuscata: subcortical regions

The distribution of nitric oxide synthase-immunoreactive neurons was studied in the Macaca fuscata by immunohistochemistry using antiserum against nitric oxide synthase. In the macaque lower brainstem, many nitric oxide synthase-containing cell bodies were found in the gigantocellular and parvocellular reticular nuclei, the nucleus of the spinal tract of trigeminal nerve, the cochlear nucleus, the prepositus hypoglossi and the nucleus of the solitary tract. Many nitric oxide synthase-immunoreactive perikarya were observed in the laterodorsal-pedunculopontine tegmental nucleus complex of the macaque pontine and midbrain tegmentum. In addition, there were many highly immunoreactive cell bodies in the superficial layers of the inferior and superior colliculi. In the forebrain, numerous cell bodies were observed in the caudate nucleus, putamen, nucleus accumbens, nucleus of the diagonal band, anterior perforated substance and amygdaloid complex. Whereas most of these neurons were labeled highly intense for nitric oxide synthase, there were also many lightly labeled nitric oxide synthase-immunoreactive neurons in the substantia innominata, globus pallidus, ansa peduncularis and lateral hypothalamic nucleus. The present observation indicated some species difference in the distribution of central nitric oxide synthase-containing neurons. Furthermore, the present neuroanatomical evidence that nitric oxide synthase is distributed in a variety of specific neuronal systems, with some differences in the patterns of cytoplasmic localization, further indicates the neural messenger role of nitric oxide in the central nervous system.

Selective occlusion of blood supply to the anterior perforated substance of the dog: a highly reproducible stroke model

We created a highly reproducible stroke model in dogs by the selective occlusion of middle and anterior cerebral artery branches that penetrate the anterior perforated substance and supply much of the basal forebrain. We also analyzed the anatomic organization of the arterial supply to this region in this animal. Perforators came from anterior communicating artery branches similar to the recurrent artery of Heubner in humans and from the middle cerebral artery at several sites distal to the bifurcation of the internal carotid artery. Although some animals had a single source of the perforating arteries, most had two or more. In 50% of our specimens, the anterior communicating artery was the dominant source of arterial supply, in 21% the middle cerebral artery was dominant, and in 24% neither source dominated. Occlusion of all microscopically visible perforators to the anterior perforated substance reliably resulted in infarction of the internal capsule (100%), caudate nucleus (91%–100%), putamen or globus pallidus (82%–91%), and anterior commissure (73%). Structures involved less frequently in infarctions include the external capsule, claustrum, anterior commissure, and septal nuclei. We believe this anatomic information is useful for understanding why previous focal ischemia lesions in the distribution of the middle cerebral artery in the dog have been highly variable as well as for planning and interpreting future studies in this species. The proposed model of focal ischemia may be of use for the study of stroke.

The Terminal Nerve of Dolphins: Gross Structure, Histology and Luteinizing-Hormone-Releasing Hormone Immunocytochemistry

The terminal nerve (TN) of several dolphins was examined using gross dissection aided by osmium staining, routine light and electron microscopy, and immunocytochemistry with antibodies to mammalian luteinizing-hormone-releasing hormone (LHRH). The TN consists of numerous pial strands which emanate from large paired ganglia located in the dura near the frontal lobe of the hemisphere. The strands are largely composed of myelinated axons which extend to basal forebrain areas including the anterior perforated substance. Peripheral branches of the ganglia run through foramina in the ethmoid bone into the region of the nasal sacs and blowhole. Round to oval ganglion cells are scattered along the nerve and thousands of similar cells are found in the dural ganglia where they are encapsulated by satellite cells. A second, less prevalent cell type is also found in the ganglia. These neurons are fusiform, lack a well-defined capsule and are LHRH-immunoreactive. The results are compared to observations of the anatomy and functions of the TN in other mammals, which unlike toothed whales have retained an olfactory system. Involvement in reproduction and control of secretions and/or circulation of the nasal sac vocalization system are suggested functions of the TN in dolphins.

Microanatomy of the anterior cerebral artery

The microanatomic features of the anterior cerebral artery were studied in 30 unfixed human brains which were injected with tinted polyester resin via cannulation of the internal carotid arteries under microscopic dissection. The outer diameter, length, and number of perforating branches were measured for each of the following vessels: anterior cerebral artery (proximal A 1 segment, distal A2 segment), anterior communicating artery, and recurrent artery of Heubner. The perforating branches of the proximal segment of the anterior cerebral artery penetrated the brain at the anterior perforated substance, lateral chiasm, and optic tracts. The perforating branches of the anterior communicating artery penetrated the brain at the lamina terminalis, anterior perforated substance, and medial chiasm. The first 5 mm of the distal anterior cerebral artery (A2) had perforating branches penetrating the brain at the gyrus rectus and olfactory sulcus. The recurrent artery of Heubner originated from the A2 segment of the anterior cerebral artery in 57% of the cases, from the anterior cerebral artery-anterior communicating artery junction in 35%, and from the A1 segment in 8%. The depth of the interhemispheric fissure at the genu was 36.0 ± 0.5 mm and at the midbody of the corpus callosum, 35.0 ± 0.5 mm. Extension of the dissection to approach the anterior communicating artery from the genu of the corpus callosum using the anterior interhemispheric route was an additional 31.7 ± 0.7 mm. The callosal arterial supply from the anterior cerebral artery showed short callosal branches in all brain specimens and long callosal vessels in 10% of the specimens.

Distribution of central cholinergic neurons in the baboon (Papio papio). I. General morphology.

The morphological characteristics of cholinergic neurons in the central nervous system (CNS) of the baboon (Papio papio) were studied by choline acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) pharmacohistochemistry. The distributions of central cholinergic neurons as visualized by these two histochemical techniques were similar in most, but not all regions of the brain and spinal cord. Based upon these observations, central cholinergic neurons that are immunoreactive to ChAT and intensely stained for AChE by the pharmacohistochemical procedure can be divided into four major groups: (1) those in the caudate nucleus, putamen, nucleus accumbens and anterior perforated substance. These ChAT-containing and AChE-intense neurons are large and multipolar, and are scattered throughout these structures. (2) The rostral cholinergic column, which consists of a continuous mass of cholinergic perikarya situated in the medial septal nucleus, nucleus of the diagonal band, and nucleus basalis (Meynert). The ChAT-immunoreactive and AChE-intense cell bodies of the nucleus basalis are a prominent feature in the basal forebrain of the baboon. The labeled neurons are large, multipolar, and hyperchromic and show a tendency to aggregate in cell clusters. These cells are distributed within the full extent of the substantia innominata, often being associated with subcortical fiber networks such as the medullary laminae of the globus pallidus. (3) The caudal cholinergic column, which consists of a continuous group of cholinergic neurons in the caudal midbrain and pontine tegmentum. The rostral component of this group of cells is the nucleus tegmenti pedunculopontinus (subnucleus compacta) and it extends caudally to include the laterodorsal tegmental nucleus. Compared to that in other species the nucleus tegmenti pedunculopontinus in the baboon appears to occupy a relatively greater volume and is composed of a greater number of cholinergic neurons. The cells of the caudal column are large and hyperchromic. (4) Nuclei of origin of somatic and visceral efferents of the cranial nerves (III, IV, V, VI, VII, IX, X, XI, XII) and spinal nerves. In addition to these major cholinergic cell groups, a small population of ChAT-positive and AChE-intense cell bodies can be observed at the floor of the fourth ventricle and in lamina VII and X of the cervical cord. The present findings indicate that although some differences exist, the overall distribution and morphological features of cholinergic cell bodies identified in the baboon brain and spinal cord are similar to those demonstrated previously in investigations of the rhesus monkey and nonprimates.

Microsurgical anatomy of the anterior perforating arteries.

The anterior perforating arteries, the group of arteries that enter the brain through the anterior perforated substance (APS), were examined using X 3 to X 40 magnification in 50 cerebral hemispheres obtained from 25 adult cadavers. These arteries arose from the internal carotid, middle and anterior cerebral, and the anterior choroidal arteries. The carotid branches to the APS arose distal to the origin of the anterior choroidal artery. The anterior choroidal artery branches arose from the main or superior branch of the artery. The middle cerebral artery branches to the APS (the lenticulostriate arteries) arose from the M1 and M2 segments and were divided into medial, intermediate, and lateral groups, each of which had a characteristic configuration. The anterior cerebral artery branches arose from the A1 segment and from the recurrent artery. The internal carotid and anterior choroidal artery branches entered the posterior half of the central portion of the APS. The lenticulostriate branches entered the middle and posterior portions of the lateral half of the APS. The A1 segment gave rise to branches which entered the medial half of the APS above the optic nerve and chiasm. The recurrent artery sent branches into the anterior two-thirds of the full mediolateral extent of the APS. The relationship of these branches to the cerebral structures above the APS and to the common aneurysm sites is reviewed.

Microsurgical anatomy of the recurrent artery of Heubner.

The recurrent arteries of Heubner were studied in 30 unfixed human brains (60 hemispheres) obtained from routine autopsies of individuals with a mean age of 34 years. The arteries were injected with tinted polyester resin via cannulation of the internal carotid arteries, and dissected under microscopic magnification. The recurrent artery of Heubner was absent in two hemispheres and double in seven hemispheres, either with a separate origin (in two) or from a common stem (in five). The artery of Heubner had a mean outer diameter of 0.8 +/- 0.04 mm (range 0.3 to 1.5 mm) and a mean length of 23.4 +/- 1.1 mm (range 12 to 38 mm). It originated from the A2 segment of the anterior cerebral artery (ACA) in 57% of the specimens, from the junction of the ACA and the anterior communicating artery in 35%, and from the A1 segment of the ACA in 8%. Three types of recurrent courses were observed. In the Type I or superior course, seen in 41 (63%) of the 65 arteries, the artery followed the superior wall of the A1 segment of the ACA. In the Type II or anterior course, the arteries found in 22 (34%) of specimens maintained a rostral position in relation to the A1 segment. In the Type III or posterior course, taken by two (3%) arteries, a posterior course of the vessel in the anterior perforated substance was found. The branching pattern was identified down to a range of 100 to 200 mu, and the average number of branches was 6.5 +/- 0.4 (range 3 to 12). Four groups of branches were observed. The olfactory group was represented in 91% by a single olfactory branch, with a mean outer diameter of 0.3 +/- 0.03 mm. On average, 1.9 +/- 0.27 frontal branches were found with a mean diameter of 0.13 +/- 0.01 mm. The branches penetrating the anterior perforated substance had a larger outer diameter (mean 0.4 +/- 0.03 mm) with an average number of 2.5 +/- 0.2 branches. The Sylvian fissure branches were more numerous (mean 3 +/- 0.3) with a mean outer diameter of 0.4 +/- 0.03 mm. The point of penetration of the main trunk was found to be constant at the level of the lateral perforated substance-medial Sylvian fissure in 85% of the cases. This report emphasizes the advantages of the intravascular casting resin injection technique in unfixed human brains over other conventional methods. It also describes the application of these anatomic data to the surgical strategy for the anterior circle of Willis, including the possible use of the recurrent artery of Heubner for microvascular reconstructive procedures.

Microsurgical anatomy of the supraclinoid portion of the internal carotid artery.

The microsurgical anatomy of the supraclinoid portion of the internal carotid artery (ICA) was studied in 50 adult cadaver cerebral hemispheres using X 3 to X 40 magnification. The ICA was divided into four parts: the C1 or cervical portion; the C2 or petrous portion; the C3 or cavernous portion; and the C4 or supraclinoid portion. The C4 portion was divided into three segments based on the origin of its major branches: the ophthalmic segment extended from the origin of the ophthalmic artery to the origin of the posterior communicating artery (PCoA); the communicating segment extended from the origin of the PCoA to the origin of the anterior choroidal artery (AChA); and the choroidal segment extended from the origin of the AChA to the bifurcation of the carotid artery. Each segment gave off a series of perforating branches with a relatively constant site of termination. The perforating branches arising from the ophthalmic segment passed to the optic nerve and chiasm, infundibulum, and the floor of the third ventricle. The perforating branches arising from the communicating segment passed to the optic tract and the floor of the third ventricle. The perforating branches arises from the choroidal segment passed upward and entered the brain through the anterior perforated substance. The anatomy of the ophthalmic, posterior communicating, anterior choroidal, and superior hypophyseal branches of the C4 portion was also examined.

INCREASED DOPAMINE CONCENTRATION IN LIMBIC AREAS OF BRAIN FROM PATIENTS DYING WITH SCHIZOPHRENIA

Dopamine, noradrenaline, glutamate decarboxylase (GAD) and choline acetyl-transferase (CAT) were measured in post-mortem brain samples from more than 50 patients dying with a hospital diagnosis of schizophrenia and an equal number of controls. GAD was measured in 14 different brain regions, and was significantly lower in both control and schizophrenia patients who died following a protracted illness. If GAD values from patients who died suddenly were compared, no significant differences were observed between the control and schizophrenia groups. There was also no differences between the CAT values measured in 13 different brain regions in the two groups. Noradrenaline values were not different in the two groups in most limbic areas or in the caudate nucleus, but were elevated in the schizophrenic group in nucleus accumbens and in anterior perforated substance. These differences were not, however, statistically significant. On the other hand dopamine concentrations in nucleus accumbens and in anterior perforated substance were significantly elevated (by 34 and 95 per cent, respectively) in the schizophrenia group as compared with controls, although dopamine values were not different in caudate nucleus, putamen, septal nuclei or amygdala. The finding of elevated concentrations of dopamine in certain areas of the limbic forebrain in schizophrenia is discussed in relation to current hypotheses of the involvement of dopamine in this illness, and the difficulties of determining whether the observed changes are related to chronic treatment with antischizophrenic drugs.

Microsurgical anatomy of the anterior cerebral-anterior communicating-recurrent artery complex.

The microvascular relationships important to surgery of aneurysms in the anterior communicating region were defined in 50 cadaver brains. The recurrent artery of Heubner was frequently exposed before the A-1 segment in defining the neck on anterior cerebral aneurysms because it commonly courses anterior to A-1. It arose from the A-2 segment of the anterior cerebral artery (ACA) in 78% and most commonly terminated in the area of the anterior perforated substance, and lateral to it in the Sylvian fissure. The anterior communicating artery (ACoA) frequently gave rise to perforating arteries which terminated in the superior surface of the optic chiasm and above the chiasm in the anterior hypothalamus. This finding contrasts with previous reports that no perforating branches arise from the communicating artery. The proximal half of the A=1 segment was a richer source of perforating arteries than the distal half. The A-1 branches most commonly terminated in the anterior perforated substance, the optic chiasm, and the region of the optic tract. The ACoA increased in size as the difference in the diameter between the right and left A-1 segments increased. Frequent variants such as double or triple ACoA's, triple A-2 segments, and duplication of the A-1 segments were encountered. The clinical consequences of occlusion of the recurrent artery and of the perforators from the ACoA and medial and lateral segment of A-1 are reviewed.

Central reticular path to intralaminar and reticular nuclei of thalamus for activating EEG related to consciousness

Intralaminar nuclei include parafascicular, limitans, centrum medianum, central, paracentral and central lateral, all situated along the length of the internal medullary lamina of the dorsal thalamus. The reticular thalamic, tegmentothalamic and tectothalamic tracts end in these nuclei which give rise to fibers that go out to end in the reticular nucleus on the outer surface of the thalamus. The reticular nucleus sends non-specific fibers to all parts of the cerebral cortex. The parafascicular and nucleus limitans send fibers to the reticular nucleus from which fibers go to the occipital cortex. Centrum medianum, near its middle, sends fibers ventrally and out to the ventral part of the reticular nucleus. An intralaminar bundle of fibers comes out of the frontal end of centrum medianum and ends in the central, paracentral, central lateral and submedial nuclei. Large cells in the bundle send fibers ventrally and out to the lower part of the reticular nucleus. Central and paracentral nuclei send fibers in the internal medullary lamina to the central lateral nucleus. From this nucleus fibers pass over the lateral anterior nucleus to reach the dorsal margin of the reticular nucleus. Central, paracentral and submedial nuclei send fibers in the inferior thalamic peduncle to the anterior perforated substance, and also fibers forward to the reticular nucleus and frontal cortex. Some fibers cross in the massa intermedia. Ventral medial and ventral anterior nuclei send fibers into the frontal radiation to the reticular nucleus and visceral areas in the medial frontal, orbital, insular and inferior frontal cortex. Ventral thalamus sends fibers to the hypothalamus, pallida and prerubral nucleus. Reticular nucleus is the last link in the non-specific path to the cortex for EEG rhythms related to general consciousness. The non-specific neural system is distinct from specific sensory and other neural systems that activate the cortex. In the cortex the non-specific fibers from the reticular nucleus contact pyramidal and granule cells whose actions produce the non-specific EEG rhythms.

A Dermoid Tumor of the Lateral Ventricle Associated with Internal Hydrocephalus

Epidermoid and dermoid tumors involving the skull and intracranlal spaces are relatively rare, constituting 0.3 to 6 per cent of all cerebral tumors in various reported series. These tumors often occur beneath the pons and midbrain and extend up to the cerebel]opontile angle, causing an internal hydrocephalus, but may be found anywhere on the base of the brain from the anterior perforated substance to the foramen magnum. They may involve the cerebral hemispheres or lie within the ventricles, although reports of the latter have been meager. They appear to arise from embryonic rests, resulting from inclusions of surface ectoderm within the central nervous system during embryological development. The epidermoid variety arise from the outer ectodermal layer, producing the so-called pearly tumors, while the dermolds have, in addition, mesodermal corium with its connective tissue, fat cells, sebaceous glands, and hair follicles. The presence of hair in the tumor may be considered as pathognomonic of a dermoid or teratoid type of growth. Various reports of these tumors with detailed descriptions of their etiology, location, symptoms, appearance, pathology, and treatment have appeared in past years.~.~, 3,4 I t is not within the scope of this paper to repeat these details, but to report a dermoid tumor producing an unusual picture which we had not previously encountered or noted in earlier reports.

THE NATURAL HISTORY OF HUMAN POLIOMYELITIS

1. Studies on a large number of tissues obtained from fatal cases of human poliomyelitis have revealed that the virus is distributed predominantly in two systems: (a) certain regions of the nervous system, and (b) the alimentary tract. 2. Poliomyelitis virus was demonstrated in the walls of the pharynx, ileum, and only once in those of the descending colon, while the contents of the descending colon regularly contained the virus. 3. The presence of virus in the walls of the alimentary tract appears to be the result neither of generalized dissemination of the virus nor of secondary centrifugal spread, but rather that of primary localization or portal of entry. 4. In the absence of evidence of any demonstrable centrifugal spread to peripheral collections of nerve cells (e.g., in the superior cervical sympathetic ganglia, suprarenals, salivary glands), the presence of virus in the abdominal sympathetic plexus of one case may be indicative of at least one pathway of centripetal virus progression. 5. The absence of demonstrable virus in the nasal mucosa, olfactory bulbs, and anterior perforated substance suggests that neither the upper respiratory tract nor the olfactory pathway were affected in the cases of human poliomyelitis studied in the present investigation.