Foramen Of Magendie Research Articles

The apertural system of pollen grains in Anthemideae and Cardueae (Compositae) with special reference to the mesoaperture

The apertural system of most Compositae pollen grains is made up of an ectoaperture and an endoaperture. Light microscopic observations reveal a median aperture or “mesoaperture” in some Compositae, however, there is certain controversy as to which layers are involved. LM, SEM and TEM observations of preparations from the tribes Anthemideae and Cardueae show that the ectexine and the endexine become thin or discontinuous at the ectoaperture and endoaperture, respectively, However, only in Cardueae is there a distinct mesoaperture involving the foot layer and the outer layer of the endexine. It seems that in Anthemideae this median aperture is a series of rims around the endoaperture and/or folds of the endexine. Given the difficulties in these observations and the possibility of error, it is suggested that the term “mesoaperture” be used only in a relative sense, indicating a median situation between the ecto- and endoapertures and when the layers involved are known.

Pathological findings in suboccipital decompression in 63 patients with syringomyelia.

Out of 97 patients with syringomyelia treated surgically, in 63 of them suboccipital decompression was performed. Various kinds of congenital or early acquired abnormalities were found to be the possible cause of the disease. Simple Arnold-Chiari malformation was found in 29 patients. In next 16 cases the Arnold-Chiari malformation was accompanied by partial occlusion of the foramen of Magendie with tiny, translucid membrane, that covered lower 1/2 or 3/4 of the foramen. In another 9 cases of Arnold-Chiari malformation, foramen of Magendie was totally occluded with thick, grayish membrane. In 7 cases lowered cerebellar tonsils were firmly attached to the medulla and joined by adhesions between themselves. In 1 case total atresia of foramen of Magendie was present only. In 1 case no pathological changes were found. The above mentioned findings point out, that in practically all the cases of syringomyelia various kinds of gross pathology, that leads to difficulties in normal outflow of the CSF from the IVth ventricle to cisterns can be found. From that point of view the suboccipital decompression seems to be the most reasonable surgical procedure.

Ultrastructural observations of the development of the fourth ventricular roof in the mouse brain

The developmental changes of the fourth ventricular roof of the brain in mouse fetuses and neonates were observed by scanning and transmission electron microscopy with particular attention to the caudal portion where a median foramen might be formed during the fetal period. The fourth ventricular roof was continuously paved with a single layer of cuboidal or squamous neuroepithelial cells with poorly developed basement membrane until the 12th intrauterine day when the primitive choroid plexus appeared at the middle portion of the roof. With development of the choroid plexus, the roof caudal to the choroid plexus (membranous roof) became thinner, and it was mostly lined with a single layer of flat ependymal cells having cilia and microvilli and resting on a continuous basement membrane. These ependymal cells were connected with one another by a gap junction or an intermediate junction for the entire period examined, except at the 13th to 14th intrauterine days, during which the interependymal clefts were transiently widened up to 2 microns in width, in places, without disruption of the continuous basement membrane. Neither a median aperture nor wide intercellular pores were formed in the membranous roof during the fetal or neonatal term.

The MR appearance of CSF flow in patients with ventriculomegaly.

The purpose of this study was to investigate the MR imaging appearance of mobile CSF in the ventricular system in patients with ventriculomegaly caused by brain atrophy and extraventricular obstructive hydrocephalus. Pulsatile CSF often has decreased intensity relative to less mobile areas of CSF, particularly on T2-weighted scans. At times, the flow-related signal dropout causes striking heterogeneity in the appearance of CSF. This has been termed the CSF flow-void sign (CFVS) and is most likely caused by spin-phase shifts and time-of-flight effects created as a result of CSF turbulence and increased velocity of CSF pulsatile flow. The effect is most pronounced in areas where a larger volume of CSF moves through a small channel or foramen, such as the aqueduct of Sylvius or foramen of Magendie. The scans of 40 patients with ventriculomegaly caused by brain atrophy or extraventricular obstructive hydrocephalus were reviewed for the presence of the CFVS. All patients had the CFVS in the aqueduct of Sylvius on T2-weighted spin-echo sequences. The sign was present in the fourth ventricle in 96%, in the third ventricle in 70%, in the foramen of Magendie in 65-77%, and in the foramina of Monro in 33%. The sign was more pronounced in patients with larger ventricles but could not be used to differentiate patients with brain atrophy from those with extraventricular obstructive hydrocephalus.

Hydrocephalus due to Membranous Obstruction of Magendie's Foramen

The authors report a rare case of membranous obstruction of Magendie's foramen with internal hydrocephalus. A 30-year-old male was referred from another hospital because of dilatation of the entire ventricular system, as evidenced by computed tomography (CT). The patient had suffered headache, dizziness, nausea, and vomiting for several years. On admission, bilateral papilledema was prominent. A ventriculoperitoneal shunt was emplaced on the next day. Postoperative CT showed that the lateral and third ventricles had decreased in size, while the fourth ventricle was still enlarged. The patient rejected further surgery and was discharged. Three months later the symptoms reappeared. The patient underwent a suboccipital craniectomy, which revealed a semi-translucent membrane obstructing Magendie's foramen. The membrane was resected, and histopathological examination disclosed that it was composed of loose connective tissue, which was partially cellular and contained hemosiderin deposits, covered by a layer of flattened cells. After surgery, all symptoms disappeared and the patient was discharged. At 6 months after discharge, the fourth ventricle had decreased in size.

Radiographic studies of the ventricles in syringomyelia.

Radiographic investigations of 171 patients with "communicating' syringomyelia have been reviewed. Hydrocephalus was found in one-third of the cases and has occasionally progressed after operation on the posterior fossa, sometimes with accompanying clinical deterioration. The outlets of the fourth ventricle were usually abnormal; tonsillar descent, arachnoiditis and both together were seen. Arachnoiditis correlated strongly with a history of difficult birth. The foramen of Magendie was sometimes patent and sometimes blocked. There was no consistent level of occlusion corresponding to a persistent roof of the fourth ventricle. The cisterna magna was usually small or obliterated but some examples of large cisterns or subarachnoid pouches were found. Radiological demonstration of a communication from the fourth ventricle to the syrinx occurred in only seven patients by positive contrast material and not by air. It is suggested that a sizable communication is rare at the time when patients seek treatment.

FATAL BCG INFECTION IN AN IMMUNOCOMPETENT GIRL

A 6-year-old girl developed progressive symptoms of increased intracranial pressure starting 5 months after BCG vaccination. Thirteen months later craniotomy revealed an epithelioid cell granuloma of the arachnoid occluding the foramen of Magendie. No tubercle bacilli were found on histological examination. Insertion of a Pudenz shunt relieved the symptoms. Six months later generalized BCG infection developed, and in spite of treatment with ethambutol, rifampicin and isoniazid for 10 weeks, death occurred during an episode of increased intracranial pressure. Mycobacterium BCG could be cultured from several organs. The patient showed no obvious evidence of immuno-deficiency as judged on the basis of previous disease history, particle concentration of granulocytes, B and T lymphocytes in peripheral blood, concentration of immunoglobulins in serum, response of lymphocytes to transformation with mitogens and antigens, and histological findings in the thymus and BCG granulomas.

THE SIGNIFICANCE OF NON-FILLING OF THE VENTRICULAR SYSTEM AT PNEUMOENCEPHALOGRAPHY

The present series has the lowest incidence reported of unexplained ventricular non-filling at PEG.A number of appropriate technical maneuvers have been utilized to enhance ventricular filling and reduce the number of non-filling cases.Some abnormality in the cisterna magna, vallecular fossa or foramen of Magendie, probably anatomic, is believed to be responsible for the failure in filling of the cerebral ventricles in the presence of otherwise normally patent subarachnoid spaces.In addition, there is no evidence from this series to suggest any cause and effect relationship between ventricular non-filling and the presence of tumor, in the absence of compression or distortion of the subarachnoid spaces. Likewise, subdural air injection has not been found to be of significance in the probability of tumor.

Hydrocephalus due to membranous obstruction of the fourth ventricle.

✓ Four patients with hydrocephalus due to membranous obstruction of the fourth ventricle are presented. This rare entity produced radiographic and clinical findings suggestive of posterior fossa tumor. Operative findings included normal cerebellar development and a translucent membrane just above the foramen of Magendie. Etiological possibilities are discussed.

Extension of posterior fossa tumors, particularly intraventricular fourth ventricle tumors, into the upper cervical spinal canal.

EXTENSION OF POSTERIOR FOSSA TUMORS, PARTICULARLY INTRAVENTRICULAR FOURTH VENTRICLE TUMORS, INTO THE UPPER CERVICAL SPINAL CANALBERNARD S. EPSTEIN, M.D., JOSEPH A. EPSTEIN, M.D. and ROBERT CARRAS, M.D.Audio Available | Share

The technique and preliminary results of intraventricular EEG recording (brain-stem EEG)

The method of intraventricular EEG recording as developed by the author is presented: suboccipital puncture is made with a special needle which consists of two barrels, one inside the other, each of which has a longitudinal slit on opposite sides. After the bundle of electrodes, which is composed of 2–8 insulated silver wires (diameter of each wire 0.065–0.12 mm) is inserted, it glides forward along the dorsal plane of the medulla and, by its medial position, reaches the ventricular system through the foramen of Magendi. Out of a total of 22 punctures the ratio of successful to unsuccessful attainment of the ventricular system was 1:3. The same insertion of the electrodes was performed on four dogs. Histopathological examinations showed neither damage nor later reactions of the brain tissue. A case of Jacksonian epilepsy is presented in which, during an attack, theta activity could be recorded in the brain-stem area. The hope is expressed that the method here presented will permit new insight into the electrical activity of the brain-stem area.

An operative staging system and a megavoltage radiotherapeutic technic for cerebellar medulloblastomas.

CEREBELLAR MEDULLOBLASTOMA is one of the most common types of primary intracranial tumors in children. The treatment of this tumor, unfortunately, is considered as “one of the darkest chapters in pediatric neurosurgery” (1). Cushing (2) reported an average survival of five and six-tenths months in 14 patients with medulloblastoma who received no postoperative radiotherapy. Ingraham and Matson (3) stated that “to our knowledge, no patient with cerebellar medulloblastoma has ever been cured.” Although medulloblastoma has long been known as the most sensitive primary brain tumor to ionizing radiation, the radiotherapy results for this tumor with respect to long-term survival is still very disappointing. In order to better evaluate the response of medulloblastoma to irradiation and to improve the survival rate, the operative records of 100 consecutive cases of tissue-proved medulloblastoma at the Neurological Institute, Columbia-Presbyterian Medical Center were arbitrarily taken in a period from 1940 to 1967 and were reviewed as to their primary location, extent of invasion, and gross subarachnoid seeding in correlation with radiation dose, technic, and survival results when possible. The age and sex distribution in this series is shown in TABLE I. Since clinical staging is inaccurate and sometimes misleading in many inaccessible human cancers, we have sought to develop an operative staging system for medulloblastomas with the International TNM-staging designation. The letter T stands for the primary tumor, subdivided to T1, T2, T3, T4, according to its size and the extent of involvement. Since there are no lymphatic channels in the brain, the letter N is omitted in our staging. The letter M stands for metastasis. In the cases of medulloblastoma, the cerebrospinal fluid pathway is the most important route of metastasis. The extent of metastasis is subdivided to Mo, Ml, M2, M3. Our proposed operative staging system for cerebellar medulloblastoma is as follows (Fig. 1): T1—Tumor less than 3 em in diameter and limited to the classic midline position in the vermis, the roof of the fourth ventricle, and less frequently to the cerebellar hemispheres. T2—Tumor more than 3 em in diameter, further invading one adjacent structure or partially filling the fourth ventricle. T3—It may be subdivided into T3a and T3b. T3a: Tumor further invading two adjacent structures or completely filling the fourth ventricle with extension into the aqueduct of Sylvius, foramen of Magendie, or foramen of Luschka, thus producing marked internal hydrocephalus. T3b: Tumor arising from the floor of the fourth ventricle or brain stem and filling the fourth ventricle.

Radiographic diagnosis of the Dandy-Walker syndrome with the emphasis on angiography.

In two recent cases of the Dandy-Walker syndrome we have noted two abnormalities which we believe have not been previously emphasized in the American literature. These are elongation of the vein of Galen and a high position of the straight sinus. The Dandy-Walker syndrome is a cerebellar anomaly in which a cystic balloon-like dilatation of the fourth ventricle is associated with hydrocephalic dilatation of the lateral and third ventricles (1, 3, 5, 9). The foramina of Magendie and Luschka may be occluded or individually patent (6). The anterior part of the vermis is displaced upward but is otherwise normal. The posterior vermis is underdeveloped and it is continuous caudally with a membrane consisting internally of ependyma and externally of connective tissue. This membrane is usually adherent to the pia arachnoid of the posterior fossa and represents the roof of the greatly distended fourth ventricle (1). It replaces the normal posterior medullary velum. The large posterior fossa contents prevent the tentorium from making its normal descent during fetal life. This produces a characteristic high position of the lateral sinuses (10). Neuropathologists disagree on the primary mechanism in the development of the defect. Many authors believe that the fourth ventricular foraminal atresia is primary and gives rise to a hydrocephalus which is responsible for the maldevelopment of the vermis (5, 10). Others believe that the basic abnormality is a meningocele of the posterior medullary velum and that the fourth ventricular foramina, though usually occluded, are not the causes of the anomaly (1). Neither argument is conclusive, but the radiologist should know that occasionally one or all of the foramina are patent (1, 5), allowing the entrance of air during lumbar pneumoencephalography and the exit of air or Pantopaque during air-Pantopaque ventriculography. Case I: A ten-week-old Caucasian female entered the hospital on Jan. 27, 1966, because her pediatrician had noted an abnormally rapid head enlargement. The head circumference was 46 cm and had increased 2.5 cm in the preceding two weeks. The anterior fontanelle was tense and bulging. The optic disks were slightly swollen. The remainder of the neurological and general examination was normal. The child ate well and appeared happy. Right retrograde brachial arteriograms and air-Pantopaque ventriculograms were considered diagnostic of the Dandy-Walker syndrome (Figs. 2–4). On Feb. 1 the neurosurgeon performed a posterior fossa exploration. A large, cyst-like fourth ventricle containing fluid was found, entered, and its wall partly excised, leaving it communicating with the subarachnoid space of the spinal canal. The cerebellar hemispheres were rudimentary. A ventriculoatrial shunt was performed. The child returned home on Feb. 14 with a functioning shunt and a soft fontanelle.

Tuberculous meningitis. The clinical pattern of sterile meningitis, pneumonia, and hydrocephalus or split sutures. A study of 14 patients seen between 1956 and 1967.

BECAUSE meningitis is the primary cause of death from tuberculosis in children (2), diagnosis is urgent. If only the parameters of tuberculin skin test, contact history, and organism identification are used, antituberculous therapy may often be withheld. Associated pneumonia, split sutures, hydrocephalus, and cerebral arterial changes also indicate tuberculous origin of sterile meningitis. Pneumonia without calcification has been reported in 43 to 75 per cent (2, 10) of children with tuberculous meningitis. This is not necessarily characteristic in pattern. Adenopathy, calcification, miliary disease, or pleural effusion has been present in fewer patients. These findings are especially significant when meningitis is the presenting manifestation of tuberculosis. Acheson and Smith (1) and Foltz and Sheehy (5) have noted that major degrees of hydrocephalus are characteristic of the more severe cases, and that it carries a poor prognosis. In tuberculous meningitis studied by pneumoencephalography, hydrocephalus has been reported in 40 to 68 per cent (13, 5) of pediatric patients. The hydrocephalus is usually communicating, with the block at the sylvian and interpeduncular cisterns, but obstruction has also been described at the aqueduct (8), at the foramen of Magendie and Luschka (13), and at two levels (5). Spasm or narrowing about the internal carotid artery bifurcation has been described by Greitz (6) and Lehrer (8). Intracranial calcification has not been found until fifteen months after the onset of meningitis (11). Patients with Tuberculous Meningitis The 14 patients of this report were hospitalized at St. Louis Children's Hospital or Barnes Hospital between 1956 and 1967. Six were Negro, 8 Caucasian, 5 female, and 9 male. Five were between eleven months and twenty-four months of age, 6 were between four and seven years of age, and 3 adults were twenty-one, thirty-three, and sixtv-six years old. Chest radiographs were obtained on 13 patients. Pneumonia was present in 9, and in 4 of these there was also hilar adenopathy and in another apical pleural thickening. In 1 patient only hilar adenopathy was noted radiographically, although pneumonia was present at autopsy (Fig. 1). A calcified 5 mm parenchymal nodule was observed in another infant, whose hilar lymph nodes later became enlarged and calcified during antituberculous therapy. The only 2 chest examinations failing to indicate possible active pulmonary disease were in adults. Skull examination disclosed split sutures in 6 patients: aged eleven months, one, one, two, four, and seven years. The sutures were closed in 7 patients aged four, five, six, seven, twenty-one, thirty-three, and sixty-six years. In 3 patients with closed sutures air studies showed dilated ventricles. The hydrocephalus was of the communicating type in 2 cases (Fig. 2), with air reaching the sulci in a third.

CYSTIC PROLONGATION OF FOURTH VENTRICLE. AN ANOMALY ASSOCIATED WITH THE ARNOLD-CHIARI MALFORMATION.

In cases of the Arnold-Chiari malformation, the foramen of Magendie has been variously reported as being present or absent. All authors agree, however, that the caudal extremity of the cerebellar component of the malformation is bound down by dense fibrous adhesions in which the choroid plexus of the fourth ventricle is included. 1 Since the choroid plexus normally passes through the foramen of Magendie, it is apparent that in the presence of such adhesions considerable difficulty in identification of the foramen may be encountered. Alvord 2 summarizes the position in the following words: The foramen of Magendie is elongated, and frequently extends well below the level of the foramen magnum; it may be patent, or it may be occluded by fibrous adhesions between the cerebellum and medulla at or below the foramen magnum. Within these fibrous adhesions choroid plexus is found. Some authors have described other conditions of the foramen

Atresia of the foramina of Luschka and Magendie; a cause of obstructive internal hydrocephalus.

The commonest causes of noncommunicating hydrocephalus in infancy are developmental obstructions at the aqueduct of Sylvius or in the region of the foramina of Luschka and Magendie. Malformation of the aqueduct is most frequently observed, but atresia of the foramina of Luschka and Magendie or functional blockage secondary to an Arnold-Chiari malformation are not uncommon. Embryologically, the foramen of Magendie is usually formed by the fourth month of fetal life. At this stage of development the cerebellum is dumbbell-shaped with an underdeveloped vermis in the midline connecting two primitive cerebellar hemispheres. Since fluid has already started to form within the cerebral vesicles, the failure of normal formation of the posterior foramina leads to fluid accumulation in the fourth ventricle, inhibiting further development of the cerebellum. As the posterior fossa is thus enlarged because of the cystic dilatation of the fourth ventricle, the developing occipital lobes of the cerebrum cannot push

Calcified Ependymoblastoma of the Fourth Ventricle in a Four-Year-Old Girl: Roentgen Demonstration

Calcification is rare in the gliomas found in children under four years of age. Rarer still is the demonstration of calcium by roentgenography; this is especially true when the calcified lesion lies in the posterior fossa. Because it possesses these unusual features, this single instance is presented as a case study. J. D., a white female, 3 years and 7 months of age, was first admitted to the Neurosurgical Service at the University of California Hospital on Sept. 6, 1939. Beginning two and a half months before entry, without previous relevant illness, she had had periodic nausea, vomiting, and anorexia. At first the presence of a tumor of the posterior fossa was not recognized. When the child was seen on Jan. 6, 1940, spasticity, ataxia, cracked-pot percussion note, and bilateral papilledema were present. Roentgenograms of the skull on Jan. 8, 1940 (Figs. 1 and 2) showed a calcified midline lesion in the posterior fossa. For some time, children admitted to this hospital with findings suggestive of tumor of the posterior fossa have been given a course of roentgen therapy as a therapeutic test for a radiosensitive neoplasm. It was felt that this therapy should be administered first even in a situation such as will be described, in which the lesion was known to contain radiopaque material, probably calcium. Accordingly the child received 1900 r through each of two ports in the lateral occipital region. Temporary improvement followed, despite an intercurrent mastoiditis. By September 1940, however, it was obvious that a craniotomy would be necessary. A firm grayish red growth was removed from the fourth ventricle. This tumor extended from the aqueduct of Sylvius, through the fourth ventricle and foramen of Magendie, to the level of the lamina of the second cervical vertebra. Its only attachment was in the midline near the calamus scriptorius. In separating this attachment it was necessary to clip one large vessel. This initiated retrograde thrombosis, which resulted in extensive medullary necrosis and death on the second day. Histopathologically, the tumor was a calcified ependymoblastoma with extensive degeneration. The cells were uniform with regular oval-round nuclei and long coarse processes characteristically lined up and attached. The calcium was identified by means of stained preparations, including von Kossa's technic. In 100 cases of intracranial tumor in children Bailey, Buchanan, and Bucy (1) found only 7 ependymomas, 5 of which occurred in children less than four years of age. Other cases of ependymoma in this age group have been reported by Mackay (2), Gross (3), Bailey and Cushing (4), and Fincher and Coon (5); 7 of the 9 were found in males. Only one of these authors (Mackay) mentioned the demonstration of calcium by histologic study; we assume that in the other cases none was found.

Intracranial Studies by Ventriculograms

VENTRICULOGRAMS are radiographs of the ventricular system after the cerebrospinal fluid has been completely or partially replaced by air. In order to understand the abnormalities in the ventricular system it is necessary to have a minute knowledge of anatomy and physiology. To review these briefly, let us recall that the intracranial ventricular system is composed of two lateral ventricles, a third ventricle, and a fourth ventricle. One lateral ventricle lies in each hemisphere of the brain and is composed of anterior, posterior, and temporal horns. The anterior horns are somewhat larger and more rounded, while the posterior horns come more to a point and are separated much farther apart than the anterior horns. The temporal horns are the smaller and extend downward and forward. These horns form more or less a wishbone-shape, as is seen in the lateral view. The capacity of the normal ventricle is about 60 c.c. From near the center of the anterior horn on the medial side is the foramen of Monro, which connects each lateral ventricle with the third ventricle. The third ventricle is slightly oblong in shape, is situated just below and between the two lateral ventricles, and is seen between the anterior and temporal horns on the lateral view. From the posterior portion of the floor of the third ventricle there is seen a funnel-shaped opening, leading downward and backward into a comparatively narrow channel, the aqueduct of Sylvius, which connects with the fourth ventricle. As is seen laterally, the fourth ventricle is a small triangular shaped cavity located in the posterior fossa. From this triangular shaped cavity, at the upper and posterior portion of the triangle, is seen the foramen of Magendie, and at the lower and most dependent angle are seen the foramina of Luschka. These three foramina connect the ventricular system with the subarachnoid space. The cerebrospinal fluid enters the lateral ventricles through the choroid plexuses, one of which lies on the floor of each anterior horn, and passes through the foramen of Monro into the third ventricle, and from the third ventricle through the aqueduct of Sylvius into the fourth ventricle; then through the foramina of Luschka and Magendie to the subarachnoid space, where it is taken up by the blood stream. This anatomy is illustrated by Figures 1 and 2. This illustration is made by taking a brain after autopsy and, before hardening or shrinking, injecting the ventricular system with neosilvol and radiographing from above downward and laterally. Indications for ventricular study are: persistent headaches that cannot be accounted for otherwise, tumors, abscesses, edema, hydrocephalus, epilepsy other than congenital types, congenital deformity. The value of the study depends, first, on the safety of the procedure; second, on the reliability of the technic, and third, on the interpretation of the findings.

THE EARLY RECOGNITION OF HYDROCEPHALUS IN MENINGITIS

Interference with absorption of the cerebrospinal fluid in acute meningitis may be brought about by an exudate so localized that it obstructs the foramen of Magendie and the foramina of Luschka, or the exudate may block, partially or completely, the cisternae (magna, interpeduncularis and pontis) at the base of the brain and so prevent the free distribution of cerebrospinal fluid throughout the cerebral subarachnoid space. The spinal subarachnoid space may be filled partially or completely with exudate, thus limiting the participation of this surface in the absorption of the cerebrospinal fluid. Various combinations of these processes may coexist. In any event, if the absorption of cerebrospinal fluid is diminished for a sufficient length of time, hydrocephalus is produced. A brief discussion of the formation and the circulation of the cerebrospinal fluid and the more recent information concerning hydrocephalus will not be out of place here. Cerebrospinal fluid is formed within

EXPERIMENTAL HYDROCEPHALUS

Internal hydrocephalus can be produced experimentally by injecting a foreign substance into the ventricles. In these experiments, aleuronat, a granular, insoluble material, has caused an acute inflammatory reaction, characterized in the first week by an exudate consisting largely of polynuclear leucocytes. Later the picture is one of a chronic process; polynuclear cells are replaced by lymphoid and large mononuclear cells and there is proliferation of the connective tissue in the choroid plexus. Proliferation of the ependyma occurs in the first week but becomes more advanced in the second and third weeks, and there is increase in neuroglia more marked in the long continued experiments. Ordinarily when aleuronat is injected into a serous cavity, the pleural cavity, for example, abundant accumulation of fluid takes place in twenty-four to forty-eight hours, and at the same time polynuclear leucocytes collect. In the experiments in which the irritant was injected into the ventricle of the brain there was little or no dilatation apparent in the first week; absence of dilatation in all probability is due to the free outflow of the fluid. When obstruction occurs during the chronic stage of the inflammatory process dilatation of the ventricle follows. Choked disc and other symptoms of increased intracranial pressure accompany experimental hydrocephalus. Dilatation occurs slowly and reaches a maximum in about two months. In some of the experiments of longer duration obstruction can be demonstrated in gross or microscopically. Obvious obstruction has not been found by gross examination in all instances, but in the experiments in which India ink was injected into the ventricle before death obstruction to outflow was very readily demonstrated. The third and fourth ventricles were in all instances filled with the pigment, but none appeared on the surface of the brain, whereas in normal dogs the entire surface, especially the base, became deeply pigmented. Obstruction to the circulation of cerebrospinal fluid causing internal hydrocephalus may occur at the foramen of Monro, in the aqueduct of Sylvius, or, doubtless with greatest frequency, at the foramen of Magendie.