Ventral Sulcus Research Articles

Pial Relations with Spinal Cord Veins Explain MRI Occult Spinal AV Shunts

The anatomic findings (figures ​(figures11-​-6)6) demonstrate the different relations between the ventral spinal cord veins and the pial network with the leptomeninges of the cord. The ventral veins are subpial buried in the depths of the ventral fissure; the pial network is located in the subarachnoid space. Figure 1 Thoracic spinal cord ventral view. 1) anterior funiculus; 2) anterior root of the Th 10 spinal nerve; 3) radiculo medullary artery; 4) anterior spinal artery. The subjacent veins are also covered by the linea splendens (arrowheads). Figure 2 Thoracic spinal cord posterior view. The funiculi (3) as well as the veins (2) and the posterior root of the spinal nerves (1) are seen through the arachnoid tissue partially densified (arrowheads). Figure 3 Horizontal section of thoracic spinal cord (luxol fast blue). 1) Linea splendens; 2) Anterior spinal artery and its branches; 3) Ventral spinal cord venous tronc; 4) Anterior medial fissure; 5) Anterior funiculus; 6) Anterior horn; 7) Spinal cord commissure (bar = 300 micrometres). Figure 4 Horizontal section of the spinal cord at cervical level (luxol fast blue). 1) Linea splendens; 2) Unfused anterior spinal artery; 3) Anterior spinal vein covered by fasciculated pia matter. At the level of the ventral medial fissure (5) the technical staining and preparation has separated the pia glia (arrowhead). In its most anterior portion (6), the pia mater remains compact (asterisk) (bar = 200 micrometres). Figure 5 Horizontal section of the cord at cervical level (luxol fast blue). 1) Pial arterial vessels; 2) Posterior root of the spinal nerve; 3) Posterior venous trunk, superficial to the pia mater (arrowheads); 4) Lateral funiculus; 5) Posterior horn; 6) Posterior funiculus; 7) Posterior longitudinal fasciculus (bar = 200 micrometres). Figure 6 Horizontal section of the cord at the cervical segment. The arterioles (1) and the posterior spinal vein (2) run in the subarachnoid space (3). The arachnoid (arrows) and pia mater (arrowheads) are clearly demonstrated. (4) Medial posterior septum (5) posterior funiculus (bar = 200 micrometres). The visibility of the spinal veins therefore depends on the group of veins recruited to drain an arteriovenous shunt. The few cases reported with “occult” MRI examinations and AV shunts secondarily demonstrated by angiography (figures ​(figures77 and ​and8)8) illustrate this difference. Figure 7 Dural AV shunt of the tentorium draining into the spinal cord veins (A and B). The MRI fails to demonstrate perivascular veins (C and D); note the dominant drainage into the ventral spinal cord vein. Figure 8 Spinal cord AV shunt draining into ventral spinal cord vein (A). The MRI fails to demonstrate perivascular veins (B) but shows significant spinal cord ischemia (C). Slow flow lesions draining predominantly into the ventral vein of the cord may be unseen on MRI (figure ​(figure88). The ventral vein being in the depths of the ventral sulcus cannot be seen with myelographic type of sequences. On the contary, any lesion draining predominantly into the pial network and particularly the posterior group, are expected to be demonstrated on myelographic sequences. Normally enlarged pial veins are in fact subarachnoid and can therefore be seen without pathological significance. This disposition suggests that the ischemic consequences related to ventral vein congestion in comparison to the subarachnoid congestion may very well differ. The observed absence of haemorrhage in spinal dural arteriovenous shunt may be related to this anatomic distinction In addition, the absence of subarachnoid haemorrhagic episodes in most spinal AV shunts expresses an unknown property of these veins. It seems that there is no haemorrhagic venous infarction as a consequence of subarachnoid venous congestion. Instead, the subpial congestion resulting from ventral spinal cord vein involvement can lead to manifestations similar to those observed with dural or intracranial pial lesions. The linea splendens may represent ventrally a protective barrier to the congestion provoked by a spinal dural shunt and involve only the subarachnoid network. Further observations both anatomic and hemodynamic are needed to fully understand the physiopathology of spinal AV shunts and their clinical expressions. Ignorance of the venous patterns and absence of venous analysis of spinal cord angiograms still limit discussions on spinal cord ischemia to the arterial causes.

Microbilobata, a new genus of earliest terebratulid brachiopod from the lower Silurian of Northwestern Canada: Implications for the origin of higher taxa

Microbilobata avalanchensis n. gen. and n. sp. from the Lower Silurian (upper Wenlock) carbonate rocks of the lower Delorme Group in the Avalanche Lake area, northwestern Canada, is described here as the earliest known terebratulid brachiopod. These small shells (less than 2 mm long) are subtriangular, anteriorly emarginate, possibly punctate, with both valves being sulcate at their anterior halves, the ventral sulcus bearing one prominent plica, and the dorsal sulcus marked by two plicae. Internally, M. avalanchensis has a centronelliform loop extending for about three fifths of the total shell length. The shells are silicified in carbonate rocks of mid to outer shelf origin. M. avalanchensis is relatively rare, with about 40 specimens so far found from samples collected at 58–60 m above the base of section AV5 in the Avalanche Lake area. Its presence in rocks of Wenlock age extends the earliest known terebratulids back about 16 million years from the oldest previously recorded terebratulids (earliest De...

Distribution of intraventricularly injected horseradish peroxidase in cerebrospinal fluid compartments of the rat spinal cord.

The circulation of the cerebrospinal fluid along the central canal and its access to the parenchyma of the spinal cord of the rat have been analyzed by injection of horseradish peroxidase (HRP) into the lateral ventricle. Peroxidase was found throughout the central canal 13 min after injection, suggesting a rapid circulation of cerebrospinal fluid along the central canal of the rat spinal cord. It was cleared from the central canal within 2 h, in contrast with the situation in the brain tissue, where it remained in the periventricular areas for 4 h. In the central canal, HRP bound to Reissner's fiber and the luminal surface of the ependymal cells; it penetrated through the intercellular space of the ependymal lining, reached the subependymal neuropil, the basement membrane of local capillaries, and appeared in the lumen of endothelial pinocytotic vesicles. Furthermore, it accumulated in the labyrinths of the basement membrane contacting the basolateral aspect of the ependymal cells. In ependymocytes, HRP was found in single pinocytotic vesicles. The blood vessels supplying the spinal cord were classified into two types. Type-A vessels penetrated the spinal cord laterally and dorsally and displayed the tracer along their external wall as far as the gray matter. Type-B vessels intruded into the spinal cord from the medial ventral sulcus and occupied the anterior commissure of the gray matter, approaching the central canal. They represented the only vessels marked by HRP along their course through the gray matter. HRP spread from the wall of type-B vessels, labeling the labyrinths, the intercellular space of the ependymal lining, and the lumen of the central canal. This suggests a communication between the central canal and the outer cerebrospinal fluid space, at the level of the medial ventral sulcus, via the intercellular spaces, the perivascular basement membrane and its labyrinthine extensions.

The distribution of mesenchyme proteoglycan (PG-M) during wing bud outgrowth

This study utilizes immunofluorescence to describe the distribution of several extracellular matrix molecules in the chick embryo during the process of limb outgrowth and the formation of precartilage condensations. A large chondroitin sulfate proteoglycan (PG-M) is detected at the wing level at Hamburger and Hamilton stage 14 in and under the dorsal ectoderm, and is associated with the basement membranes around the neural tube, notochord and pronephros, but not with other basement membranes. The galactose-specific lectin, peanut agglutinin (PNA), has a similar distribution except that it also binds to the dorsal side of the neural tube. PG-M is not detected in the limb mesenchyme until after stage 17, when it is present in the distal region, as is PNA-binding material. With further development of the wing bud, PG-M is present in the subectodermal mesenchyme, the mesenchyme at the distal tip and in the prechondrogenic core. After stage 22 PNA-binding material becomes localized in the prechondrogenic core, the basement membranes under the apical ectodermal ridge, and the ventral sulcus. The distribution of these components (PG-M and PNA binding material) overlaps, but differs from that of type I collagen and fibronectin and basement membrane components, such as laminin, basement membrane heparan sulfate proteoglycan, and type IV collagen. Tenascin, on the other hand, is not detected in the limb bud until stage 25, after the appearance of cartilage matrix components such as type II collagen and cartilage proteoglycan (PG-H). These results are considered in relation to the formation of precartilage aggregates, and indicate that PNA binds to components in precartilage aggregates other than PG-M or tenascin.

Early development of the cerebral vesicles in man

Two human embryos which were immediately before and soon after the appearance of the cerebral vesicle were cut into complete serial sections in almost the same direction and studied comparatively. The findings on these two sets of serial sections indicate that the rostral continuations of subthalamus and ventral thalamus along the ventral thalamic sulcus continuing from the sulcus limitans of the midbrain are destined to give rise to the formation of the cerebral vesicle. The rostral continuation of the subthalamus becomes the floor of the interventricular foramen, and that of the ventral thalamus the pallium. The rostral end of the continuation of the subthalamic matrix is not only the site of the beginning of evagination of the cerebral vesicle, but also the site of elevation of the ganglionic hill or striatum. As the evagination of the cerebral vesicle proceeds exceedingly dorsocaudolaterally from the rostral end of the continuation of the ventral thalamus, the elevation of the striatum occurs also in the same direction, getting in touch with the folding of the hemispheric stalk of Kuhlenbeck to enclose the interventricular foramen. Tt is noticed that, at the beginning of evagination, the grade of depression of the nasal pit was always parallel with that of evagniation of the cerebral vesicle.

Functional micromorphology and circadian growth of the rock-boring clam Penitella penita

Ground sections, acetate peels, and scanning electron microscopy are used to visualize the microstructure and fine growth lines of the shells of Penitella penita, collected from different substrates. Growth increments of approximately daily duration were found in the area of the umbonal ventral sulcus. Two morphologically different types of growth increments are described, those deposited during the period of quiescence and growth (7 to 10 days) and those deposited during the succeeding period of active boring (5 to 8 days). The duration of a full cycle of growth and boring varies considerably, but averages 15 days.The width of growth increments and the microstructure of the shell is controlled by the amount of space within the burrow, and this in turn depends primarily on the substrate hardness. The effect of other factors, such as disturbance, and tidal and seasonal fluctuations, is minor by comparison.The microstructure of juveniles differs from that of older animals and the number of lines per group is reduced.

39. The Comparative Anatomy of the Tongues of the Mammalia. – VI. Summary and Classification of the Tongues of the Primates.

39. The Comparative Anatomy of the Tongues of the Mammalia. – VI. Summary and Classification of the Tongues of the Primates.

VI.—Brachiopod Morphology: Notes and Comments on Dr. J. Allan Thomson's Papers

From a long and careful study of the Brachiopoda I am led to offer some observations upon the two recently published papers by Dr. J. Allan Thomson which have appeared in this Magazine. In the case of Dallina I cannot agree with Dr. Thomson regarding the type of folding. He considers D. septigera (the genotype) and D. raphaelis as dorsally biplicate, D. floridana as dorsally uniplicate. Now dorsal biplication is brought about by the dorsal sulcus being superimposed upon a single dorsal fold. In D. septigera, as well as in D. floridana, a broad ventral sulcus is superimposed upon a dominant ventral fold; these two species, therefore, are, in my opinion, ventrally biplicate (as in Magellania flavescens and some others).