Leonardo's achievements are universally recognized, as artist, anatomist and much more beside... more Leonardo's achievements are universally recognized, as artist, anatomist and much more besides. As an anatomist, he is said to have performed and extensively observed dissections. He recorded his findings in his celebrated drawings. He made at least a dozen drawings described as being of a human fetus. About half are shown apparently realistically curled up within the uterus. In the most widely reproduced of them it is well known that the uterus is not human, but is that of an ungulate, a point confirmed by the form of the placenta. It is said that Leonardo dissected a pregnant human uterus, at 4 months of gestation. The figure in the drawing, which is sometimes said to have been made of this, cannot show a 4-month-old fetus, not least because its head is too small relative to the rest of its body. This disparity necessarily raises the question of the age and status of Leonardo's other images said to show fetuses. The reliability of these can be addressed using data on human growth both before and after birth. These data provide detailed information on the growth of a wide range of body parameters, including changes in the proportion of head height to total body height. Knowing this proportion enables the age of the fetus or infant to be estimated accurately (Fraher. Computers and the History of Art. 5, 1995). In all of Leonardo's drawings of what are generally referred to as fetuses, the head forms slightly more than one-fifth of the total length. By using this method of age estimation, it is clear that the image is not that of a fetus, but of an infant of at least 6 months. The drawings of the ‘fetus’ in utero are therefore constructed from three elements, none of which is what it purports to be. The fetus is in fact a postnatal infant, while the uterus and placenta are those of a cow or deer.
This book is everything its title suggests. Nine hundred pages, mostly by highly respected worker... more This book is everything its title suggests. Nine hundred pages, mostly by highly respected workers, covering all aspects of the modern science of molecular neurobiology from membrane channels through genetics to the molecular biology of behaviour. It is a must for anyone teaching or researching in this area. What a pity it is SO expensive!
The fifth lumbar ventral spinal nerve rootlets join to form a number of aggregated rootlet bundle... more The fifth lumbar ventral spinal nerve rootlets join to form a number of aggregated rootlet bundles. These in turn fuse to form the ventral root. Each rootlet is surrounded by a sheath which consists of a single fenestrated layer of cells and their attenuated cytoplasmic processes and which is open ended proximally. Immediately superficial to the spinal cord surface, rootlets are separated from one another by a labyrinth of inter-radicular spaces containing small blood vessels. Between adjacent rootlets the inter-radicular space tapers distally to an apex. The endoneurial space of the rootlet communicates with the subpial and inter-radicular spaces. Each aggregated rootlet bundle is surrounded by a multilayered sheath. Proximally, the outer layers of this sheath are continuous with the superficial layers of the pia mater. Both of these, as well as the root sheath with which the rootlet bundle sheaths are continuous distally, are complete and lack fenestrations. Accordingly, the endoneurial space, though continuous with the inter-radicular and subpial spaces, is isolated from the subarachnoid space.
The floor plate of the neural tube is of major importance in determining axonal behaviour, such t... more The floor plate of the neural tube is of major importance in determining axonal behaviour, such that, having crossed, decussating axons do not cross back again. The ventral commissure (VC) of the spinal cord forms immediately ventral to the floor plate shortly after neural tube closure. It is the principal location in which decussating axons cross the midline. It is probably also of major importance in neural tube development, but has received relatively little attention. This study analyses the growth and development of the rat VC and also axon-glial relationships within it throughout the crucial prenatal period of extensive transmedian axon growth, when key biochemical interactions between the two tissues are taking place. The morphometric, stereological and immunohistochemical methods used show that the axonal and glial populations remain in a finely balanced equilibrium throughout a period of almost a hundred-fold growth of both elements. At all stages axons are highly segregated into small bundles of constant size by glial processes, to which they are closely apposed. Thus, glial-axon contact is remarkably precocious, uniquely intimate and persists throughout VC development. This suggests that the relationship between the two tissues is highly controlled through interactions between them. The VC is likely to be the physical basis of a second set of glial-axonal interactions, namely, those which are well known to influence axon crossing behaviour. In mediating these, the extensive axon-glial contact is an ideal arrangement for molecular transfer between them, and is probably the substrate for altering axon responsiveness and ensuring reliable transmedian decussation. The VC is therefore a segregating matrix temporally and spatially specialised for a range of key developmental axon-glial interactions.
Leonardo's achievements are universally recognized, as artist, anatomist and much more beside... more Leonardo's achievements are universally recognized, as artist, anatomist and much more besides. As an anatomist, he is said to have performed and extensively observed dissections. He recorded his findings in his celebrated drawings. He made at least a dozen drawings described as being of a human fetus. About half are shown apparently realistically curled up within the uterus. In the most widely reproduced of them it is well known that the uterus is not human, but is that of an ungulate, a point confirmed by the form of the placenta. It is said that Leonardo dissected a pregnant human uterus, at 4 months of gestation. The figure in the drawing, which is sometimes said to have been made of this, cannot show a 4-month-old fetus, not least because its head is too small relative to the rest of its body. This disparity necessarily raises the question of the age and status of Leonardo's other images said to show fetuses. The reliability of these can be addressed using data on human growth both before and after birth. These data provide detailed information on the growth of a wide range of body parameters, including changes in the proportion of head height to total body height. Knowing this proportion enables the age of the fetus or infant to be estimated accurately (Fraher. Computers and the History of Art. 5, 1995). In all of Leonardo's drawings of what are generally referred to as fetuses, the head forms slightly more than one-fifth of the total length. By using this method of age estimation, it is clear that the image is not that of a fetus, but of an infant of at least 6 months. The drawings of the ‘fetus’ in utero are therefore constructed from three elements, none of which is what it purports to be. The fetus is in fact a postnatal infant, while the uterus and placenta are those of a cow or deer.
This book is everything its title suggests. Nine hundred pages, mostly by highly respected worker... more This book is everything its title suggests. Nine hundred pages, mostly by highly respected workers, covering all aspects of the modern science of molecular neurobiology from membrane channels through genetics to the molecular biology of behaviour. It is a must for anyone teaching or researching in this area. What a pity it is SO expensive!
The fifth lumbar ventral spinal nerve rootlets join to form a number of aggregated rootlet bundle... more The fifth lumbar ventral spinal nerve rootlets join to form a number of aggregated rootlet bundles. These in turn fuse to form the ventral root. Each rootlet is surrounded by a sheath which consists of a single fenestrated layer of cells and their attenuated cytoplasmic processes and which is open ended proximally. Immediately superficial to the spinal cord surface, rootlets are separated from one another by a labyrinth of inter-radicular spaces containing small blood vessels. Between adjacent rootlets the inter-radicular space tapers distally to an apex. The endoneurial space of the rootlet communicates with the subpial and inter-radicular spaces. Each aggregated rootlet bundle is surrounded by a multilayered sheath. Proximally, the outer layers of this sheath are continuous with the superficial layers of the pia mater. Both of these, as well as the root sheath with which the rootlet bundle sheaths are continuous distally, are complete and lack fenestrations. Accordingly, the endoneurial space, though continuous with the inter-radicular and subpial spaces, is isolated from the subarachnoid space.
The floor plate of the neural tube is of major importance in determining axonal behaviour, such t... more The floor plate of the neural tube is of major importance in determining axonal behaviour, such that, having crossed, decussating axons do not cross back again. The ventral commissure (VC) of the spinal cord forms immediately ventral to the floor plate shortly after neural tube closure. It is the principal location in which decussating axons cross the midline. It is probably also of major importance in neural tube development, but has received relatively little attention. This study analyses the growth and development of the rat VC and also axon-glial relationships within it throughout the crucial prenatal period of extensive transmedian axon growth, when key biochemical interactions between the two tissues are taking place. The morphometric, stereological and immunohistochemical methods used show that the axonal and glial populations remain in a finely balanced equilibrium throughout a period of almost a hundred-fold growth of both elements. At all stages axons are highly segregated into small bundles of constant size by glial processes, to which they are closely apposed. Thus, glial-axon contact is remarkably precocious, uniquely intimate and persists throughout VC development. This suggests that the relationship between the two tissues is highly controlled through interactions between them. The VC is likely to be the physical basis of a second set of glial-axonal interactions, namely, those which are well known to influence axon crossing behaviour. In mediating these, the extensive axon-glial contact is an ideal arrangement for molecular transfer between them, and is probably the substrate for altering axon responsiveness and ensuring reliable transmedian decussation. The VC is therefore a segregating matrix temporally and spatially specialised for a range of key developmental axon-glial interactions.
Uploads
Papers by John Fraher