. Elements of comparative anatomy. Anatomy, Comparative. I?) Spinal Chord. § 383. The spinal chord, which is continuous with the medulla oblongata, is formed from the de- velopment of the lateral halves of the wall of the primitive medullary tube. As the lateral parts in- crease in size an anterior longitudinal fissure is de- veloped. The primitive lumen of the tube is con- verted into the central canal. The central appara- tus of the spinal chord occupies the inner parts, and forms a gray medul- lary mass, which is seen, in cross section, to have the form of cornua, which pass forwards and ba
. Elements of comparative anatomy. Anatomy, Comparative. I?) Spinal Chord. § 383. The spinal chord, which is continuous with the medulla oblongata, is formed from the de- velopment of the lateral halves of the wall of the primitive medullary tube. As the lateral parts in- crease in size an anterior longitudinal fissure is de- veloped. The primitive lumen of the tube is con- verted into the central canal. The central appara- tus of the spinal chord occupies the inner parts, and forms a gray medul- lary mass, which is seen, in cross section, to have the form of cornua, which pass forwards and back- wards (Fig. 288, de). Owing to the distri- bution of the central apparatus in the central portions of the spinal chord, that is, in the gray columns which pass off from the region of the central canal (c), the white medullary mass, which consists of nerve-fibres, is chiefly placed towards the exterior, forming longitudinal columns, which are partly separated from one another by the anterior and posterior longitudinal fissures (ab), and partly by the points at which the roots of the nerves pass out (g hi). This arrangement of the white matter is a peculiarity of the spinal chord, and is also a point of difference between it and the ventral chord of the Annulata and Arthropoda, which is of great significance. In the Cyclostomata the spinal chord forms a flat band, as it does also in ChiniEera; in most it is more cylindrical in form, and gradually diminishes in size as it passes towards the end of the spinal canal. There are often special enlargements at the points where the larger nerves are given off ; they are very strikingly Fig. 288. Transverse section through the spinal chord of a Calf, a Anterior, b Posterior longi- tudinal fissure. c Central canal. d Anterior, e Posterior cornua. / Substantia gelatiuosa. g Anterior column of the white substance, h Lateral. i Posterior column. 1c Transverse Fig. 2S9. Brain and spinal choi'd of Ortha- gosiscus mola (afrcr
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectanatomycomparative
