. Cunningham's Text-book de l'anatomie. L'anatomie. L'STATUEE DU BEALN". 513 partie représente le rudiment de l'encéphale ou du cerveau ; et le reste du tube sera converti dans la medulla spinalis. Si l'on tente d'analyser la signification de l'élargissement du cerveau rudiment il sera dû en grande partie au fait qu'il n'est ajouté à la marge de la plaque médullaire (voir Eig. 442, E, p. 501) la matière à partir de laquelle la partie sensible de l'œil et le nerf optique sera élaboré ; mais bientôt après la fermeture du tube neural gonflements irréguliers w
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. Cunningham's Text-book of anatomy. Anatomy. THE STATUEE OF THE BEALN". 513 part represents the rudiment of the encephalon or brain; and the rest of the tube will become converted into the medulla spinalis. If the attempt is made to analyse the meaning of the early broadening of the brain rudiment it will be found to be due in great measure to the fact that there is added to the margins of the medullary plate (see Eig. 442, E, p. 501) the material from which the sensitive part of the eye and the optic nerve will be developed; but soon after the neural tube is closed irregular swellings will make their appearance around the attachments of the nerves of smell, vision, hearing, and taste (Eig. 454), Optic tract Tectum mesencephali I I Red nucleus Tectospinal tract B , . Rubro-spinal tract Metathalamus Thalamusy _Brachium conjunctivum , , «» Lemniscus medialis - •- Lemniscus lateralis Cerebellum Corpus striatum erebral hemisphere erebro-spinal ^^"^ tract -''" ~~i Olfactory nerve., / Olfactory epithelium -Brachium pontis Vestibulo-spinal tract s Nucleus gracilis. Medulla oblongata B^ Fibres of posterior funiculus x indicates the place where a tract crosses the median plane Fig. 45L—Diagram representing the connexions of some important Sensory and Motor Tracts in the Brain to which references are made in pages 513 to 517. Motor paths in red ; sensory in other colours. and also the great vagus nerve that is widely distributed to the viscera of the neck, thorax, and abdomen. But there are other factors besides these irregularities of growth of its walls which add complexity to the form of the encephalon in the embryo. In the course of their growth both parts (encephalon and medulla spinalis) of the neural tube undergo great extensions in length, breadth, and thickness; but in the case of the spinal medulla it is the increase in length that is most distinctive, whereas in the encephalon, the irregular expansion in breadth and thickness is more obtrusive. Ne
