482 GENERAL ANATOMY. 



rapid, becomes much slower: after the internal ear and the 

 eye, it is the part of the body which then grows the most 

 slowly. 



In old age, the nervous system experiences a sensible dimi- 

 nution in volume, which manifests itself in the encephalon by 

 the narrowing of the cranium,* and that can be established 

 also by measuring the spinal marrow. 



765. The nervous system is also subject to many errors 

 of conformation. t One case is known of a total deprivation 

 of the nervous system: it has been observed in an acepha- 

 lous foetus reduced to a little trunk without form. There are 

 several cases of the absence of the encephalon and of the head. 

 There are a great many cases of the total absence of the nerv- 

 ous centre, the nerves and the spinal ganglions existing. 

 There are a still greater number of casesof theabsenceof the en- 

 cephalon, the spinal marrow existing, as well as all the nerves 

 of the face and neck. The spinal marrow may remain open, 

 hollow, or extended throughout the whole canal. In certain 

 cases the cerebellum and tubercles exist, as well as the crura 

 cerebri and their optic and striated enlargements, and the 

 hemispheres alone are wanting. In some cases the hemispheres 

 are incomplete ; the middle and posterior lobes are deprived 

 of furrows and convolutions. Sometimes the corpus callosum 

 only is wanting ; J or there remains a cavity within the hemi- 

 sphere, or in the septum, &c. The cerebellum may present 

 analogous defects, especially in the number of its laminae. 

 All these cases are imperfections or defects of development. 



* Tenon, RecJierches sur le Crane humain, Mem, de Plnst. sc. phys. et 

 Math., tome I. 



f A Beclard, Memoire sur les foetus actphales; Paris, 1815. Geoffrey 

 Saint-Hilaire, Phibs. anatom., vol. ii. Breschet, Diction, de Med., art. 

 ActpTiale, et Jlnencephale. C. P. Ollivier, d* Angers, Essaie sur Fanatomie et 

 le* vices de conformation de la moelle tpiniere,- Paris, 1823. Id. Traitt de la 

 moelle tpiniere et de ses maladies, un. vol. 8vo. Laroche, Essaie d'anat. 

 patfiol , sur les monstruosites de la face,- Paris, 1823. 



|Reil, Jircliw.fur die physiologic, torn. xi. 



Malacarne, Neuro encephaktomia,- Pavia, 1791. 



