594 DEVELOPMENT OF THE BRAIN IN THE FCETUS. 



ordinarily called the nerve, as but a commissure to connect it 

 with the brain.* 



Development of the Brain in the Foetus. 

 In their course of development in the foetus, the spinal 

 Fig. 226.f marrow and brain present many 



A "phases of structure, which cor- 



respond to a considerable extent, 

 with the perfect forms of these 

 parts in many of the inferior ani- 

 mals. Two minute longitudinal 

 C cords, with five pairs of gangli- 

 onic swellings at their upper or 

 anterior parts, constitute all that 

 exists of the cerebro-spinal axis in 

 a human embryo of seven weeks. 



* The student will find his progress, in the difficult study of the nervous 

 system accelerated by the possession of preparations upon which the nerves have 

 been prepared and dried ; or what is next best, by drawings, which, at the same 

 time that they are kept in the main true to nature, give to the subject, some- 

 thing of the clearness of a diagram. In the latter respect, the student will 

 derive considerable assistance from the " Plates of the Cerebro-Spinal Nerves, 

 with references," by Dr. P. B. Goddard ; in Manec's two plates, of the cerebro- 

 spinal axis, and of the sympathetic nerve, the size of life ; and in Professor 

 Lobstein's treatise, "De structura, usu, et morbis, nervi sympathetic!," the 

 three last of which have been translated with additions, by the editor of this 

 work. Quain's anatomical plates which have also been issued under the super- 

 vision of the editor, by Carey & Hart, of this city, will be found to contain not 

 only a complete exhibition of the nerves, but of all the parts of the human body. 



f Anatomic du Cerveau, &c. par F. Tiedemann. 

 f Fig. 226. A. 



Side view of the brain and spinal marrow of a foetus of seven weeks, a. 

 Hemispheres of the cerebrum, a'. Corpus striatum and optic thalamus. b. 

 Mass, from which is subsequently formed the tubercula quadrigemina. c. Ce- 

 rebellum', k. Spinal marrow enlarged at the top where it forms its bulb d. 



B. 



Brain of a fetus of twelve weeks, d. Spinal marrow, expanded and curved 

 above, forming the medulla oblongata. c. Cerebellum, below which is seen 

 passing one of the ascending cords of the medulla, b. Mass of the tubercular 

 quadrigemina. The crus of the cerebrum is seen directed downward and for- 

 ward, a. Hemispherical sac. 



C. 



Brain and spinal marrow of the same foetus seen from behind, d. Medulla 

 spinalis. c. Cerebellum, a. Hemispheres of the brain, b. Mass of the tuber- 

 cula quadrigemina. 



