RKPORT ON THE PHYSIOLOGY OF THE NERVOUS SYSTEM. 63 



too, has been thrown on the functions of several of the ence- 

 phalic nerves, and especially of those supplying the face and 

 its connected cavities, by Mr. Herbert Mayo, who has analysed 

 their anatomical composition, and pursued their course with 

 singular precision, and has thus been enabled to correct some 

 errors of detail in the system of Sir Charles Bell. 



Nervous System. — In man, and in other vertebrated animals, 

 the nervous system consists of the cerebrum, cerebellum, me- 

 dulla oblongata, medulla spinalis, and of the encephalic, spinal, 

 and ganglionic nerves. It seems most natural to observe this 

 order of anatomical sequence in recording what is known of 

 nervous functions. 



Cerebrum, or Brain-proper. — The physiology of the brain 

 has received of late years very considerable accessions, and its 

 vital offices, viewed as an entire organ, have now probably been 

 ascertained with sufficient precision. Some portion of this newly 

 acquired knowledge has been gathered from experiments on 

 living animals, but the greater and more valuable part has 

 flowed from the study of comparative development. In this 

 latter field of inquiry, Tiedemann's elaborate history of the pro- 

 gressive evolution of the human brain during the period of 

 foetal existence, with reference to the comparative structure of 

 that organ in the lower animals, merits an early and detailed 

 notice. It had been discovered by Harvey, that the foetus in 

 the human species, as well as in inferior animals, is not a pre- 

 cise facsimile of the adult, but that it commences from a form 

 infinitely more simple, and passes through several successive 

 stages of organization before reaching its perfect development. 

 In the circulatory system, these changes have been minutely 

 observed and faithfully recorded*. Tiedemann has traced a 

 similar progression in the brain and nervous system, and has 

 moreover established an exact parallel between the temporary 

 states of the foetal brain in the periods of advancing gestation, 

 and the jiermanent development of that organ at successive 

 points of the animal scale. The first part of his work is simply 

 descriptive of the nervous system of the embryo at each suc- 

 cessive month of foetal life. It constitutes the anatomical grovmd- 

 work upon which are raised the general laws of cerebral forma- 

 tion, and the higher philosophy of the science. In the second 

 part, Tiedemann has established, by examples drawn from all 

 the grand divisions of the animal kingdom, the universality of 

 the law of formation, as traced in the nervous system of the 



• See an excellent Essay on the Development of the Vascular System in the 

 Foetus of Vertebrated Animals, by Dr, Allen Thomson. 



