430 FUNCTIONS OF THE SENSORIUM COMMUNE, [ch.iv. 



the same opinion;^ the celebrated Camper said, that if the 

 sensorium commune has a seat at all, it ought to be in the 

 pineal gland, and in the nates and testes, and that, therefore, 

 the opinion of Des Cartes was not so very absurd.^ It certainly 

 does not appear that the whole of the cerebrum and cerebellum 

 enters into the constitution of the sensorium commune, which 

 portions of the nervous system seem rather to be the instru- 

 ments that the soul directly uses for performing its own actions, 

 termed animal ; but the sensorium commune, properly so called, 

 seems not improbably to extend through the medulla oblongata, 

 the crura of the cerebrum and cerebellum, also part of the 

 thalami optici, and the whole of the medulla spinalis; in a 

 word it is co-extensive with the origin of the nerves. That 

 the sensorium commune^ extends to the medulla spinalis is 

 manifest from the motions exhibited by decapitated animals, 

 which cannot take place without the consentience and interven- 

 tion of the nerves arising from the medulla spinalis ; for the 

 decapitated frog, if pricked, not only withdraws the punctured 

 part, but also creeps and leaps, which cannot be done without 

 the consensus of the sensorial and motor nerves, the seat of 

 which consensus must necessarily be in the medulla spinalis 

 — the remaining portion of the sensorium commune. 



The reflexion of sensorial into motor impressions, which 

 takes place in the sensorium commune, is not performed ac- 

 cording to mere physical laws, where the angle of reflexion is 

 equal to the angle of incidence, and where the reaction is equal 

 to the action ; but that reflexion follows according to certain 

 laws, writ, as it were, by nature on the medullary pulp of the 

 sensorium, which laws we are able to know from their eff'ects 

 only, and in nowise to find out by our reason. The general 

 law, however, by which the sensorium commune reflects sen- 

 sorial into motor impressions, is the preservation of the individual; 

 so that certain motor impressions follow certain external impres- 

 sions calculated to injure our body, and give rise to movements 

 having this object, namely, that the annoying cause be averted 



' Advers. Med., p. 15 ; Vermisch. Schrift., Iten Bandes, Seite 56. 



' Kleine Schriften, (Leipzig, 1782,) Iter Band; Nachricht von der Zergliederung 

 eines jungen Elephanten., § 21. 



^ Marherr contends that the medulla spinalis ought also to be referred to the 

 sensorium commune in * Praelect. ad Inst. Med. Boerhaavii,' tom. ii, p. 404. 



