HISTORY AND METHODS OF INVESTIGATING. 11 



uration often is in the lower vertebrates, yet the inner structure, 

 particularly of those regions of the brain lying caudad of the 

 optic lobes, is often not less complicated than is the case in 

 mammals. The cells and fasciculi of fibres which are necessary 

 for the accomplishment of the simplest motor, sensory, or psychic 

 function must everywhere be the same, and even in the larvae of 

 the cyclostomata they are no longer perfectly simple and easily 

 comprehended. 1 have, therefore, endeavored, in order to come 

 nearer to a solution of the questions before us, to unite the 

 method of comparative anatomy with that of studying the de- 

 velopment of the medullary sheath. We can now stain and 

 trace out each individual medullary sheath. In fact, it was by 

 the method of comparative embryology that we succeeded in 

 discovering the desired primitive conditions in the embryos of 

 the lower animals, and were able to distinguish a number of 

 nerve-tracts which are common to all vertebrates. 



You see, gentlemen, the goal can be reached in many ways. 

 In the case of every new question proposed, we must ask our- 

 selves which method is the best to use, and, above all, where 

 we may expect to find the simplest conditions. Seldom will an 

 examination of the adult human organ attain the object in view. 

 More often we shall be compelled in some way to bring about 

 by artificial means a less complicated state of affairs. 



From time to time it has been attempted to embrace all 

 that was known in regard to the finer structure of the central 

 nervous system in a diagrammatic representation. The oldest 

 diagrammatic representation of the fibres of the brain with 

 which I am acquainted is to be found in DCS Cartes' t: Tracta- 

 tus de Hominc," which appeared in 1662. Of the newer works 

 belonging to this category are the diagrams of the spinal cord 

 by Kolliker, Ludwig, Bidder and Leydig, and the" celebrated 

 diagram of B. Stilling. The plates of Mcvncrt embrace a 



o * 



larger field (from the spinal cord to the corpora quadrigemina), 

 and those of Aeby, Flechsig, and Jelgersma (the whole central 

 nervous system). 



In the following lectures, gentlemen, you will regard 



