TEANSACTIONS OF SECTION D. 775 



in a direct way to the internal organs of the body. The nerves of the extremities 

 reach by the shortest route their territory-, and oulj^ by-and-by they are drawn out 

 to their terminal length. 



By secondary dislocations the nerve-trunks can be curved, and so the direction 

 of their actual end and of thehr growing out can be altered. This is to bo seen in 

 the facial nerve and in many other nerves of the body. When the different 

 nerves that are near together grow out in a different direction they will cross, 

 partly unite, and form anastomoses. The relations in the angle between the head 

 and the body give a striking illustration to this assertion. 



An outgrowing nerve can find obstacles in its straight way. In this case it 

 will undergo a deviation, and this deviation, not being the same for all its fibres, 

 ■will bring about a division of the trunk. Cartilages, blood-vessels, and similar 

 things act as such obstacles. The nerves are not all formed at the same time, 

 the nerves of the neck and of the hind part of the head being formed the first. 



I have not followed as yet the history of the ramified processes of the nerve- 

 cells. They are formed much later than the cylinder-axis fibres, and the con- 

 ditions of their spreading out will be found moie complicated. Every one of these 

 fibres must have one cell as origin, but it seems to me very improbable that it 

 must generally have also terminal cells, and in this point I agree with the opinions 

 of Mr. Golgi and Mr. Forel. 



I should now enter upon the discussion of the morphological position of the nerves. 

 This, however, would take me too long, because different principles would have to 

 be fixed, and I confine myself therefore entirely to the facts I communicated. I 

 shall only give one general remark — I could show that the way which Nature foUows 

 in forming the nervous system is very simple. There is nothing more simple than 

 the formation of the process of a cell, nothing more simple than the straight out- 

 growing of these processes until they find an obstacle, or until they come to a 

 terminal station. Nothing can be, I dare say, more rough than the fact that 

 apparently accidental things, as a blood-vessel or a cartilage, should have an 

 influence on the final arrangement of the nerves of the body. And this final 

 arrangement gives at last a system of the most comphcated organisation — a system 

 which determines all our functions, both of body and of mind. And this system 

 shows itself in the most delicate dependence on the general law of heredity. 



The primary foldings of the blastoderm are of no less simplicity ; their next 

 consequences are to a great extent comparable to the consequences indicated by 

 the geologist in the formation of our earth's crust ; and nevertheless they deter- 

 mine all the further development of the body. 



We can pronounce the general proposition that in her way to the formation of 

 higher organisms Nature is not only passing through simple forms, but she is also 

 using the most simple mechanical means ; and I must think that in the great ques- 

 tion of heredity the study of this means must obtain its full place. 



4. The Moiyliology and Physiology of the Limh-jjlexuses.^ 

 By A. M. Patekson, M.I). 



In bringmg this subject before the Section my object is not so much to enter 

 into details regarding the plexus formation in mammals as to state the broad out- 

 lines of the results of some recent researches, and, if possible, to raise a discussion 

 on the physiological and morphological aspects of the question. 



These plexuses are constant in their presence in higher vertebrates, but no satis- 

 factory reason for their existence is assigned either by the anatomist or the physio- 

 logist. The object of my mquiry is, why do they exist ? Why does not any 

 given nerve (e.t/., the human anterior crural) spring from a single primary division 



' Tliis paper contains a summary of parts of two already published : — (1) Journal 

 of Anatomy and Physwlogy, vol. xxi., 1887, ' On the Limb-plexuses of Mammals ' ; (2) 

 Quarterly Journal of Microscopical Science, August 1887, ' On the Fate of the 

 Muscle-plate, and the Development of the Spinal Nerves and Limb-plexuses in Birds 

 and Mammals.' 



