888 THE MEDULLA OB LONG AT A. 



chloride solution, or a crystal of kreatin placed on the floor of the fourth 

 ventricle of the frog, produces, after a minute or so, a cry which ushers in a 

 seizure, during which the fore-limbs are crossed under the sternum, the hind- 

 limbs at first flexed at hip and extended at knee and ankle, until the animal 

 rolls backward. Then extension at hip follows. The muscular contraction, at 

 first clonic, later becomes tonic. The whole seizure lasts about one minute. 

 The seizure is less intense, if the cerebral hemispheres have previously been 

 removed. Convulsions cannot be similarly excited from the spinal cord 

 itself. 



It is in the bulb that nerve cells are met that more than any others 

 in the neural axis seem to have automatic in contradistinction to reflex 

 activity. The bulbar respiratory cells, like the muscle cells of the 

 heart, seem to be able to rhythmically convert stores of their potential 

 into kinetic energy apart from any spur by external stimuli, although 

 profoundly responsive to these latter. 



The bulb is indicated by various data as the part of the nervous system 

 in which has been earliest developed, on a grand scale, that kind of com- 

 munion between constituent neural units, which concentrates function 

 and combines in co-ordination a number of various working factors. 

 There seem to have been early centred in it regulating nervous mechan- 

 isms for certain reactions of fundamental import to the very existence 

 of the individual. It thus gave, so to say, opportunity and guarantee 

 for the response of the neural axis in front of it to the call for building up, 

 in the course of ages, under the direction of the sense organs, especially 

 those of sight and smell, the organs of perception, memory, and intellect, 

 with culmination in the mammalian cerebrum and mind. On the other 

 hand, behind it, somewhat similarly, proceeded a development of neural 

 mechanisms for a great senso-motile organ, the skeletal musculature with 

 its bony levers and its overlying skin, each lateral half of which may be 

 considered as equivalent to the senso-motor mechanism of one eye or 

 of one ear. As vertebrate evolution has gone on, the great motile organ 

 has come more and more to lie at the disposal of the upper hierarchies 

 of nerve powers composing the supreme senses, especially the visual 

 with all its spatial quality. Hence the bulb stationed between these 

 two developments is threaded by strands for their conjunction, path- 

 ways for travel up and down between them. 



Concerning the bulb as a conductor, the following resume must suffice. 

 There descends into the cord, from the opposite half of the mesencephalon, 1 a 

 path that probably co-ordinates movements of the body with stimuli impinging 

 on the retina. From the end stations of the vestibular nerve 2 there descends 

 into the cord an uncrossed path, that probably relates the body movements with 

 the sensations originated in the semicircular canals. Paths also, both uncrossed 

 and crossed, descend into the cord from the red nucleus 3 and the large diffuse 

 nuclei of the reticular 3 formation of both middle and hind-brain ; the functions 

 of these are even more conjectural. In mammals a path descends from the cere- 

 bral hemisphere into and through the bulb to reach the motor root cell system. 

 This makes the pyramids, and is largest in the highest forms of nervous 

 system. It appears wanting in vertebrata below mammals (Singer, 188 1). 4 



1 Held, Neurol. CentralbL, Leipzig, 1890, Bd. ix. S. 481; Arch. f. PhysioL, Leipzig, 

 1893, S. 254 ; Boyce, Phil. Trans., London, 1895, vol. clxxxvi. p. 321 (communicated 1894). 



2 See Ferrier and W. A. Turner, Phil. Trans., London, vol. clxxxv. 



3 Neurol. CentralbL, Leipzig, 1890, Bd. ix. S. 481. 



4 Sitzungsb. d. k. Akad. d. Wi&sensch., Wien, 1881, S. 393 ; Pitres, Arch, de physiol. 

 norm, et path., Paris, 1886, Se"r. 3, tome vii., and others. 



