CHAPTER VII 



THE MEDULLA OBLONGATA AND CEREBRAL NERVES 



CONTENTS. 1. General anatomy of the brain : the medulla oblongata. 2. Motor 

 functions of hypoglossus nerve. 3. Vago - accessory group ; motor functions 

 of eleventh nerve. 4. Different functions of vagus nerve. 5. The glosso- 

 pharyngeal exclusively a nerve of taste. 6. Functions of the facial and acoustic 

 nerves. 7. Functions of the oculometer and trigeminal nerves. 8. The medulla 

 oblongata as a motor centre. 9. The medulla oblongata as the central organ 

 of locomotion and posture. 10. The medulla oblongata as a sensory centre. 

 Bibliography. 



IN the lower vertebrates the spinal cord alone suffices, as we have 

 seen, for the regulation of all the functions of animal life. The 

 lowest vertebrate, Amphioxus, possesses only a spinal cord divided 

 into metameres, the higher of which, according to Kupffer's 

 recent work, represent a rudimentary brain, although they have as 

 yet acquired no functional importance greater than or different to 

 the other metameres (Steiner). In the series of Craniota, on the 

 contrary, the constituent parts of the brain are added to the spinal 

 cord by the progressive development of the organism. In man, 

 the highest member of the animal scale, the brain is so highly 

 developed that the spinal cord seems in comparison to be merely 

 its appendage. 



I. From the physiological point of view the brain may be 

 divided into parts, corresponding with those which can be dis- 

 tinguished at an early stage of its development. 



At the head end of the primitive neural tube the first signs of 

 the brain appear as three dilatations, which are transformed into 

 vesicles, destined later to form the cerebral ventricles. The anterior 

 and posterior vesicles each divide into two, while the median 

 vesicle remains undivided. The three primary cerebral vesicles 

 thus form five secondary cerebral vesicles, which again give rise 

 from before backwards to : 



(a) The fore-brain or prose ncephalon. In the embryo this is 

 represented by the 1st secondary vesicle, which is originally very 

 small and afterwards grows out laterally, forming the hemispherical 

 diverticula. In the adult it is represented by the brain proper or 



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