XI FUNCTIONS OF THE SPINAL BULB 519 



half of the leffc retina and the nasal half of the right retina. 

 This arrangement is essential to the eye as a sense 

 organ with reference to what we have previously spoken 

 of as " corresponding points and single vision with two 

 eyes " (see p. 445). Going through the optic cliiasma, 

 there are also fibres joining one side of tlie brain to the 

 other via the optic tracts and probably fibres joining the 

 two eyes. 



13. The Functions of tlie Spinal Bulb or Medulla 

 Oblongata. — The bulb plays so important a part in the 

 economy of the body that we may almost enumerate its 

 functions by recalling all the instances in which we have 



Fig. 167. — Diaokam to illustrate the Decussation of Fibres in the 

 Optic Chiasma. 



R, right eye; i, left eye; R.Op. f-ight optic tract; L.Op. left optic 

 tract. The decussation is shown by the distribution of the right (shaded) 

 and the left (unshaded) tract to the retinas of the two eyes. 



made mention of its activities in the earlier lessons of this 

 book. Thus we have seen that it contains a centre which 

 gives rise to the contractions of the respiratory muscles 

 and keeps the respiratory pump at work, so that injuries 

 to the bulb may arrest the respiratory process (p. 158). 

 Further it contains centres for the regulation of the 

 heart-beat (p. 77) and of the condition of the blood-vessels 

 over the whole body (p. 69). But beyond these the bulb 

 also contains centres for the nervous act of swallowing, 

 for the reflex secretion of saliva, and for many other 

 actions. Thus we find that simple puncture of, one side 



