CH. XLTV.] INTERIOR OF THE BULB. 63! 



nucleus of the ninth, tenth, and eleventh nerves. Fibres from 

 this nucleus run from the ventral surface through the reticular 

 formation in a series of bundles, and it emerges from a groove 

 between the anterior pyramid and olivary body. It is connected 

 with the vagus, with the superior cervical ganglion of the sympa- 

 thetic and with the upper cervical nerves. 



Distribution. This nerve is the motor nerve to the muscles 

 of the tongue (stylo-glossus, hyo-glossus, genio-hyo-glossus, and 

 linguales). The branches of this nerve to the genio-hyoid, thyro- 

 hyoid, sterno-thyroid, sterno-hyoid, and omo-hyoid are branches 

 of the first, second, and third cervical nerves carried down in its 

 sheath and slipped off at various points as descendens (hypoglossi) 

 cervicis, &c. 



The reader should now turn once more to fig. 464 (p. 626) 

 and try to obtain a more general idea of the nuclei of origin 

 of all these nerves. It will be noticed that the centres of 

 afferent nerves (coloured red) are in the minority ; these com- 

 prise the sensory nucleus of the fifth, the nuclei of the eighth 

 nerve, and the glosso-pharyngeal and vagal portions of the com- 

 bined nucleus of the ninth, tenth and eleventh nerves. The 

 remaining nuclei (coloured blue) are efferent, and may be princi- 

 pally arranged into two groups : (i) the nuclei of the third, 

 fourth, sixth and twelfth nerves which are close to the middle 

 line, and (2) the motor nucleus of the fifth, seventh, and nucleus 

 ambiguus (motor nucleus of ninth and tenth nerves) which form 

 a line more lateral in position. 



A mere enumeration of the destination of the nerves arising 

 in the bulb shows how supremely important this small area of the 

 brain is for carrying on the organic functions of life. It contains 

 centres which regulate deglutition, vomiting, the secretion of 

 saliva, sweat, &c., respiration, the heart's movements, and the 

 vaso-motor nerves. 



The Internal structure of the Bulb, Pons, and 

 Mid-brain. 



The structure of the interior of these parts is best studied 

 in a series of transverse sections. We will limit ourselves to 

 seven, the level of which is indicated in fig 465. The cerebellum 

 has been bisected into two halves and turned outwards, its upper 

 peduncles cut through to render the parts more evident. The 

 position of our seven sections is indicated by the transverse lines 

 numbered i to 7. 



