i;2 VETERINARY PHYSIOLOGY 



for the muscles of the bronchi and alimentary canal, inhibitory 

 to the heart, dilator to blood vessels of the thorax and abdomen, 

 and motor to the muscles of the larynx and to the levator 

 palati. The accessorius is also motor to the sterno-cleido- 

 mastoid and trapezius. 



The IX. (Glossopharyngeus) is essentially a dorsal root, 

 and is the ingoing nerve for the back of the mouth, the 

 Eustachian tube, and tympanic cavity. It transmits outgoing 

 fibres which are motor to the stylo-pharyngeus and middle 

 constrictor of the pharynx. 



The VII. (Facial) is almost purely a ventral root, trans- 

 mitting the motor fibres to the muscles of expression, and 

 secretory fibres to the submaxillary and sublingual glands 

 and the glands of the mouth. It, however, carries ingoing 

 fibres from the anterior two-thirds of the tongue. 



The V. (Trigeminal) is chiefly a dorsal root, but it has a 

 distinct ventral or motor root which joins it, and carries the 

 motor fibres to the muscles of mastication. It is the great 

 ingoing nerve for all the face. 



The VI. (Abducens) supplies the external rectus of the eye. 



The IV. (Trochlearis) supplies the superior oblique. The 

 III. (Oculo-motorius) supplies all the muscles of the eye 

 except those supplied by VI. and IV. The anterior part of 

 the nucleus consists of small cells and gives off fibres to the 

 sphincter pupillse and ciliary muscles. 



The fibres coming from the nuclei of these cranial nerves 

 do not always pass out in the nerve itself. Thus, fibres from 

 the nucleus of the III. to the orbicularis oculi pass out in 

 the VII., while fibres for the posterior belly of the digastric 

 which pass out in the VII. probably come from the nucleus 

 of the XII. 



4. Reflexes of the Medulla 



The extensive series of synapses in the medulla form 

 arrangements by which various combined and co-ordinated 

 movements are controlled. Thus, part of the nucleus of the 

 vagus governs the movements of respiration, while other parts 

 preside over the slowing mechanism of the heart. To these 

 various reflex arrangements the name of centres has been given, 



