REFLEX PATHS. 393 



in doubt; it may be established in part (i) by the fornix, the 

 thalamo-mammillary bundle and thalamo- spinal fibers, (2) by 

 the fornix, medullary stria, fasciculus retroflexus and descending 

 fibers of the interpeduncular ganglion, and, (3) by the fornix and 

 the pedunculo-mamillary bundles. Squinting, due to bright light, 

 is produced by an arc composed of the visual path, the corticifugal 

 part of the occipito-thalamic radiation, the anterior longitudinal 

 bundle and the facial nerve. Substitute the oculomotor nerve 

 for the facial and we have the arc for pupillary contraction under 

 the same conditions. 



Salivary reflexes, in which the sight of a fine dinner or the smell 

 of it causes the flow of saliva ; coughing, sneezing, vomiting reflexes 

 and deglutition reflexes are complicated, but, knowing the nerve 

 supply of the parts involved, the student should try to trace the 

 impulses. 



(3) Spino-cerebral Reflexes. Impulses received by the spinal 

 cord through the afferent fibers of its nerves are transmitted by 

 the medial longitudinal bundle, the fasciculi proprii and formatio 

 reticularis to the nuclei of motor cerebral nerves. Thus is brought 

 about the movement of the head and eyes toward the source of 

 impulse, a change of facial expression to agree with the painful 

 or pleasing character of the impulses, etc. 



(4) Cerebro-spinal Reflexes. Of these there are many. Let 

 us notice three. 



Respiratory Reflex. Any obstruction or irritation in the larynx 

 or trachea sends an impulse through the vagus nerve to its sensory 

 nucleus and, through its descending branches, in the solitary 

 tract, to the nucleus ambiguus and nucleus of the phrenic nerve 

 in the cervical cord, causing increased respiratory efforts, coughing, 

 spasm of muscles closing glottis, etc. 



Equilibrium Reflex (Vestibulo-spinal Reflex). The simplest 

 arc of equilibrium between the eighth cerebral nerve and the 

 spinal nerves is formed by the neurones of the vestibular ganglia 

 (Scarpa's), the vestibulo-spinal part of the descending anterior 

 cerebello-spinal tract and the motor neurones of the anterior 

 columna of the spinal cord. A more complicated arc includes 

 the descending root of the vestibular nerve, the external arcuate 



