288 A Manual of Veterinary Physiology. 



tongue, and having special nerve-endings, known as ' taste- 

 bulbs,' in the circumvallate papilla (see ' Taste '). 



Tenth Pair, or Pneumogastric. — This is both a sensory and 

 motor nerve. At its origin it is intimately mixed up with 

 the ninth, eleventh, and twelfth pairs of nerves, and later 

 on with the sympathetic. It is the most extensively dis- 

 tributed nerve in the body, supplying respiration, heart, 

 and digestive systems. 



The sensory branches of the nerve are not highly en- 

 dowed with sensation, probably for the reason that their 

 chief function as sensory nerves is as afferent channels for 

 reflex action. The motor fibres are joined by some from 

 the spinal accessory, facial, and lingual. 



The various branches of the vagus may be best studied 

 by taking them in the order in which they are given off'. 

 The pharyngeal branch, through the pharyngeal plexus, 

 supplies motor power to the pharynx (and in the horse 

 supplies the cervical portion of the oesophagus with motor 

 power), derived, it is said, from the spinal accessory nerve. 

 The superior laryngeal furnishes the interior of the larynx 

 with sensibility. The external laryngeal supplies motor 

 fibres to the crico-thyroid muscle, the lower constrictor of 

 the pharynx, and in a minor degree the anterior portion of 

 the oesophagus. In the horse the crico-thyroid muscle is sup- 

 plied by the first cervical nerve (see ' Voice '). The inferior, 

 or recurrent, laryngeal is given off' from the main trunk 

 within the chest, on the left side winding around the aorta 

 from without inwards, and on the right side passing around 

 the dorso-cervical artery; both branches return up the neck 

 and supply all the muscles of the larynx (excepting the 

 crico-thyroid) with motor power. The branches are •'!' 

 great practical interest, inasmuch as they are affected (espe- 

 cially the left) in that common form of disease in horses 

 known as 'roaring,' which is generally due to paralysis and 

 atrophy of the muscles which dilate the laryngeal opening. 

 After division of the recurrent nerves death by asphyxia 

 is likely to follow. I have observed complete bilateral 

 paralysis of the larynx in horses without asphyxia being 



