The Digestive System. 77 



distributes visceral motor branches to certain muscles (masticatory 

 group, mylohyoid and digastric) regarded as belonging to this, the 

 first arch. A visceral sensory connection with the mouth is con- 

 sidered to be formed by the lingual branch of the mandibular nerve 

 and by the palatine branches of the spheno-palatine ganglion. 

 Both are, however, connected with the central nervous system 

 through the seventh nerve, the former by the chorda tympani, 

 and the latter by the great superficial petrosal. 



The seventh, or facial nerve, is the nerve of the second, or 

 hyoid arch. ' 1 1 is chiefly distributed as a visceral motor nerve to the 

 cutaneous muscles of the head, but contains also taste fibres from 

 the tongue. The ninth, or glossopharyngeal nerve, belonging 

 to the third arch, the tenth, or vagUS, belonging to the fourth and 

 succeeding arches in lower forms, and the eleventh, or spinal 

 accessory nerves, the latter apparently related to the vagus as a 

 motor portion, are distributed as visceral motor nerves to the 

 pharyngeal and laryngeal musculature, and as visceral sensory 

 nerves to various visceral organs, the ninth nerve supplying the 

 gustatory organs of the tongue. The vagus contains a variety of 

 fibres, both afferent and efferent, the former from the larynx and 

 respiratory organs, the latter distributed to the organs of circulation 

 and digestion. The spinal accessory has a characteristic distribu- 

 tion to the cleidomastoid, sternomastoid and trapezius muscles of 

 the side of the neck and shoulder. The twelfth, or hypoglossal 

 nerve has the relation of the ventral or motor portion of a spinal 

 nerve, and is distributed as a motor nerve to the muscles of the 

 tongue. 



THE DIGESTIVE SYSTEM. 



The digestive system comprises as its chief portions the 

 digestive tube and the digestive glands. The digestive tube is 

 divisible into "several parts, which, with the exception of the caecum 

 and its vermiform process, are arranged in a linear series. The 

 digestive glands comprise the oral glands, the liver, and the 

 pancreas. They are parts of an extensive series of epithelial 

 glands, otherwise contained within the wall of the tube, and for 

 this reason not appearing as gross structures. 



