ALIMENTARY SYSTEM. 669 



(2) The twelfth cranial nerve or hypoglossal, lying at first close to the 



ninth, tenth, and eleventh, turning, however, to the muscles of the 

 tongue. 



(3) The tenth cranial nerve, the pneumogastric or vagus, lies outside 



the carotid artery, and gives off a superior laryngeal to the larynx 

 with a depressor branch to the heart, an inferior or recurrent 

 laryngeal which loops round the subclavian artery and runs 

 forward to the larynx, and other nerves to the heart, lungs, and 

 gullet. 



(4) The cervical part of the sympathetic, lying alongside of the trachea, 



with two ganglia. 



(5) The great auricular, a branch of the third spinal nerve, running to 



the outer ear. 



(6) The phrenic nerve, a branch of the fourth cervical nerve, with a 



branch from the fifth and sometimes from the sixth, runs along 

 the backbone to the diaphragm. 



For details as to these nerves, the student should consult the practical 

 manuals of Marshall and Hurst and of Parker. 



As to the sense organs little need be said, for their general structure is 

 like that of other Vertebrates, while the detailed peculiarities are beyond 

 our present scope. 



The third eyelid, present in all mammals except the Cetaceans and 

 the Primates, is well developed. The lachrymal gland (absent in 

 Cetacea) lies under the upper lid, and the lids are kept moist by the 

 secretion of Harderian and Meibomian glands. The external ear or 

 pinna is conspicuously large. The cochlea of the inner ear is large and 

 spirally twisted. The nostrils are externally connected with the mouth 

 by a characteristic cleft lip. The tongue bears numerous papillae with 

 taste bulbs. The long hairs or vibrissoe on the snout are tactile. 



Alimentary System. 



In connection with the cavity of the mouth we notice the 

 characteristic dentition, the hairy pad of skin intruded in 

 the gap between incisors and premolars, the long and 

 nairow, in part bony, palate separating the nasal from the 

 buccal cavity, the muscular tongue with its taste papillae, 

 the glottis which leads into the windpipe, and the bilobed 

 flap or epiglottis which guards the opening, the paired 

 apertures of the Eustachian tubes opening into the posterior 

 nasal passage, the end of this passage above the glottis, 

 and the beginning of the pharynx. Less obvious are the 

 organs of Jacobson, paired tubular bodies lying enclosed in 

 cartilage in the front of the nasal chamber, and communi- 

 cating on the one hand with the nostrils, and on the other 

 hand with the mouth by two naso-palatine canals which open 

 a little way behind the posterior incisors. Opening into the 



