ALIMENTARY SYSTEM OF THE RABBIT. 557 



(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 for- 

 ward 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 papillee with 

 taste-bulbs. The long hairs or vibrissx 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 narrow, in part bony, palate separating the 

 nasal from the buccal cavity, the muscular tongue with its 

 taste-papillse, 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 

 mouth and bearing the salivary juice, whose ferment alters 

 the starchy parts of the food, are the ducts of four pairs of 

 salivary glands. The parotid, which is largest, lies between 

 the external ear chamber and the angle of the mandible ;, 

 the infra-orbital lies below and in front of the eye ; the sub- 



