;io MAMMALIA. 



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 branches 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 



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 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 vibrissse 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 pre- 

 molars, the long and narrow, in part bony, palate separating 

 the nasal from the buccal cavity, the muscular tongue with 

 taste papillae, the glottis leading into the windpipe, the 

 bilobed epiglottis guarding 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. The organs of Jacobson are 

 paired tubular bodies, vascular and richly innervated, lying 

 enclosed in bone in the front of the nasal chamber, and 

 communicating with the nostrils above, and on the 

 other hand with the mouth by two naso-palatine canals 

 which open behind the posterior incisors. Opening into 

 the mouth and conducting 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 





