710 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 papillee with 
taste bulbs, The long hairs or vibrissze 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 papille, 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 ~ 
