LUNGS. 333 



The lachrymal gland resembles the mammary and salivary 

 glands and the pancreas, in this respect, that the ducts ramify 

 with a certain degree of regularity, the principal trunk giving 

 off branches laterally at certain intervals, these sending out in 

 the same way side branches, which in their turn afford a third 

 set. No attempt, so far as I know, has hitherto been made to 

 determine the chemical nature of the lachrymal glands. 



4. Most of the other glands are so small in size that their 

 structure has hitherto eluded the observations of anatomists, and 

 the researches of chemists. The glands of the meatus auditorius 

 externus, which secrete the cerumen of the ear, may be mentioned 

 as examples ; also the sebaceous glands, those by which insensi- 

 ble perspiration and sweat are elaborated, and which, from recent 

 observations, seem to have a form somewhat resembling a cork 

 screw. The glands of the larynx, those that secrete mucus, 

 those which elaborate the gastric juice, and many other minute 

 glands, still remain unknown as far as their structure is concerned. 



CHAPTER XXVII. 



OF THE LUNGS. 



THE lungs are the important organs by which respiration is 

 performed ; a function so necessary to life that it cannot be sus- 

 pended even for a few minutes without death. The lungs in 

 man and most quadrupeds are double, one lung being situated 

 on each side of the thorax. Each lung is surrounded by the 

 pleura, and they are separated from each other by two folds of 

 the pleura called the mediastinum. The lungs are connected 

 with the mouth and nostrils by a cartilaginous tube called the 

 trachea. The upper part of this air tube, being so constructed 

 as to constitute the organ of the voice, is named the larynx. It 

 consists of cartilages, ligaments, and muscles, and is lined by a 

 mucous membrane. Besides these there are blood-vessels and 

 nerves, and some glands. The cartilages are the thyroid, cri- 

 coid, and the epiglottis, which shuts the mouth of the larynx, by 

 closing down upon the rima ylottidis, in order to prevent foreign 

 substances from making their way into the lungs. These three 

 are large single cartilages constituting the throat, and very con- 



