454 CETACEA. 



hyal by tortuous openings through valvular passages. This compound sac extends 

 to the middle line, its JB.rst portion running along the inner surface of the stylohyal 

 to its extremity, where its inner wall lies against the upper surface of the caratohyaL 

 Thus, the sacs of opposite sides are here only separated from each other by a thin 

 layer of connective tissue, — so thin, indeed, and the sacs presenting so many crypts 

 that might communicate with their fellows of the opposite sac, that I had at first 

 expected to have met with the anomaly of the Eustachian tubes communicating 

 with each other at the base of the tongue. The second portion of the compound 

 sac hes between the thyrohyal and the lower portion of the thyroid cartilage, and 

 extends in front of the latter, and the sacs of opposite sides are here also only separated 

 by a narrow interval of connective tissue. In the most anterior portion of the sac, 

 that lying between the caratohyal and stylohyals, I have found small bones, and, 

 strange to say, many crystalline lenses of fishes of apparently one size and probably of 

 one species ; and from one individual I removed two parasitic worms, Ascaris simplex, 

 which is so prevalent in the stomach and intestines. The whole of this remarkable 

 sac has its walls covered with valvular folds defining crypts and passages, and, at 

 the commencement of the portion lying between the thyrohyal and thyroid cartilage, 

 valvular folds are connected to each other by fine fibrous cords (PL XXVIII, 

 figs. 2 and 5). 



The orifices in the posterior nares lie anterior to the epiglottis when in its 

 normal position, and the downward direction of the external passage is to guard 

 against the possibility of water finding access by them to the Eustachian system, and 

 the valves subserve the same purpose. Still, nature, in avoiding one danger, has in- 

 curred another in the apparent tendency which the sacs have to become receptacles 

 for foreign objects drawn up from the throat in the act of expiration, and which by 

 their presence might prove the cause of inflammation and abscesses in the ramifica- 

 tions of the Eustachian system and at the root of the tongue. These foreign objects 

 may doubtless find their way first into the posterior nares by the action of the mus- 

 cles which grasp the epiglottis. 



Microscopic structure of the avails of Eustachian sacs. — The very remarkable 

 pouched character of the walls of the foregoing passage and their glutinous surface 

 led me to investigate their minute structure {vide PI. XXXVII, figs. 7 and 8). 

 I find them to be throughout composed of loose folds of thick mucous membrane. 

 Short irregular papillae invest the surface, and everywhere, at scattered intervals, are 

 small pits and the minute orifices of mucous glands. These glands are most of them 

 superficially situated, but some are sunk deeper into the tissue, chiefly simple and 

 tubular. Certain of them nevertheless are sKghtly racemose ; and all contain cylin- 

 drical epithelium with often a central cavity. The elevated papillge already men- 

 tioned are exceedingly vascular, indeed possess a thick network of fine capillaries, 

 the parent vessels of which are both numerous and of considerable calibre. This 

 tube, therefore, must at times be very turgid. The free surfaces of the papillae are 

 themselves quite shaggy under the microscope, being covered by a close-set layer of 

 cylindrical fringed or ciliated epithelium. The deep connective tissue of the sub- 



