312 OF THE ORGANS OF DEGLUTITION. [SECT. 143. 



A Course of Lectures on Dental Physiology and Surgery, London, 1848. 

 R. Owen, Odontography, London, 1840—45, 1 vol., with Atlas of 150 plates, 

 and article 'Teeth,' in Cyclopedia of Anatomy, iv., p. 864. Krukenberg, 

 in MiiiL. Arch., 1849, p. 403. J. Czermak, in Zeitschrift f.w. Zool, 1850, 

 Bd. II. p. 295. Arnold, in der Salzburger Med. Zcitung, 183 1, p. 236. Rasch- 

 kow, Meletemata Circa Pentium Mammalium Evolutionem, Vratisl., 1835. 

 Goodsir, in Edinb. Med. and Surg. Journal, 1838, No.xxxi. 1 ; and Froriep's 

 Neve Notizcn, Nos. 199, 200, 202, 203. Marcusen, in the Bulletin Phys. Math, 

 viii. No. 20, Petersburgh, 1850. Huxley, in the Quart. Journal of Microsc. 

 Science, i. p. 149. Lent, in Zeitschrift f. w. Zool., vi. Hft. i. S. J. A. 

 Salter, in Quarterly Journal of Micr. Science, 1853. On Caries of the Teeth 

 the following may be consulted :— Tomes (I.e.) ; Ficinus, in Journal far Chi- 

 rurqie von Waltlter und Amnion, 1846, p. 1 : and Klenke, Die Verderbniss der 

 Z'dhnc, Leipzig, 1850. A. Pander, De Pentium Structura Diss, iuaug. Pe- 

 tropoli, 1856. A. Hannover, Tiber die Entwickelung tend den Ban des Sauge- 

 thierzahnes, in Nova Acta Nat. Cur., vol. xxv. p. i. Tomes, in Philos. Transact., 

 1856. The Comparative Anatomy of the Teeth, with reference to microsco- 

 pical structure, will be found treated in the above-cited works of Retzius 

 and Owen ; also by Erdl, in den Abhandlungcn der Math. Phys. Klasse, der 

 Kim. Bayer. Altad., Bd. iii., Abth. 2. Tomes, in the Philos. Transactions, 

 1849-50 "(Marsnpialia and Rodentia). Agassiz, Poissons fossiles. Henle 

 and J.Muller, Systemat. Beschreib. der Plagiostomen, 1838. 



III. — Of the Organs of Deglutition. 



1. PHARYNX. 



§ 143. With the pharynx, the digestive tract begins to 

 become more independent, and to assume, a special layer of trans- 

 versely striped muscles, the constrictores and levatores, which, 

 however, do not encircle, it completely, and arise, for the most 

 part, from bones. The thickness of the walls of the pharynx, 

 Avhich is on an average 2'", depends chiefly upon this muscular 

 layer, which is enveloped externally by a tense fibrous coat of con- 

 nective tissue and elastic fibres, and separated internally from the 

 mucous memlrane by a layer of submucous tissue. The mucous 

 membrane is paler than that of the oral cavity, and differs some- 

 what in structure in the upper and lower half of the pharynx, 

 In the latter place, i. e., below the palatopharyngeal arches, or in 

 the part through which the food passes, it possesses a pavement 

 epithelium, of the same structure and thickness as that in the 

 walls of the oral cavity. Above these arches, on the other hand, 

 — consequently upon the posterior surface of the soft palate, the 

 superior surface of the uvula, around the posterior openings of 

 the nares, and the orifices of the Eustachian tubes, and upon the 

 vault of the throat, — the epithelium of the pharynx is ciliated, 



