THE PROCTODuEUM. 641 



In Birds the formation of the proctodseum is somewhat more compli- 

 cated than in other types, owing to the outgrowth from it of the bursa 

 Fabricii. 



The proctodseum first appears when the folding off of the tail end of 

 the embryo commences (fig. 429, an} and is placed near the front (originally 

 the apparent hind) end of the primitive streak. Its position marks out 

 the front border of the postanal section of the gut. 



The bursa Fabricii first appears on the seventh day (in the chick), as a 

 dorsal outgrowth of the proctodseum. The actual perforation of the sep- 

 tum between the proctodanmi and the cloacal section of the alimentary tract 

 is not effected till about the fifteenth day of fcetal life, and the approxi- 

 mation of the epithelial layei-s of the two organs, preparatory to their 

 absorption, is partly effected by the tunneling of the mesoblastic tissue 

 between them by numerous spaces. 



The hypoblastic section of the cloaca of birds, which receives the open- 

 ings of the urinogenital ducts, is permanently marked off by a fold from 

 the epiblastic section or true proctodseum, with which the bursa Fabricii 

 communicates. 



BIBLIOGRAPHY. 

 Alimentary Canal and its appendages. 



(561) B. Afauassiew. "Ueber Bau u. Eutwicklung d. Thyinus d. Saugeth." 

 Archlvf. mikr. Anat. Bd. xiv. 1877. 



1562) Fr. Boll. Das Princip d. Wachsthums. Berlin, 1876. 



(563) E. Gasser. "Die Entstchuiig d. Cloakenoffnung bei Hiihnerembryonen." 

 Archiv /. Anat. u. PhysioL, Anat. Abtli. 1880. 



(564) A. Gotte. Beitrdge zar Entwicklungsgeschichte d. Darmkanals imHilhnchen. 

 1867. 



(56^) W. Mtiller. "Ueber die Entwickelung der Schilddriise." Jeiiaische Zeit- 

 schrift, Vol. vi. 1871. 



(.s'6) W. Miiller. "Die Hypobraucbialrinne d. Tunicaten." Jeiiaische Zeit- 

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(567) S. L. Schenk. "Die Bauchspeicheldrtise d. Embryo." Anatomisch-phy- 

 siolofjische Untersuchungen. 1872. 



(568) E. Selenka. "Beitrag zur Entwicklungsgeschichte d. Luftsa'cke d. Huhna." 

 Zeit. f. iviss. Zool. 1866. 



(569) L. Stieda. Untersuch. lib. d. Entwick. d. Glandula Thymus, Glandula 

 tlujroidea, u. Glandula carotica. Leipzig, 1881. 



(570) C. Fr. Wolff. "De formatione intestinorum." Nov. Comment. Akad. 

 Petrop. 1766. 



(571) A. Wolfler. Ueb. d. Entwick. u. d. Bau d. Schilddriise. Berlin, 1880. 

 Vide also Kolliker (298). Gotte (296), His (232 and 297), Foster and Balfour (295), 



Balfuur (292), Remak (302), Schenk (303), etc. 



Teeth. 



(572) T. H. Huxley. "On the enamel and dentine of teeth." Quart. J. of 

 Micros. Science, Vol. in. 1855. 



(573) R. Owen. Odontograplnj. London, 1840 1845. 



(574) Ch. S. Tomes. Manual of dental anatomy, human and comparative. London, 

 1876. 



(575) Ch. S. Tomes. "On the development of teeth." Quart. J. of Micros. 

 Science, Vol. xvi. 1876. 



(576) W. Waldeyer. "Structure and development of teeth." Strieker's His- 

 tology. 1870. 



Vide also Kolliker (298), Gegenbaur (294), Hertwig (306), etc. 



B. E. II. 41 



