GENERAL ANATOMY OF EMBRYO OF 12 MM. 



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Oe, Tra 



FIG.- 180. PIG EMBRYO OF 12.0 MM. RECONSTRUCTION FROM THE TRANSVERSE SECTIONS, SERIES 5. 



The embryo has been drawn as if transparent, to show the form of its pharynx and the relations of the pharyngeal 

 gill-pouches to the grooves on the outer surface of the embryo. Cbl, Cerebellum. C.S, Cervical sinus. Dien, 

 Diencephalon. ep.b, Epibranchial body. H, Cerebral hemisphere. Hy, Hypophysis, which arises as an 

 evagination from the oral cavity. Inf, Infundibular gland, which arises as a median evagination from the 

 floor of the fore-brain, l.gr, Lachrymal grooVe. m, Maxillary process. M.b, Mid-brain. Mdb, Mandibular 

 process. Md.ob, Medulla oblongata. na.ex, External nasal opening; the nasal cavity is dotted, na.pl, Nasal 

 plate separating the nasal pit from the oral cavity; by the rupture of this plate the inlernal nares is formed 

 later, ni, Internal nares. nod, Nodulus thymicus. Oe, (Esophagus. Op, Eye. Ot, Otocyst. Sp.c, S] . >a! 

 cord. Th, Median thyroid gland, thym, Anlage of the thymus (part of the third gill-pouch). Tra, 

 Trachea. Yen. IV, Fourth ventricle, i, Entodermal pouch of the first branchial cleft, the anlage of 

 the Eustachian tube and tympanum. 2, Entodermal pouch of the second gill-cleft; it actually opens to the 

 exterior. 3, Entodermal pouch of the third branchial cleft. 4, Entodermal pouch of the fourth gill-cleft, 

 the lower fork of which is the anlage of the lateral thyroid. X 20 diams. (Drawn byF. T.Lewis.} 



