////: 



919 



diirin.u' youth, uml its definitive volumo is not acquired until the period of 

 puU-i ty. 



The thy m tut ;//;<,/ appears as a process of the respiratory mucous mem- 

 brane; it seem-; t<> l.e tunned at the 



larynx, and !_ r radiially descends along '<;. 



the trachea to the entrance of the 

 thorax. 



FIRST APPEARANCE OF THK I.L'XOS ; 



In a Fowl at four days ; b, At six days ; c, 

 Termination of bronchus in a very young 



HKVKI.olMK.vi OF THE DIGK8TIVK 

 APPAUATUS. 



In this paragraph, the develop- 

 ment of the alimentary canal will be 

 tirst studied, then that of the organs 

 annexed to it. 



A. ALIMESTAKY CANAL. We have 

 how the embryo, in becoming 



inenrvated, divides the blastodermic vesicle into two parts which com- 

 municate by a large pedicle. The external portion is the umbilical vesicle ; 

 the pedicle is the ouiphalo-mesenteric duct, and the inner part the intestinal 

 cavity. 



The latter may be decomposed into three portions : the anterior intestine, 



Fig. 447. 



EMDKVO OK IX*. , TW|.MV-II\I. |..VV> A11IK IA-I . HT I. V I Iil.N. 



nil .in -In-., t'nrmini; tli' I..W.T j:iw ; ( /, -/, 



! vi-c-.-i-al iircii.', ; ., l;i k 'lit :mri. !;/, '-''I't aurici.'; ./. Kijjht ventrirle; 

 A, I.cl't vi-ntrii I.-; i. Aortic bulb; A, A, Liv.-r, l.vt \MTII tin- t\w. lobes of whi<-li is 



iliviiii-il nrili' r Mi'tln- jili.ilo-n . .11: /, StmiiMch ; HI, Intc-tin.-, 



i-ii!iiiiiiiiiir;itint( with the uuibilir.ii ' i|ni Wolliiana; p, Al- 



l.intoj.-,; if, ,/, Aiit.-n..r cxt n-mitio ; /', . \tivinitie>. 



which f..rms the pharynx and oesophagus; tho posterior intettine, that gives 

 '' the rectum; and the middle intthtine, which 1> comes the stomach 

 and intestines. 



