DEVELOPMENT OF THE CHICK SECOND PERIOD. 323 



(fig. 343, A, under //), and the mucous layer being thus bent 

 inwards in a canalicular manner, forms the intestinal cleft 

 an open canal in communication with the yolk, running for- 

 wards funnel-shaped, towards the faucial cavity, and backwards 

 in the same manner to the rectum. At the beginning of the 

 fourth day the intestinal cleft has contracted, and exhibits but 

 a very small opening, which, extending soon after into a canal 

 or sac (fig. 341, k, I), passes over the peripheral mucous layer 

 as the intestinal canal (fig. 343, B, n), and throws itself com- 

 pletely around the yolk. The oral and faucial cavity gapes 

 widely, and extends into a narrower part or canal, the esopha- 

 gus, from which, inferiorly and posteriorly, a diverticular sac- 

 culus sprouts (fig. 343, B, z), the first rudimentary appearance 

 of the lungs ; a little farther on, an elongated enlargement of 

 the intestine is perceived, which indicates the situation of the 

 future stomach (fig. 343, k) ; the intestine then expands, and 

 goes off funnel-shaped towards the yolk (fig. 343, n, and in a 

 later form, fig. 341, k, /), and in like manner towards the rec- 

 tum, which still terminates in a blind sac ; the limits between 

 the small and large intestines are indicated by the evolution of 

 a couple of diverticula the capita cceca towards the end of 

 the third day. About the middle of the third day various 

 other parts are indicated in connection with the intestinal 

 canal, which enlarges in the places where these are to appear, 

 and sprouts out towards or into the vascular layer ; thus, two 

 little hollow offsets show themselves as the rudiments of the 

 liver, in which a venous net-work by and by appears, that re- 

 solves itself into the portal system. At the beginning of the 

 fourth day the two lobes of the liver appear as lappets of some 

 breadth (fig. 341, i), in which the composition, by means of an 

 aggregation of blind sacs, is apparent somewhat later ; another 

 small offset, or bunch, also shows itself in the vascular layer, 

 between the lobes of the liver ; this is the rudimentary pan- 

 creas; it grows slowly, but, on the fifth day, when the convo- 

 lutions of the small intestine begin to be formed, it has enlarged 

 considerably : at this time the spleen also makes its appear- 

 ance as a small red body. The pulmonic sac divides, and be- 

 comes more distinct, from the esophagus appearing first 

 pinched off from that part, and then provided with a pedicle 

 the future trachea ; on the fifth or sixth day the lung of the 

 one side is completely distinct from that of the other, and each 



