Formation of the Digestive Apparatits 2)^'j 



M, and the spleen, S, are protruding from a crater-like open- 

 ing in the head, through the occiput. The rumen and reticu- 

 lum are wanting in the specimen, fragmentary shreds indicating 

 that the}^ had been torn away accidentally or eaten away by 

 some animal before the specimen came into our hands. In this 

 case, the prolapse of the alimentary tract is not lateral, but dor- 

 sal, immediately upon the median line, obliterating for a distance 

 the cerebro-spinal axis. 



Fig. 39. ScHisTocoRMus Fissidorsualis. 

 Showing crater-like opening in the occipital region. 



Since the notochord becomes established prior to the formation 

 of the gut, it would seem improbable that the prolapse would 

 occur through that organ, but rather that it would pass in front 

 of it, and this is apparently what has occurred. A study of Fig. 

 41, /A^and PT, shows that, just anterior to the end of the noto- 

 chord, there is an infundibulum growing down from the thala- 

 mencephalon, or midbrain, while, just opposite, growing upward 

 from the posterior border of the stomatodeum, is the pituitary 

 pouch, which later becomes the pituitary body, the two infundi- 

 buli coming into immediate contact with each other. The 

 fore gut has pushed forward and upward, to escape through 

 this area of low resistance, upon the back of the head. The 

 fore-gut escaping, no neck has developed, and the sternum, ST, 

 extends forward beneath the pharynx, P, and the basi 

 occipital bone, BS. The illustration from Gurlt likewise indi- 

 cates a virtual absence of neck, though less pronounced. 



At first the alimentary canal is of the same length as the body 

 and forms immediately beneath the notochord, but later it in- 



