3o6 Veterinary Obstetrics 



or eardrum. Rarely the hyomandibular gill-slit opens com- 

 pletely upon the exterior to constitute gill-slit fistula of the new 

 born. 



The embryonic line of demarcation between the stomatodeum 

 and fore-gut is not perfectly known in the adult, but is in the 

 immediate vicinity of the soft palate, the buccal mucosa and the 

 teeth being derived from the stomatodeal epiblast, the tongue 

 growing forward from the hypoblast of the floor of the fore-gut. 



Later in the life of the embryo, varying according to species, 

 there appears, opposite the posterior end of the hind-gut, a dis- 

 tinct depression in the epiblast, the proctodeal pit. The invagi- 

 nation of this pit is of a similar character to that of the stomato- 

 deum and soon extends sufficiently toward the hind-gut that 

 only a thin membrane remains between them, consisting exter- 

 nally of a layer of epiblast and internally of hypoblast. Nor- 

 mally, this pit soon opens into the hind-gut and the alimentary 

 canal now communicates with the exterior, both anteriorly and 

 posteriorly. 



Various aberrations in the development of these parts occur. 

 The most common is an arrest in the development of the hind- 

 gut, by which a portion of it is wanting and it consequently does 

 not become connected with the proctodeal pit and does not open 

 exteriorly. In such cases, the young animal is born devoid of 

 a rectum. In other cases, the membrane between the proctodeal 

 pit and the hind-gut fails to disappear and the young animal is 

 born without an anus, as shown in Fig. 42. In still other in- 

 stances, as recorded by Gurlt, the intestine ceases at the vitelline 

 stalk, passing out through the umbilicus, where it ends blindly. 



A highly interesting aberration involving the digestive tract, 

 and spinal column, is that recorded by Gurlt and illustrated 

 in Fig. 38, which he designates as Schistocormus fissi-dorsiialis 

 siibecostatus and describes as a cleft in the dorsal wall of the body, 

 beneath the spinal column on the left side, through which the 

 .stomachs and other abdominal viscera prolapse. 



Gurlt remarks that the aberration is very rare, he having 

 known of three instances, one in the calf, two in lambs — all in 

 ruminants. 



We have ob.served a single case, resembling that of Gurlt in 

 many respects but .showing important differences. "Figs. 39 and 

 40 delineate briefly its character. In this instance, the omasum, 



