Lhnbilic Hernia 1047 



the normal manner. In tracing the development of the embryo 

 on page 558, we noted that the somatopleur folds ventralwards 

 and finally unites upon the median line, to constitute the um- 

 bilicus, through which normally pass the allantoic stalk, in- 

 cluding the allantoic or umbilic arteries and veins, the urachus, 

 and the yolk stalk, surrounded by the amnion. 



During the earlier periods of fetal life, the abdominal cavity 

 is comparativel}' small, while the abdominal viscera are so volu- 

 minous that there is not sufficient room within the cavity to ac- 

 commodate them. They consequently press, or grow outward 

 through the wide umbilic ring into the navel cord, so that, in 

 fetuses of an early age, a large part of the intestinal mass, 

 omentum, and liver, may lie outside the abdominal cavity, lodged 

 in the umbilic cord. As the fetus develops and approaches ma- 

 turity, the abdominal cavity increases in size, while the umbilic 

 ring gradually contracts, until finally the opening becomes 

 virtually occluded and the margins of the ring adhere closely to 

 the umbilic vessels. For reasons unknown to us, the normal 

 closure of the umbilic ring may not occur, and when the young 

 animal is born there persists a variable-sized opening through 

 the abdominal floor, usually elongated from before to behind as 

 an oval .slit, wider at the anterior end. In some cases the open- 

 ing is almost circular in form. The diameter of the opening may 

 vary from so small a size as to be barely distinguishable, up to 

 six or eight inches. The resulting hernial sac corresponds in size. 



The defect may be present in any species of domestic animals, 

 though it attracts the most attention, and perhaps is most fre- 

 quent, in foals, pigs and puppies. 



Some writers recognize a congenital and acquired umbilic 

 hernia. Only the congenital defect is of interest to us. Some 

 writers have claimed that an acquired or accidental umbilic 

 hernia may be caused by severe muscular exertion of the new- 

 born animal, in running or plaj'ing, but we find no records of 

 cases in our literature to substantiate the correctness of such a 

 view, and have not observed such an occurrence in actual practice. 

 We have observed from time to time that umbilic herniae, which 

 were comparatively inconspicuous at the time of the birth of the 

 young animal, later became more conspicuous, and were in- 

 creased in size to such a degree as to attract attention. When 

 umbilic hernia exists at the time of the birth, anything which 



