DIGESTIVE TRACT OF THE CAT. 



studied with the greatest ease. To make such a dissection 

 of the older embryos is a comparatively simple affair, and 

 it is perfectly possible with the smaller ones, although some- 

 what more difficult. The method has the great advantage 

 of speed, but it is not an economical one, as now and then 

 an embryo is necessarily inadvertently sacrificed. In the 

 study of the younger stages, sections are indispensable, as 

 they are of great aid in the verification of a diagnosis. 



The microscopic drawings were made with the camera 

 lucida, and all the others are careful copies of the different 

 specimens. Fig. 1 represents a side view of the abdominal 

 and thoracic viscera of an embryo 34: mm. The body walls 

 have been removed, and all the organs are seen in sihi. 

 They present no difiiculty whatever in their identification. 

 Anteriorly, a coil of intestines is seen which was contained 

 within the cavity of the umbilical cord. In an embryo of 

 this length, one would not expect to find them in this posi- 

 tion, but as we shall see later, the date of their entrance into 

 the coelom proper is prone to great variation. 



Intestines Extra-Abdominal. 



For many years the fact has been recognized that at a 

 certain period in the development of the human embryo, 

 portions of the intestine lie outside of the abdominal cavity 

 proper, within the cavity of the umbilical cord, which at 

 this period is a direct continuation of the coelom. These 

 portions include the ileum, the Ccecum, a part of the colon, 

 and a large proportion of the jejunum. They remain for a 

 certain space of time in this position, and then enter the 

 abdominal cavity proper. It seems to me that until recently 

 the full importance and significance of this phenomenon has 

 not been appreciated, since it must necessarily have an im- 

 portant influence on the future position of the abdominal 

 viscera. 



The literature on this subject was very meagre before 

 the appearance of two articles by Mall, and it is to him that 



