40 



MORPHOLOGY OF THE 



lobe presents in each a very different appearance. In the 

 17| mm. embryo it is comparatively insignificant. On the 

 other hand, in the embryo of 61 mm., it is very large and 

 prominent. Its outer edge is much thicker than its inner 

 edge, in consequence of which it forms an inclined plane, 

 sloping to the left, upon which rests the duodenum and its 

 mesentery. 



This lobe in the 111 mm. embryo and in the adult do 

 not differ materially from each other. 



In the ()1 mm. embryo the ascending colon was unformed, 

 but the transverse was fully developed. The caecum, in its 

 growth from left to right, rested upon the mesentery of the 

 duodenum which lay upon the caudate lobe. It is clear that 

 the ca3cum in its growth was forced to ascend this inclined 

 plane until it reached the duodenum, and then these struc- 

 tures, together with the overhanging edges of the right 

 central and caudate lobes, forced the caecum to change the 

 direction of its growth. 



Hence the caudate and right central lobes play an active 

 part in the limitation of the transverse and in the forma- 

 tion of the ascending colon. 



In the 17| mm. embryo the extent of protrusion of the 

 Spigelian lobe is very limited, and as has already been stated, 

 its apex was not far from the lesser curvature of the stom- 

 ach. This is quite different in the 61 mm. embryo. Here 

 this lobe is most prominent, and as we have already seen, 

 it gives the stomach great support. It is far less conspicu- 

 ous both in the embryo of 111 mm. and in the adult than in 

 the embryo of 61 mm. This is not due to an atrophy of the 

 lobe, but to an increase in the growth of both stomach and 

 liver, so that the proportions are entirely changed. 



A glance at the oesophageal groove in the different draw- 

 ings, shows a gradual change from the median line toward 

 the left. The change is most marked on comparing the 

 embryo of 1T| mm. with the embryo of 61 mm. This 

 corresponds to the period when the Spigelian lobe is most 

 prominent. The deep groove on its surface is seen with great 



