INTESTINAL TRACT OF MAMMALS. 



219 



sj)iral ma}' be united either by their own primitive mesenteiy, 

 by the primitive mesenter}' of Meckel's tract, against which they 

 are fixed, or by adventitious fibres. There is, l)owever, a definite 

 morphological criterion. The pi-imitive mesentery of the loop 

 which is coiled into a spiral, whether it be retained in whole or 

 in part, fused with or replaced by the mesentery of Meckel's 

 loop or adventitious fibres, must have been attaclied along the 

 primitive dorsal line of the gut, that is to say, the side of the 

 hind-gut opposite to that on which the caecum lies, the side into 

 which the ileum opens. In text-fig. 19 I have dotted in the 

 j)rimitive mesenteiy, and it will be seen at once that in the figure 

 of Modoqua Dr. Beddard has adjudged the apex correctly (X), 



Text-fio-uie 19. 



Diagrams of Beddard's types of colic spirals. 



1. 3TadoqtM pMlHpsi. 



2. Traguhis stanleyanus. 



Modified from Heddard (1909, text-fig. 13, 1, 2). The distal end of the ileum, the 

 csecum, and the entering limb of the intestine in black; the outgoing limb is 

 unshaded. X. Beddani's apex, the true apex in 1. XX. The true apex in 2. 

 The dotted surface is the primitive mesentery of the loop. 



but that in the figure of Tragulus he has adjudged it incorrectly. 

 If in that ligure the point marked X were the apex, tlien the 

 mesentery would be attached to the wrong side of the gut. If, 

 on the other hand, the mesentery be considered, the point that I 

 have marked XX is seen to be the true apex, and the blackening 

 of the ingoing limb should have been continued from X to XX, 

 so abolishing the distinction between the two types. Preciselv 

 in the same way, in Dr. Beddard's figures of Cej^halophus maxiveUi 

 and Antilocapra americana (Beddard, 1909, text-fig. 13, 2a, 2h) 

 and in Dr. Lonnberg's figure of the Elk (Lonnberg, 1907, fig. 4), 

 from which Dr. Beddard's method was taken, tlie point tliat has 



