RELATION OF LYMPHATIC TO BLOOD-VASCULAR SYSTEM 37 



The prevalent lack of cooixlinate deduction between verte- 

 brate morphology and palaeontology is accentuated bj^ contrast 

 with such publications as Weber's ''Saugethiere" and, more 

 recently, W. K. Gregory's "The Orders of Mammals", based 

 largel}^ on the author's joint work with Osborn, and on the latter 's 

 previous classical researches, and published bj^ the American 

 Museum of Natural History (Bulletin, vol. 27, February, 1910). 



Workers in the general field of vertebrate structure appreciate 

 fully the immense practical value in their own special investi- 

 gations of books of this type, in which, to quote Gregory's words, 

 "the data of systematic mammology, of comparative anatomy 

 and embrj'olog}" shall ultimately be integrated with the data of pal- 

 aeontology, to the great advantage of these now more or less 

 independent lines of study." 



In embryo 258 (fig. 21) the space ventral to the cardinal col- 

 lateral veins and the ascending lumbar lymphatic trunks, is oc- 

 cupied by a plexus of mesenteric lymphatics {51) draining into 

 the latter. On each side are seen sections of the ureter {58), and 

 further laterad of the iliac vessels {61). Ventral of the intestine 

 {62) are the Wolffian ducts {6Ji} and the cloaca {63), with the 

 hypogastric arteries {66) laterally. 



Fig. 21 shows the important central vascular region of the same 

 section in a magnification of 150 diameters. The relation of the 

 cardinal collateral trunks {74) to the ascending lumbar lymphatics 

 {75), and of the latter to the postcardinal veins {67, 68) can be 

 more clearly seen. The lumen of the mesenteric lymphatics 

 {51) still contains in places remnants of the decadent venous 

 plexus around and upon which they developed as replacing ex- 

 traintimal spaces. 



The three succeeding sections, tracing the structures caudo- 

 eephalad, are shown in figs. 22, 23 and 24, all in a magnification 

 of 150 diameters. The connections of the lymphatic channels 

 developing along the iliac vessels with the ascending lumbar 

 trunks are especially well seen on the left side of the three figures, 

 also the anastomoses between the two cardinal collateral veins in 

 figs. 23 and 24. 



Figs. 25 and 26 show transverse sections of the hinder end of the 

 body in a 20 mm. embiyo (series 241). 



