108 DEVELOPMENT OF THE SYSTEMIC LYMPHATIC VESSELS 



Such spaces (77) are seen in the two sections lateral to the 

 oesophagus. They apparently develop from the beginning as 

 intercellular clefts, without relation to embryonic veins. The 

 preazygos region presents these spaces in almost all 13 and 14 

 mm. embryos. Their development in the mammalian embryo is 

 of the utmost phylogenetic significance and affords important evi- 

 dence in the interpretation of systemic lymphatic ontogenesis in 

 the sauropsida, and especially in reptiles. The investigation of 

 avian and reptilian lymphatic development has been 'carried on 

 for the past year in the anatomical laboratory of Columbia Uni- 

 versity. These researches are now nearly completed, and some 

 of the main results were presented at the 27th session of the 

 American Association of Anatomists at Cornell University in 

 December of last year. They establish a common genetic ground 

 plan for the development and adult organization of the amniote 

 lymphatic system. The avian and reptilian type only differs 

 from that encountered in the mammal in respect to the higher 

 degree of development of the jugular lymph sac, as an anterior 

 or cervical veno-lymphatic heart, in the ontogenetic appearance 

 of other areas of equal phylogenetic significance, as remnants of the 

 multiple ancestral series of segmental veno-lymphatic hearts, 

 and in the preponderance of peripheral lymphatic development 

 by confluence of independent intercellular mesodermal spaces, 

 not associated topographically, as in the mammal, with tem- 

 porary embryonic venous channels. In other words, the extra- 

 intimal peri venous development of the majority of peripheral 

 lymphatic channels described in this communication appears 

 as a caenogenetic process in the mammalian embryo, whereas 

 in the sauropsid amniotes most of the systemic lymphatic 

 channels develop along more primitive phylogenetic lines, by the 

 direct confluence of numerous intercellular mesodermal spaces. 



These relative conditions have been outlined in a previous 

 publication on the phylogenetic relations of the lymphatic and 

 blood-vascular systems in vertebrates. 38 The results of the more 



38 Geo. S. Huntington, "The phylogenetic relations of the lymphatic and 

 blood-vascular systems in vertebrates." 



Anat. Record, vol. IV, no. 1, January 1910. . 



