The Origin and Development of the Lymphatic System. 59 



of the process in the living chick. He notes thai the striated muscle 

 of the heart comes from the myotomes. Huntington (57) states that 

 in the reptiles there are jugular lymph sacs like those of mammals. 

 The lymph vessels of reptiles he describes as arising from tissue spaces. 



V. PERIPHERAL LYMPHATIC SYSTEM. 



1. In the Pig. 



A. i - 1 :< > \r Til i: .i dgtjlak i.vm rn sacs. 



I shall again base the description of the peripheral lymphatics on 

 the vessels in the pig, since more of the main trunks have been worked 

 out in that form than in any other. The description is taken from 

 the work of A. II. Clark CM). "I' Heuer ( 13) and myself. 



The development of the jugular sac in the pig has already been given 

 in section 1 \'. A study of the distribution of the lymphatic vessels 

 from thi' jugular sac mu«1 he based mi the form of the jugular sac 

 as seen in li.u's. ] and 8. In fig. 1 there is a. primary sac between the 

 internal and external jugular veins and a complete arch of lymphatic 

 capillaries extending into the dorsal lymphatic area. This entire 

 plexus becomes transformed into the sac, so'that, as shown in Bg. 8, 

 the sac consists of a stein along the internal jugular vein ami a com- 

 plete dorsal arch. Through following the fate of this sac A. II. Clark 

 divides it into three parts, the sac stalk: the anterior curvature along 

 tin' internal jugular vein ; and the apex, in the posterior triangle of the 



heck. 



The sac -talk becomes the deep jugular lymphatic trunk. It is 

 usually uiie large vessel, hut may give oil' lymphatics which run direct I \ 

 in the pharynx. The anterior curvature becomes a lymph gland and 

 it sends vessels to the pharynx and Eustachian tube and to the nose. 



The apex of the sac. as is seen in fig. 8, becomes the largest part 

 of the jugular sac. This part lies in the posterior triangle of the 

 neck ami develops in the pig into one gland, the largest in the 

 neck (Clark 24). This corresponds to the group of -'lands in the pos- 

 terior triangle of the neck particularly well shown in Bartels (I'M 

 fig. ;!() from new horn child. 



The tact thai the jugular lymph sac in the pig develops into two 

 lymph glands ami the deep jugular lymphatic trunk is well brought 



