THE VASCULAR SYSTEM 257 



becomes divided into two more or less distinct sections, namely, a 

 pars dorsalis lying between the nerves of the brachial plexus and the 

 scapula and forming the subscapular sinus proper, and a pars ven- 

 tralis which, although in frequent communication with the former 

 sinus, is separated from it by the nerves of the brachial plexus and 

 by the subclavian artery. Its anterior extremity lies ventral to the 

 aortic arches and is separated by them from the peri-pharyngeal trunk. 



The sinus subscapularis^ pars dorsalis (s.ly.sc") receives the T. 

 lymph, long, lateralis, a portion of the T. lymph, long, parepigas- 

 tricus, the post-axial trunk from the fore-limb and the transverse 

 trunk from the subvertebral stem already mentioned. Its lymph 

 flows into the pars ventralis by two main tracks, one, a direct path, 

 just anterior to the third spinal nerve, and the other by a circumflex 

 route, the T, lymph, circumflexus scapulae (t.ly.circ.sc), around the 

 lateral aspect of the scapula, between the bone and the MM. dorsalis 

 humeralis and dorsalis scapulae. This trunk receives the pre-axial 

 trunk from the limb just before joining the pars ventralis, and also 

 sends a branch directly forwards to enter the jugular sinus. 



The pars ventralis (s.ly.sc.') is a large sac-like structure closely 

 surrounding the roots of the main veins. In addition to the con- 

 nexions with the pars dorsalis, already mentioned, the pars ventralis 

 receives the remainder of the T. lymph, long, parepigastricus, i.e. 

 the portion entwining the anterior epigastric veins (t.ly.l.pe.) and also 

 2. sinus anastomoticus (s.ly.anas.) from the pars ventralis of the opposite 

 side. This sinus passes round through the fold between the peri- 

 cardium and the peritoneum, ventral to the oesophagus, and some- 

 what dorsal to the posterior end of the ventricle. Entering the pars 

 ventralis anteriorly are the sinus thyroideus (s.ly.th.), an elongated sac 

 lying lateral to the thyroid gland, and a communication with the 

 subcutaneous sinuses covering the M. interhyoideus posterior. The 

 latter connexion penetrates the muscle and passes a short distance 

 laterally over the dorsal side thereof before entering the pars ventralis. 



The pars ventralis, in turn, discharges into the truncus peri- 

 pharyngeus by means of several vessels that pass in mesialwards 

 between the aortic arches. 



Panizza supposed that the contents of this sinus flowed into the 

 subclavian vein, which is undoubtedly incorrect, although, in the larva, 

 Hoyer and Udziela show several fine connexions between it and the 

 ductus Cuvieri and the anterior cardinal. The appearance in the adult, 

 however, renders it extremely doubtful whether these communica- 

 tions persist. There are a number of fine lymph capillaries adhering 

 very firmly to the bases of the internal jugular and subclavian veins, 



4038 c 



