2 58 THE SALAMANDER 



but they may be scraped off without leaving any apparent trace, and 

 while there may be some entry of lymph at these points it is very un- 

 likely in view of the free passage for this fluid into the veins by means 

 of the central lymph heart in the immediate vicinity. 



F. Lymphatics oj the Head (see also PL XIX, fig. 70). 



These may be conveniently distinguished as 'dorsal' or 'ventral* 

 according to their position relative to the mouth. 



The dorsal lymphatics oj the head (Fig. 70) are almost entirely con- 

 fined to a pair of Y-shaped sinuses beneath the eyes — the peri-orbital 

 sinuses (s.ly.p-o.). They were first described by Tretjakoff (1930). 

 Each sinus lies in the posterior half of the orbit, between the M. 

 levator bulbi and the skull, so that the bulbus oculi rests between the 

 limbs of the 'Y', while the stem passes across the palato-quadrate and 

 enters the peri-pharyngeal trunk. A small vessel from the peri- 

 orbital sinus passes through the antrum petrosum laterale and enters 

 the jugular sinus. 



As Tretjakoff points out, in Urodeles lymph has replaced blood 

 as a 'cushion' for the eye, enabling it to turn freely, since in fish that 

 function is performed by the peri-orbital blood sinus. 



Lymph capillaries are rich on the roof of the mouth and pharynx, 

 and they also ultimately join the truncus peri-pharyngeus. 



The ventral lymphatics 0} the head(¥\g. 68) are much more numer- 

 ous and extensive than the dorsal sinuses. On removing the skin 

 there may be seen, in addition to the subcutaneous network already 

 described, a lymphatic sinus running around the lower jaw — the 

 mandibular sinus (s.ly.man.). At the posterior margin of the M. inter- 

 mandibularis this sinus unites with the submaxillary network to 

 form a common stem that passes dorsalwards between the above- 

 named muscle and the M. interhyoideus and enters the sinus mandi- 

 bularis profundus. 



The sinus mandibularis profundus (s.ly.m.pf.) is a short sinus 

 situated mesial to the angle of the lower jaw. 



If the submaxillary network be removed, and the MM. inter- 

 hyoideus and intermandibularis cut along the linea alba and turned 

 back, the deeper sinuses may be traced. They probably arise from 

 the tongue as the central organ, although the whole floor of the 

 mouth and pharynx is rich in lymph capillaries. The lymphatics 

 of the tongue drain into a saccus copularis (sac. cop.), an irregular 

 sac lying on the dorsal side of the copula, and the lymph flows there- 

 from by several alternative routes. In injected specimens the saccus 

 copularis may be seen extending anteriorly from the copula as a small 



