DISTRIBUTION OF SUBCUTANEOUS VESSELS IN GANOIDS 97 



found in the hyo-opercularis fork of the cephalic trunk, at its 

 junction with the ventral fork, which opens towards the cephalic 

 sinus, but from its size one would not expect it capable of en- 

 tirely closing the opening. A little posterior to the division of 

 the cephalic canal a combined trunk formed from the fusion of 

 the last three branchial lymphatic vessels (Fig. i, X) is received 

 from below, which will be described in detail later on under the 

 head of the branchial lymphatic trunks. 



What is termed the -pericardial lymphatic trunk (Fig. i, 

 Per.L. T.) corresponds somewhat in position to the pericardial 

 sinus of Lepisostetis and the Teleosts, without presenting any- 

 thing like a sinus-like appearance. It is simply a canal running 

 along in front of the pectoral arch in the connective tissue that 

 surrounds the precava. Immediately after crossing the commu- 

 nicating vessel of the cephalic sinus with the jugular it makes a 

 dorsal curve to culminate in the cephalic trunk, near its union 

 with the cephalic sinus. 



In several different specimens of Polyodon blood was removed 

 with a pipette from the jugular and injected into a vial contain- 

 ing alcohol ; likewise some fluid from the cephalic lymphatic 

 trunk was placed in a second vial containing alcohol. Upon 

 settling, the corpuscles from the vein had a distinct brown or 

 reddish color ; while those from the cephalic trunk were prac- 

 tically colorless. Microscopic sections of the two trunks reveal 

 the walls to be structurally about the same. (Compare Fig. 

 22 with 23.) Both are composed mainly of fibrous connective 

 tissue, with scattering smooth muscle fibers, and both have nu- 

 merous papilla (P), which extend some little distance into the 

 trunk and may to some extent function as valves. The greatest 

 difference between these two vessels is in relation to their con- 

 tents. The cephalic canal is filled with leucocytes and a few 

 scattering red corpuscles, while in the jugular the red corpuscles 

 greatly predominate ; there being, however, in the latter a greater 

 proportion of white corpuscles than would be found in the mes- 

 enteric or inferior jugular veins. With the cephalic trunk in 

 the region covered by the field of Fig. 22 the red corpuscles 

 were to the white as 8 is to 153 ; while with the jugular in the 

 area covered by Fig. 23 the ratio of red to white was 36 to 



