94 



ALLEN 



the branchial trunks were always filled with red corpuscles, and 

 unquestionably terminated in and apparently formed the prin- 

 cipal supply for the so-called inferior jugular vein. 



II. DISTRIBUTION OF THE SUBCUTANEOUS VESSELS IN 

 POLYODON. 



The distribution of the subcutaneous vessels in the head region 

 of Polyodoti, which is a cartilaginous Ganoid, and Lepisosteus, 

 a bony Ganoid, admits of so little comparison, that it seems 

 advisable to consider this system of vessels separately in each 

 case, rather than to take them up together in a comparative way. 

 In the former these vessels, in some respects, agree more closely 

 with the Selachians, while in the latter they are more like the 

 Teleosts. 



I. Cephalic Sinuses and their Connections. 



What has been designated as the cephalic sinuses (Fig. i, 

 Ceph.S.) in Polyodon are two rectangular-shaped reservoirs, 

 which are symmetrically placed on either side of the body, 

 directly mesad of the supra-clavicles, and only a little below 

 the level of the post-temporals. In the specimen from which 

 Fig. I was drawn their dimensions were about 40 by 18 mm. 

 With the exception of the posterior-ventral corner, each corner 

 of a cephalic sinus has an orifice. The trunk leading into the 

 posterior dorsal opening is the lateral ly?nphatic trunk (Fig. i, 

 L.L.T.). In the thoracic region the lateral trunks were the 

 only subcutaneous vessels found ; though both dorsal and ven- 

 tral trunks were observed farther caudad. Very singular in 

 Polyodon the lateral trunks have an extremely small diameter, 

 but little, if any, greater than the lateral line canals. Fortu- 

 nately, however, they increase in caliber upon approaching the 

 cephalic sinuses ; otherwise it would be impossible to inject 

 them, except with a very fine hypodermic needle. What are 

 represented as the cephalic lymphatic trunks (Fig. i, Ceph.L. 

 T.) terminate in the anterior dorsal corners of these sinuses, and 

 in one way or another these great canals drain the entire head 

 region. The openings from the anterior ventral corners lead 

 into papillas (Fig. i, V), which discharge themselves ventrad 

 into the jugulars ; either at the angles of their great bends in 

 front of the pectoral arches, or a little below. 



