35 



the arterial canal of the larger branchia. The interior of this canal in both 

 branchiae presents a double series of orifices, leading to the branches which ex- 

 tend along the concave margins of the laminEe ; which branches subdividing as 

 the laminae subdivide, distribute the blood to all parts of this beautiful structure, 

 and ultimately terminate in the branchial vein (10. 10. pi. 5. & 6.). 



Of the muscularity of the part inclosing the brancliial artery there can be little 

 doubt ; such a power being equally required for the propulsion of the blood into 

 the smaller branches of the artery, and for the motions of the bi-anchial laminjE 

 themselves, which are indispensable in aquatic respiration. 



The branchial vein returns along the opposite side of the branchia ; its cavity 

 does not present a double series of separate orifices as in the artery, but a line 

 of alternate slits connected together like an alternately pinnate stem. After 

 quitting the roots of the branchiae, the veins cross over on the dorsal aspect of 

 their corresponding arteries, but without undergoing any dilatation as in the 

 Cuttle-fish, and enter the four corners of the systemic ventricle {t. pi. 5. & 6.), 

 where each is provided at its termination with a single semilunar valve (11. 11. 

 pi. 6.). This ventricle is transversely quadrate in form, and is eight hues in the 

 long, and four in the short diameter : its interior presents fleshy columns decus- 

 sating each other transversely. Two arteries arise from it ; one supei'ior, and 

 small (12. pi. 5. & 6.), whose orifice is furnished with a double valve; the 

 other inferior, and of large size (16. pi. 6.), coming off" near the left corner of 

 the ventricle, and accompanied, for the extent of five Unes, by a muscular struc- 

 ture (16'. pi. 6.) similar to the muscular bulb of the branchial artery of fish, at 

 the termination of which is a single valve (17. pi. 6.) In addition to these there 

 is a singular part connected, but not communicating with the ventricle ; it is an 

 elongated pyriform sac (18. pi. 5.), attached by a contracted origin near the root 

 of the large aorta, but soon dilating and acquiring a width of two lines, and then 

 gradually contracting and becoming connected by its other extremity to the 

 venous sinus above : its pai'ietes are membranous ; it contained a firm co- 

 agulated substance, but had no apparent outlet. Its position and connexions 

 would induce a belief that it had established, at some previous period of ex- 

 istence, a communication between the venous sinus and systemic ventricle, inde- 

 pendent of the branchial circulation . 



The lesser aorta runs fonv^ard a httle way, and gives off'a branch (13. pi. 5. & 6.) 



f2 



