THE HEART OF THE PORPOISE. 347 



places this in communication with the dilated commencement 

 of the duodenum, which has sometimes been regarded as a 

 fourth stomach. Its lining membrane presents longitudinal 

 rugJB continuous with those of the duodenum itself. The con- 

 joined pancreatic and biliary ducts open just beyond the di- 

 lated part of the duodenum. There is no ccecum, or demar- 

 cation between the large and small intestines. The bilobed 

 liver has no 2:all-bladder. 



In the heart the fossa ovalis is distinct, but there is neither 

 Eustachian nor Thebesian valve. The vena cava inferior is 

 long and wide, but is not especially dilated near the heart. 

 Muscular fibres are not continued on to it from the diaphragm.. 

 The aorta and pulmonar}'^ arteries are not dilated at their ori- 

 gins. The arteries have a great tendency to break up into 

 plexuses. Thus the internal carotids form great net-w^orks 

 which communicate with vertebral jDlexuses, extending through- 

 out the entire spinal canal. The brachial artery divides into 

 two branches, and these subdivide into innumerable parallel 

 twiffs. The intercostal arteries are the chief source of the 

 large thoracic plexuses, which lie at the sides of the vertebral 

 column in the dorsal half of the thorax. Finally, an arterial 

 rete mirahile surrounds the caudal aorta. Th(3 veins form 

 plexuses corresponding to, and mixed up with, those of the 

 arteries ; and a very large venous plexus lies on the subverte- 

 bral muscles in the abdomen and thorax. 



The respiratory apparatus of the Porpoise presents many 

 remarkable peculiarities. The contour of the front part of the 

 head, as bounded by the integument, is very convex — the cor- 

 responding facial region of the skull, on the contrary, is very 

 concave. The interval between the two is occupied, in part, 

 by fibrous and fatty tissue ; and, in part, by a singularly sac- 

 culated spiraciilar chamber, which connects the single spiracle 

 with the double external nares of the skull. Two valves, an 

 anterior and a posterior, lie immediately above these external 

 nares and close the communication between them and the 

 chamber, except at such times as it is forced open from below. 

 Each nasal passage remains distinct from the otlier as far as 

 the valves, the middle of each of the latter being fastened to 

 the septum, so that there may be said to be a pair of valves 

 for each opening between the passages and the spiracular 

 chamber. Each nasal passage, after it ceases to be surrounded 

 by bone, sends off two diverticula, one forward and one back- 

 ward. The anterior, which lies between the anterior valve 

 and the premaxilla, is a simple sac, lined with a thin, black, 



