The Anatomy of Chlamydoselachus 457 



In specimen No. IV (Text'figure 100b) the common aperture (c.) of the pericardio' 

 peritoneal canal is situated as in No. Ill, a few millimeters from the dorsal border of the 

 posterior pericardial wall. This opening has about the same size (12 mm. wide) as the 

 corresponding openings in the other specimens; but it is bordered laterally by thin lips 

 due to an extension of the pericardio'peritoneal sac {p. p. s.) which is about 22 mm. wide 

 though no deeper than in the other specimens. The openings into the paired canals 

 are smaller, and the canals are more slender. Each canal is about 13 mm. long and ends 

 in contact with the esophagus at the extreme anterior end of the peritoneal cavity. Both 

 canals end blindly. 



In two respects the pericardio'peritoneal canals of Chlamydoselachus differ from the 

 condition typical for elasmobranchs : the anterior unpaired portion is extremely short 

 and broad, forming a shallow sac; and the paired canals often end blindly. Of the eight 

 canals in my four specimens, five are closed at their posterior ends. It is noteworthy 

 that the closed canals are usually smaller than the open ones. It is apparent that there 

 is a tendency toward obliteration of the canals, and this may be interpreted as a depar' 

 ture from primitive conditions. 



BLOOD' VASCULAR SYSTEM 



Studies of the blood'vascular system of Chlamydoselachus have been almost entirely 

 limited to (1) the heart; (2) the arteries anterior to the heart; (3) the large venous trunks; 

 and (4) the venous sinuses of the claspers. These comprise, however, the most interesting 

 and complex portions of this system. In my own material, only a few portions of the 

 blood'vascular system are in a condition favorable for investigation. I have therefore 

 studied only the heart and the blood vessels of the gills. 



THE HEART 



Since there is much variation in the names that have been applied, by different 

 authors, to the anterior division of the elasmobranch heart, it is desirable to justify my 

 choice of the term conus arteriosus, which is used throughout this section. The present 

 status of our knowledge of the homologies of this portion of the heart is set forth by 

 Goodrich (1930, p. 538) in the following words: 



There has been considerable confusion in the nomenclature of the anterior region of the 

 heart. Bulbus cordis is the name now generally applied by embryologists to the anterior 

 chamber. But the name conus arteriosus, introduced by Gegenbaur to designate the anterior 

 muscular region of the Selachian heart, is often given to it. Moreover, the Selachian conus 

 does not [precisely?] correspond to that part of the heart so called in human anatomy. It 

 is best, then, to apply the name bulbus cordis, introduced by A. Langer, to the embryonic 

 structure throughout the Craniata, and keep the name conus arteriosus for the adult muscular 

 contractile chamber derived from it in Pisces and Amphibia. 



Carman's figures of the heart of Chlamydoselachus are reproduced as my Text'figures 

 101a and 101b. Of his specimen Carman (1885.2, pp. 18 and 19) writes : 



