The Anatomy of Chlamydoselachus 



439 



mesonephroi. Anteriorly, the left urinary sinus gradually diminishes in caliber as it 

 extends within the dorsal mesentery close to the uteri which are united by their medial 

 walls for a distance of 40 mm. in front of the urogenital sinus. At 75 mm. from the 

 urogenital orifice, the left urinary sinus tapers rather abruptly to become continuous with 

 the left mesonephric duct which extends forward in the dorsal mesentery. The right 

 urinary sinus is apparently cystic, and was found by dissection. It begins as far poste- 

 riorly as the left urinary sinus, but is only 60 mm. long and 8 mm. wide in its widest 

 portion. Its relations to the wall of the urogenital sinus and to the dorsal mesentery are 



Text'figure 91. 

 Urinary sinuses (ventral views, three- 

 fifths natural size) of three female 

 specimens of Chlamydoselachus: A, 

 specimen No. Ill; B, No. I; C, No. II. 

 In order to show the correct propor- 

 tions, the outlines are drawn as if the 

 sinuses were spread in a horizontal 

 plane. 



Drawn from specimens in the American 

 Museum of Natural History. 



similar to those of the left urinary sinus. While the left urinary sinus readily admits 

 a probe by way of the urethral pore, and the probe continues into the left mesonephric 

 duct, no opening for the right urinary sinus could be found in any direction. 



Specimen No. I has a pair of well-developed urinary sinuses (Text-figure 91b) 

 situated close to the median plane but lacking any direct communication with each other. 

 In this specimen the two uteri are united by their medial walls for a distance of 50 mm. 

 in front of the urinary sinuses, hence are supported, in this region, directly by the 

 dorsal mesentery. The relations of the urinary sinuses to the wall of the urogenital 

 sinus and to the dorsal mesentery are the same as in specimen No. Ill, save that here the 

 urinary sinus of the right side is confined to the dorsal mesentery. Each urinary sinus 

 connects posteriorly with its short urethral pore, through which it may be probed. The 

 urinary sinus of the left side is larger than the corresponding sinus of No. Ill; it is about 

 90 mm. long, and 10 mm. wide throughout more than half its length. The posterior end 

 narrows abruptly, the anterior end so gradually that its Hmit must be determined some- 

 what arbitrarily. The sinus is continuous anteriorly with the left mesonephric duct 

 which was probed more easily than that of No. III. The right urinary sinus is sHghtly 

 smaller than the left. It is 85 mm. long, and 8 mm. wide throughout its middle third; 



