The Anatomy of Chlaynydosdachus All- 



in studying the blood'vascular system of the gills of Chlamydosdachus, one is 

 impressed by the enormous increase in the cross'sectional area of the blood stream as it 

 leaves the gill'arch, as it enters the filaments, and again as it reaches the plexus of capil' 

 laries in the lamellae. There is a corresponding decrease as the blood returns to the main 

 efferent branchial arteries. The total arrangement functions to reduce the velocity of 

 the blood as it passes through a multitude of tiny capillaries. 



In the section on the respiratory system I have pointed out that in proportion to 

 body sizie the respiratory surface in Chlamydosdadius is very large — perhaps larger than 

 in most sharks. It seems likely that in fishes that live in the deeper waters of the ocean, 

 where it is always cold and where oxygen is not so plentiful as at the surface, there 

 is need for more efficient organs of respiration; but adequate data for comparison are 

 not available. 



In his well'organized treatise on the anterior arteries of sharks, Corrington (1930) 

 gives a refreshingly clear presentation of the essential data, illuminated by discussions 

 of its significance from a comparative point of view. His synonymy for these arteries 

 will be found very useful. Some remarks by Corrington (p. 205) on the hypobranchial 

 system of arteries will perhaps explain why I have not included a comparison of these 

 vessels in ChlamyAosdachus with those of the same region in other sharks : 



These [hypobranchial arteries] are the last arteries of the head to be formed before 

 assumption of the adult condition. This lateness of development and also absence in lower 

 groups argue that this system was one of the last vascular acquisitions of the immediate 

 shark ancestor. Increased bulk and muscular specialization of the subpharyngeal, inter- 

 branchial area demanded an extra mechanism for nutritive supply, and this was hence derived 

 from the nearest source. No homologies involving the alteration of any elements previously 

 present are necessary or possible, and none have been suggested as far as I am aware. . . . 

 There is no type arrangement for these arteries in either the Class or Order, or even in various 

 species, so that description must be of a somewhat general nature. 



The most elaborate figures of the arteries of the head of Chlamydosdadius are those 

 of Allis (1923). These (which are in color) should be consulted by any one wishing a more 

 comprehensive account than is given here. 



THE VEINS 



Very little work has been done on the venous system of Chlainydosdadius. Ayers 

 (1889) states that extensive venous sinuses, always simple in character, are developed 

 in the course of the large venous trunks. Portions of the principal venous trunks are 

 shown in Text'figure 105, copied from Ayers. These vessels are the internal jugular 

 vein iS.j.v), the cardinal vein (c.v.), the hepatic vein {h.v), and the tropeic or lateral 

 abdominal vein (tr.). The cardinal sinus (c.5.) seems unusually large, as in my own speci' 

 mens. The marked development of the venous sinuses is regarded by Ayers as a primitive 

 character. 



