484 



the efferent hyoidean and first branchial arteries and that, having 

 traversed a foramen in the ventral edge of the hind end of the skull, 

 falls into the lateral dorsal aorta. In Heptanchus no trace of this 

 small vessel could be found, but there is a small foramen that per- 

 forates the latero-ventral edge of the hind end of the skull, in a place 

 corresponding closely to that of the foramen traversed by the vessel 

 in Chlamydoselachus. No nervous or other structure could be found 

 traversing this foramen, but, as the foramen is found, it is of course 

 possible that a small artery may have traversed it in early stages and 

 have wholly aborted in the adult. Slightly posterior to this foramen 

 a delicate vertebral artery has its origin, on either side, from the 

 median dorsal aorta. This condition, in Heptanchus, naturally again 

 raises the question as to whether the little vessel in Chlamydoselachus 

 is the true dorsal end of the efferent hyoidean artery, and not simply 

 a specially developed vertebral artery that has exceptionally and 

 secondarily acquired a connection with the hyoideo-glossopharyngeus 

 dorsal commissure; and I have had the vessel again examined in 

 another specimen of Chlamydoselachus. 



In this specimen of Chlamydoselachus, as in the two examined 

 in connection with my earlier work, the little vessel in question has 

 its origin from the dorsal commissure that connects the posterior 

 hyoidean and anterior glossopharyngeus efferent arteries, and running 

 dorso-antero-mesially, gives off one small branch and then falls into 

 the lateral dorsal aorta. This small branch of the little vessel is 

 found on both sides of the head of my specimen and, going directly 

 to the nervus glossopharyngeus, can be traced for a short distance 

 proximally along that nerve. It does not apparently extend into 

 the cranial cavity, along with the nerve, but it is so delicate a vessel 

 that this could not be definitely determined in my uninjected specimen. 

 This branch was also found in the one specimen here examined in 

 connection with my earlier work, and its point of origin from the main 

 vessel is indicated in the figure illustrating that work. It was however 

 so delicate a branch that it was not considered of importance and so 

 was not traced, or even mentioned in the text. The fact, however, 

 that it runs proximally along a nerve may be of importance, as giving 

 to it a vertebral character. Posterior to the little vessel itself, another 

 and much smaller artery has its origin from the lateral dorsal aorta, 

 and traversing the projecting ventro-lateral edge of the chondro- 

 cranium goes to tissues in the region of the nervus vagus, this artery 



