192 BULLETIN OF THE 



we have several species of sharks whose anatomy has been described by 

 Hyrtl, 8 Parker, 4 and others, such as Scyllium, Mustelus, Zygasna, etc. 

 Furthermore, it seemed to me that the accumulation of blood-vessels 

 about the hypophysis cerebri could be reasonably accounted for on the 

 •assumption that the vessel which Hyrtl 3 describes is in truth a remnant 

 of a much larger vessel of functional activity during embryonic life 

 only, which sustained such relations to the vascular structures about 

 the pituitary space as would lead us to search for the remains of 

 preoral aortic arches. His words are as follows (loc. cit., p. 5): "Bei 

 feinen Injectionen lasst sicht leicht erkennen, dass diese Aorta, welche 

 Kopfaorta genannt zu werden verdient, durch eine in die Mittellinie 

 des Schadel-basalknorpels nach vorn gehende Fortsetzung bis zur Ein- 

 trittsstelle der Carotis interna in die Schadelkapsel sich erstreckt. 

 Tab. I. Fig. 1, lit. i." Again the vessels called carotids by Hyrtl, 8,6 

 Muller, 6 and Parker, 4,7 seemed to complete the aortic circulation in 

 front by bringing blood from the ventral to the dorsal side of the di- 

 gestive tract, and were in a special sense the homologues of the carotids 

 of the Mammalia, of which more will be said further on. 



These conclusions were the outgrowth of my verification of Hyrtl' s 8 

 descriptions and figures of the arterial blood-vessels of the head in Scyl- 

 lium, Acanthias, and Mustelus. I did not at that time expect to be 

 able to verify my conclusions by the dissection of any living animal, 

 and consequently considered the views which form the essence of this 

 paper to be of little value because not demonstrable. The vascular sys- 

 tem of Chlamydoselachus proves the contrary, however, and under the 

 circumstances it is now a matter of no inconsiderable interest to find 

 out how the Notidanid sharks comport themselves with respect to the 

 cephalic arteries. 



I am not certain that Hyrtl has ever seen the "Kopfaorta" as it 

 exists in Chlamydoselachus, (i. e. imbedded in the cartilage of the basis 

 cranii,) for from his description of it quoted above it is not clear 

 whether the injected vessel figured in his plate runs in, i. e. through, the 

 basis cranii, or only in the middle line and ventrad of that structure. 



3 Hyrtl, Joseph. Die Kopfarterie der Haifische. Denkschrift. d. Wiener Akad., 

 XXXII., 1872. 



4 Parker, T. J. On the Blood-vessels of Mustelus antarcticus. Phil. Trans., 

 Vol. CLXXVIL, 1886. 



5 Das Arterielle Gefasssystem der Rochen. Wiener Sitzungsberichte, 1857. 



6 Muller, Johannes. Vergleichende Anatomie der Myxinoiden. Berlin, 1839-41. 



7 Parker, T. J. Zootomy, 1884. 



