The Anatomy of Chlamydoselachus 



463 



the greater part of its course" (Ayers, 1889, p. 195). Concerning the part of this vessel 

 which Ayers calls the cranial aorta, AlHs (1908, pp. 111-112) comments as follows: 



Ayers shows and describes, in Chlamydoselachus, a small median vessel, which runs 

 directly forward from the point where, according to his nomenclature, the dorsal aorta is 

 joined by the third pair of aortic roots; that is, in the nomenclature employed by me, from 

 the point where the lateral dorsal aortae unite to form a single median trunk. This vessel 



Text-figure 107. 



The dorsal aorta and its branches in Chlamydoselachus, ventral view. The myelonic 



(basilar) artery is displaced slightly to one side so as to be seen. 



ab, arteria basilaris; acp, a. cerebralis posterior; acr, a. centralis retinae; aom, a. ophthalmica magna; apsb, afferent 

 pseudobranchial artery; da, dorsal aorta; ea 2-3, efferent arteries of second and third branchial arches; ec, external 

 carotid artery; epsh, efferent pseudobranchial artery; ic, internal carotid artery; Ida, lateral dorsal aorta; fehy, 



posterior efferent hyal artery. 

 After Allis, 1923, Fig. 60, pi. XXIII. 



is said by Ayers to extend forward to the pituitary body, and it is called by him the cranial 

 aorta, that being the name given by Hyrtl to a similar vessel said to have been found by him 

 in Scyllium. This median vessel, described in these two fishes, has been discussed by both 

 Dohrn and Carazzi, and there seems some doubt as to its existence; or, if it exists, as to its 

 being an artery. I have accordingly not given any consideration to it in my diagrams. 



Further, Allis (1911, p. 516) states concerning the ''cranial aorta" of Chlamy- 

 doselachus: ''No trace whatever of such a vessel could be found in either of my two 

 specimens, notwithstanding that it was most carefully and particularly looked for." 



Since the discredited concept of a cephalic or cranial aorta existing as a median 

 unpaired structure is of some historical importance, I append a further consideration of 

 it by quoting the following from Corrington (1930, pp. 227-228): 



