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The Intracranial Vascular System of Sphenoolon. 

 By Arthur Dendy, F.E.S. 

 (Eeceived March 30,— Read April 22, 1909.) 

 (Abstract.) 



This memoir contains a detailed description, with illustrations, of the 

 intracranial blood-vessels of the Tuatara, of which no account has hitherto 

 been published. The description is believed to be more complete than any 

 hitherto given for any reptile, and a considerable number of vessels are 

 described which have not hitherto been noted in Lacertilia. This compara- 

 tive completeness of detail is largely due to the employment of a special 

 method of investigation. By this method the entire contents of the cranial 

 cavity are fixed and hardened in situ, and are then in excellent condition 

 either for dissection or for histological purposes. The brain does not occupy 

 nearly the whole of the cranial cavity, there being a very large subdural space 

 (especially above the brain), across which many of the blood-vessels run, 

 together with delicate strands of connective tissue which connect the dura 

 mater with the pia. The eyeballs are removed and an incision is made on 

 each side in the cartilaginous wall which separates the cranial cavity from the 

 orbit. Acetic bichromate of potash (made up according to the formula given 

 by Bolles Lee) is injected into the cranial cavity through these incisions, and 

 the entire animal, after opening the body cavity, is suspended in a large 

 volume of the same fluid for about five days, and then graded up to 70 per 

 cent, alcohol. When the cranial cavity is now opened up the cerebral vessels 

 are seen with extraordinary distinctness, although they have not been arti- 

 ficially injected. 



Further details were made out by means of serial sections, both transverse 

 and longitudinal, and both of the adult and of advanced embryos (Stage S). 

 In most respects the arrangement of the intracranial blood-vessels agrees 

 with that found in the Lacertilia, so far as these have been investigated, but 

 there is an important difference in the fact that the posterior cephalic 

 vein leaves the cranial cavity through the foramen jugulare and not 

 through the foramen magnum, while a slightly more primitive condition 

 is shown in the less complete union of the right and left halves of 

 the basilar artery. Sphenodon makes some approach to the condition 

 of the Chelonia in this latter respect, but differs conspicuously from 

 this group in the fact that the circle of Willis is not completed 

 anteriorly, as well as in the fact that no branch of the posterior cephalic 



