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Show 60 MR. F. E. BEDDARD ON THE ENCEPHALIC [May 16, § Brain of Iguana tuberculata. The plan of the cerebral arteries in this Lizard differs in a number of particulars from that which will be shortly described. The anterior spinal artery, though of considerable size, is yet of less calibre than the basilar, with which it is nevertheless in perfect continuity. The exit of the posterior pair of cerebellar arteries marks the middle of the medulla. These arteries are slightly asymmetrical, the left being a little in advance of the right. They' arise behind the point of origin of the 6th pair of cranial nerves. The anterior pair of cerebellar arteries arise just after the division of the basilar artery to form the carotids on each side; they are distinctly smaller than the posterior pair. The two branches of the basilar are approximately equal in size, as are the carotids which join them very shortly after the bifurcation of the basilar. The point of junction is just at the point of origin of the anterior cerebellar arteries. In this, it will be observed, is a slight difference from the figure of the cerebral arterial system of this Lizard given by Rathke *. The next artery arising from the circle of Willis is in front of the third nerve (to the inside of which nerve passes the forward continuation of the carotid, as in other vertebrates) and supplies chiefly the corpus bigeminum of its side ; but it also gives off a branch each to the cerebelhim and to the cerebral hemisphere. A little way anterior to this is a much more slender vessel which is absolutely symmetrical on both sides of the body and which almost at once divides into two branches; one of these ends upon the in-fundibulum, the other reaches the optic nerve of its side. Beyond this again arises the posterior cerebral artery. This artery reaches the hemisphere just at the furrow which divides it from the corpus bigeminum and runs parallel to the cerebral branch of the bigeminal artery. A little further forward the carotid finally divides into two arteries. The outer and stronger branch may be termed the middle cerebral; it runs forwards, curving outwards in the middle so as to be crescent-shaped, to the long and slender olfactory bulbs, giving off numerous slender branches to the hemisphere on its way. The inner branch very soon again divides into two : the innermost of them is the ophthalmic artery; the outer runs forward along the median ventral line of the brain in close contact with its fellow of the opposite side. * " Untersuclmngen iibcr die Aortenvviivzeln &c. der Saurier," Denksclir. k. Akad. Wiss. Wien, xiii. 1857, p. 51. [Since this paper was read Mr. R. H . Burne has kindly directed my attention to a paper by Dr. Hofmann in Zeitsclir. f. Morph, u. Anthr. ii. 1900, in which the arterial system of the brain is described in a number of Fishes, Amphibia, Birds, and Mammals, and in the following Reptiles, viz. Iguana, Tropidonotus natrix, Crocodile, and Testudo grceca. That of the last alone (among Reptiles) is figured. This paper has been apparently overlooked by the recorders of the Mammalia, Aves, and Reptilia in the ‘ Zoological Record' for 1900; but it is catalogued by the recorder of ‘ General Subjects."-July 6th.~\ |