60 MR. F. E. BEDDARD OX THE ENCEPHALIC [May 16, 



§ Brain o/' Iguana tuberculata. 



The plan of the cerebral arteries in this Lizard differs in a 

 number of particulars from that whicli 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 postei-ior 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 jvist 

 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 bifur- 

 cation of the basilar. The point of junction is just at the point 

 of origin of the anterior cerebellar ai-teries. 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 

 cerebellum 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 othei- 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 bi-ain in close contact with its fellow 

 of the opposite side. 



* " Untersuclmngeu iiber die Aortenwuvzeln &c. der Saurier," Denksclir. k. Akad. 

 Wiss. Wien, xiii. 1857, p. 51. 



[Since this paper was read Mr. E. H. Bunie has kiujlly directed my attention to a 

 paper by Dr. Hofmann in Zeitscbr. 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, Tropidonotits natri.v. Croco- 

 dile, and Testudo grtBca. 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." — Juli; Qt/i.] 



