175 



December 10, 1839. 

 William H. Lloyd, Esq., in the Chair. 



A letter from Dr. Weissenborn, dated Weimar, October 6, 1839, 

 was read. It accompanied a present of two specimens (male and 

 female) of the black variety of the common Hamster (Cricetus vul- 

 garis), and a head, preserved so as to display the cheek-pouches of 

 that animal. The writer of the letter states that he possesses a 

 common Pigeon, just fledged, in which no vestiges of the organs of 

 vision can be traced. " The orbits are tolerably well developed, and 

 lined with a sort of half-mucous membrane, and therefore destitute 

 of feathers. I have never heard of a similar defect in any animal ; 

 and in one where the incubation is extra-uterine it appears doubly 

 wonderful or anomalous. The bird is quite healthy, and presents in 

 its habits several curious anomalies, which may be traced to its mon- 

 strosity." 



Professor Owen communicated his notes on the Anatomy of the 

 Biscacha (Lagostomus trichodactylus, Brookes). 



" The individual dissected," says Mr. Owen, " was a female, full- 

 grown, weighing 8 pounds 2 ounces, avoirdupois : the weight of the 

 brain was 5 drachms, avoirdupois, the proportion of the brain to the 

 body being as 1 to 416. This is the smallest relative size of the 

 brain that has yet been recorded in the Rodent order, in some of the 

 species of which order, as the Mouse, the brain approaches that of 

 Man, the relation of its mass to that of the body being as 1 to 46 ; 

 that of the human subject is as 1 to 30. The brain presented the 

 usual broad depressed form and simple unconvoluted surface charac- 

 teristic of the Rodent order : its length was 1 inch 8 lines, its breadth 

 1 inch 5 lines, and the length of the cerebral portion 1 inch 3 lines. 

 The proportion of the cerebellum to the cerebrum was as 1 to 5. 

 The breadth of the medulla oblongata was to that of the cerebrum as 

 1 to 6. The upper surface of each lobe of the cerebrum is marked 

 with two slightly curved fissures, each between 3 and 4 lines in 

 length, and one a little in advance of, and exterior to the other : a 

 single anfractuosity defines the external convex prominence of the 

 cerebrum. On the under surface a fissure is continued from the 

 posterior part of the cerebral hemisphere forwards, along the middle 

 of the natiform protuberance, to the outer boundary of the root of 

 the large olfactory nerve. 



On laying open the abdomen an immense accumulation of adipose 

 membrane concealed the viscera ; the bag of the great omentum 

 formed, however, a small part of this covering, as after extending 

 down over half the abdomen it was reflected upwards, in front of 

 the liver. The lower half of the abdominal cavity was overlapped 



No. LXXXIV. PfiOCEEDINGS OF THE ZOOLOGICAL SoClETY. 



