100 REPORT — 1856. 



bordered bj' enamel, is exposed. There is also an anterior and posterior low barrel 

 ridge ; the posterior one being most developed in the lower molars. The upper 

 molars have each three diverging roots, one on the inner and two on the outer side. 

 The lower molars have two fangs. Dr. Vogel's description of the grinders, as 

 "having six points and three roots each," would apply to the upper molars of the 

 M. Senegalensis before they had been much worn*. As to the number " five," that 

 doubtless refers to the number forming tlie series of teeth on each side of the jaw. 

 I have not had the opportunity of examining the dentition of the known African 

 Manatee. In the figure of the skull of the M. Senegalensis given by Cuvierf, six 

 molars are shown on the right side of both upper and lower jaws, and the coronoid 

 process of the mandible may hide a greater number. In the American Manatee I 

 have ascertained that at least nine molars are developed on each side of both jaws X, 

 but they are never simultaneously in place or use. The greatest number which I 

 have found in that condition is seven, the socket of a shed anterior molar being at 

 one end of the series, and that containing an incomplete ninth molar at the opposite 

 end. Prof. Stannius has observed a small simple conical molar anterior to the nor- 

 mal two-ridged molars, and divided by a narrow interval from them, in a new-born 

 American Manatee. The individual Ajuh, 5 feet in length, which appears to have 

 been more especially the subject of Dr. Vogel's account, was a half-grown animal, 

 and the number of grinders (five), as well as their six-pointed crowns, doubtless 

 relate to that circumstance. Fifteen feet is said to be the length to which adults of 

 the M. Senegalensis attain: the Ajuh becomes 10 feet long. It maybe a distinct 

 and somewhat smaller species. The chief indication, however, of such specific di- 

 stinction is the closer approximation of the eyes to the nostrils and to the end of the 

 snout, as shown by the admeasurement given by Dr. Vogel. The easiest procura- 

 ble and transportable evidence of the Ajuh, and the best calculated to determine 

 this point would be the skull ; but every part would be most acceptable ; and, in the 

 meanwhile, the species may be indicated and kept before the notice of the naturalists 

 by entering the Ajuh in the Zoological Catalogue as the Manatus Vogelii, or Vogel's 

 Manatee. 



Experimental Researches on the Eye, and Observations on the Circulation of 

 the Blood in the Vessels of the Conjunctiva, of the Iris, of the Ciliary 

 Ligament, mid of the Choroid Membrane, during life, as seen under the Com- 

 pound Microscope. By Augustus Waller, M.D., F.R.S. 

 Dr. A. Waller states, that his observations are founded in great measure on the 

 fact observed by him some months since, that the eye may be obtained sufficiently- 

 protruded from the cavity of the orbit to render its deep-seated parts accessible to 

 direct observation. 



Artificial exophthalmosis of this nature, he finds from experiment, may be easily 

 produced in various animals, sufficiently to expose the anterior two-thirds of the 

 eyeball and to observe the circulation oyer the greatest portion of the vessels of the 

 choroid. 



While in this state the iris may be made to contract by light, and there is reason 

 to suppose that the organ of the animal still possesses the powers of vision. 



The eye is obtained in this state by opening widely the eyelids, and by exercising 

 a slight lateral pressure on the eye, which causes the ej^eball to escape through the 

 opening of the eyelids ; returning to its original situation as soon as the pressure is 

 removed. 



For his experiments. Dr. Waller employs the rabbit, the guinea-pig, and the Mus de- 

 cumanus or rat, all of them of the albinos variety, and more especially the albinos rat. 

 In these animals, by means of the light passing through the pupil and through the 

 sclerotica, the organ may be sufficiently illuminated by transmitted light to enable 

 us to observe, under the compound microscope, the different parts of the eye as a 

 transparent object. 



The body and the eye of the animal are fixed by using a roll of linen like a swad- 

 dling band, and then tied to a piece of flat cork, the eye at the same time being pro- 



* Cuvier figures a similar molar of the M. Americanus in pi. 220. fig. 11. 

 f hoc, cit., fig. 4. + Odontography, vol, i. p. 371, pi. 90. fig. 2. 



