DR. J. MURIE OX THE FORM AND STRUCTURE OF THE MANATEE. 187 



from them by narrow canals, each nearly a couple of inches long, and which open by 

 two crescentic horizontally placed orifices on the summit of the truncated snout. Each 

 narrow anterior canal, and its terminal crescentic narial orifice, are surrounded by and 

 perfectly under the control of the powerful nasal muscles already detailed. The 

 anterior nares are situated about half an inch apart from each other (rather less in the 

 young male), and they individually have about as much vertical and transverse diameter 

 when dilated. When contracted they appear simply flattened semilunar transverse slits 

 at the top of the corrugated fleshy snout. 



The olfactory passages may conveniently be regarded in the Manatee as consisting 

 each of three compartments. Behind is the postnarial chamber, partially divided in 

 front from its fellow of the opposite side by the vomer and septal cartilage. Below, it 

 is wide and somewhat tubular ; above, it is narrowed and outwardly curved, or follows 

 the outline of the turbinal, thus forming a lower and an upper meatus. 



In advance of the postnares, and without any decided constriction from the posterior, 

 is the median narial chamber {n.ch, fig. 37), namely that portion covered by the nasal 

 cartilages. In front this is very narrow; and its floor forms a kind of cul de sac just 

 behind the prominent premaxillary rostrum, above Avhich, or at its top, is the narrow 

 cartilaginous opening already spoken of. From this point forwards is the anterior 

 compartment, or narrow tubular passage heretofore described. 



A highly vascular layer of Schneiderian membrane lines the two so-called posterior 

 nasal chambers ; but as it reaches the anterior canal it assumes more of the character of 

 an ordinary mucous membrane, and at the semilunar nasal orifice is livid, and apparent 

 less delicate and sensitive than are the internal chambers. 



As regards the sense of smell possessed by Manafus, I am not aware it is gifted with 

 delicate olfactory perception ; at least I do not know of any observations on the living 

 animal to substantiate such an assertion. If, however, size of olfactory bulb tally with 

 the function of smell, this faculty is far from deficient. 



2. Ocular and Auditory Apparatus. 

 Compared with the orbital cavity the eye is most diminutive ; around it, however, 

 are fatty tissues, a manifest vascular rete, a great bunch of infraorbital nerves, &c. ; so 

 that the space is Avell packed. Divested of adventitious structures, the ball of the eye 

 has a diameter a trifle over half an inch, and is nearly spherical. The pupil, as far as 

 I could judge, inclines to a transverse oval, and is less than 0-2 inch in diameter. The 

 crystalline lens is proportionally small, and with an antero-posterior compression. Ante- 

 riorly the sclerotic thins, but posteriorly (as in Cetacea) is relatively very thick and 

 dense. The convexity of the cornea is but moderately protuberant, the aqueous chamber 

 therefore small or perpendicularly high ; the vitreous chamber also has a vertical dia- 

 meter greatly in excess of its horizontal one. Ciliary processes are abundant, and 

 furnished with pigmentum nigrum ; and the tapetum, though lighter in hue, neverthe- 

 less has a delicate choroidal layer of pigmentary matter. A third eyelid or nictitating 



