DR. J. MURIE ON 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. 57), 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 which, 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 Manatus, 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 well 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 
