DR. J. MURIE ON THE FORM AND STRUCTURE OF THE MANATEE. 149 
upper nares, the greater amount going to the lip and and anterior infranarial region. 
The latter are sent inwards in distinct transverse lines, more particularly the deep layer. 
The section of this part thus resembles, on a small scale, the trunk of the Elephant 
when cut across—the tissue intervening between the muscular bundles and fibrille 
being fatty and fibrous. 
Many vessels penetrate the root and origin of this levator ; this, no doubt, led Vrolik’ 
to regard “ the structure of the upper lip as plainly an erectile tissue.” The true action 
of this muscle here may most plausibly be assumed to be a dilater of the nares. 
Deeper than the last, is a broad and thick plane of muscle, which, issuing from 
underneath the projecting orbit, proceeds forwards by parallel fleshy fibres, less broad 
than the preceding. These wind round the anterior portion of the intermaxillary, and 
lie above the buccinator, being inserted into the incisive fossa. ‘The upper border of 
this muscle, and its anterior portion, have apparently oblique fibres, which, being 
difficult to dissect, are readily cut across, and have a coarse aspect. These are what 
may represent the levator anguli oris, or be part and parcel of the combined levator 
labii proprius and levator anguli oris—here, however, not clearly separable. 
I name more than define a depressor labii superioris aleque nasi a thick mass of the 
deepermost fibres of the muscle just described, and partly continuous with the zygo- 
matici. These may represent, in a modified manner, the muscle in question. It is not 
at all clear or distinct, excepting by an alteration in the inner and narial fibres of these 
muscles. It seems to constitute a muscular layer directly in front of the intermaxillaries, 
stretching from the gum round the external aperture of the naris. 
The muscular layer the most superficial of those upon the muzzle, I take to be the 
equivalent of the levator labii superioris aleque nasi. It is of considerable thickness and 
great breadth, and almost throughout fleshy. Trapezoidal in figure, the four unequal 
sides respectively form the medio-nasal, the orbital, the labial, and the muzzle boun- 
daries. Fibres arise in a longish peaked manner from the outer side of the nasal 
cartilage upon the superior maxillary bone; thence they spread downwards and forwards, 
part winding outwards round the orbit, and part inwards to the nares; but the main 
body of the muscle has a median plane and covers the entire frontal superficies of the 
nares and upper lip. Below the nasal orifices, towards the median line, the fibres pass 
inwards curvilinearly, and are dovetailed with those of the levator labii superioris pro- 
prius, and partially inserted into the intermaxillary bones. They likewise cross above 
the nares and decussate with those of the opposite side of the face. 
Concerning this muscle’s action, the attachments and direction of its fibres show that 
it is an elevator, retractor, and dilater of the nares. 
Mandibular Arch and Side of Skull=Infracranial.—The muscles clothing the 
symphysial portion of the mandible greatly increase the remarkable appearance and 
unusual form of the bone of this region. Of these the levator labii inferioris is 
* Memoir cited, p. 59. 
