186 DR. J. MURIE ON THE FORM AND STRUCTURE OF THE MANATEE. 
the indicial and second digits. Twigs from it, moreover, supply the parts at the wrist- 
joint. About the head of the radius the posterior interosseous division from the radial 
takes a course along that bone. The ulnar nerve on reaching the inside of the olecranon, 
thereafter divides into three. A large cord goes to the root of the fifth digit and supplies 
the parts on it and the fourth. ‘The second, also a thick cord, is imbedded within the 
dorsal aspect of the palmaris and flexor carpi ulnaris muscles, accompanying them to 
the pollicial metacarpal, and then breaks up on the same. The third division is mus- 
cular, chiefly devoted to the palmaris and flexor ulnaris. 
IX. Sensory ORGANS. 
1. Nose and Nasal Passages. 
The Sirenia differ very materially from the Whale tribe in the form, structure, and 
general nature of the nasal organs. Neither has their nose close outward resemblance 
to the great nasal trunk of Proboscidea, nor even to the more curtailed appendage of 
the Tapiride. In fact, it might as deftly be compared to the snout of the Suide as 
either of these, though, strictly speaking, it is unlike either. The great furrowed and 
bristle-clad semilunar upper lip and truncate snout of Manatus have been fully described 
by preceding writers; and each notes the pair of narial orifices on the top of this, just 
as it shelves to the perpendicular. ‘This position of the nares is a seeming rather than 
real approach to the type of Cetacea, yet altogether dissimilar. Examination shows 
that were the trunk of an Elephant cut short at the root, or, better still, left entire, but 
contracted to a minimum of its long diameter, and with the terminal tactile appendage 
aborted, structurally the Manatee’s naso-labial organ would assimilate with it. 
The nasal and facial muscles I have described and compared with those of Elephant 
and Whale in the chapter on the myology, and, before treating of the interior nares, 
repeat that there are no appendicular sacs whatsoever as in the latter marine form. 
The nasal cartilages are very simple. There is a thick septal cartilage (sp, fig. 38, 
Pl. XXVI.), the continuation of the vomerine rostrum, and which fills the grooved canal 
on the floor of the nares. It slopes down from the anterior mesial edge of the frontal 
bones to the proximal part of the osseous premaxillary rostrum, where it stops short. 
Upper lateral and alar cartilages cannot be separated ; but what represents the former 
or both (nc) is a superior cartilaginous narial roof or outfolding of the septum. On 
each side this covers the large anterior narial vacuity or chamber (n.ch, fig. 37) in a 
convex manner, being fastened to the bone exteriorly from the frontal along the 
inferior inner edge of the nasal and premaxillary to the root of its rostrum. On 
nearing the latter point it splits; or its mesial portion, that in connexion with its fellow 
of the opposite side, continues as a splint along with the septal cartilage forwards, and 
is separated from the outer fork by a long and narrow oblique fissure (ef. fig. 38). 
The two anterior cartilaginous fissures, as looked at from above, have an acute 
V-figure, and fall short of the outer nares, the nasal passages being continued forwards 
