186 PE. J. MUEIE 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 poUicial metacarpal, and then breaks up on the same. The thii'd division is mus- 

 cular, chiefly devoted to the palmaris and flexor ulnaiis. 



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 Tapiridse. In fact, it might as deftly be compared to the snout of the Suidse as 

 either of these, though, strictly speaking, it is unlike either. The great furrowed and 

 bristle-clad semilunar upper lip and truncate snout oi 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 tlie 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 (cf. 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 



