52 ME. F. B. BEDDAED ON THE [Jan. 19, 



reason of the marked separation of the two ventricles (not so 

 marked, however, as in the Dugong), and by the conspicuousness 

 of the coronary arteries which ramify over its surface; the organ 

 is also, as has been I'emarked, small for the size of its possessor. 

 I fonnd that in M. inunguis the ductus arteriosus was perfectly 

 permeable and was a tube of some size ; in the heart of a young 

 AI. latirostris a little more than half its size, the ductus was tube- 

 like in form and had an orifice into the pidmonary artery, but was 

 apparently not permeable throughout. In the M. latirostris with 

 a heart twice the size, the ductus was absent or rather represented 

 by a flat non-tubular ligament. This seems to indicate a specific 

 difference between the two forms in the relative age at which the 

 ductus arteriosus degenerates. But it is, on the other hand, quite 

 likely that there are variations in respect of this. The right 

 ventricle in all three specimens "was less sculptured on its inner 

 surface than the left. It has in all three a moderator baud, which 

 is most pronounced in if. inunguis. This moderator band in that 

 species is continued forwards after it has become adherent to the 

 ventricular wall to the base of one of the semilunar valves of the 

 pulmonary artery. In the young M. latirostris this was so to a 

 less extent ; while in the larger 31. latirostris the moderator baud 

 was free from the heart-wall for a less extent and did not run 

 forwards to the base of the valve at all. I observed no differences 

 in the mode of origin of the principal arteries of the aorta in the 

 three specimens. 



The brain of Manatus latirostris has been described and figured 

 by Murie', Chapman-, Garrod*, and by Murie ' again. Of these 

 the last-mentioned paper appears to me to contain the best figui-es. 

 I have in my possession a brain of that species which differs 

 slightly from previously described brains ; the drawing (fig. 5, p. 5;^) 

 will also enable me to compare more satisfactorily the two species 

 in respect of their brain structure. 



This organ in fact shows certain slight but characteristic 

 differences in the two Manatees. In the first place there is the 

 shape when the brain is viewed from above : in M. inung^iis the 

 cerebral hemispheres are markedly longer in proportion to their 

 breadth, the two dimensions being, as nearly as I could measure, 

 65 mm. and 30 mm. ; on the other hand, in my specimen of 

 M. latirostris the same measui'ements were 65 mm. and 37 mm., 

 about the same as those of the brain figured by Garrod. The 

 outline of each hemisphere is more distinctly C-sliaped in M. inun- 

 guis, the C's being of course back to back. The only fissures of 

 the hemispheres in M. immguis are the Sylvian, both of Mhich are 

 Y-shaped above. Seen laterally each fissure runs forward near 

 to its termination ; but the forwardly directed part of the fissure 

 is, in my opinion, the rhinal fissure, which does not, at least so 



' " On the Form and Structure of the Manatee," Tr. Z. S. viii. p. 627. 

 - " Obseryations ou the Structure of the Manatee," Proc. Acad. Nat. Sci. 

 Philad. 187.">, fig. 45i 



'■> "Notes on the Manatee, &c.," Tr. Z. S. x. p. 137. 



' "Further Observations on the Manatee," ibid. xi. p. 19. 



