136 DR. J. MURIE ON THE FORM AND STRUCTURE OF THE MANATEE. 
4th, numerical variability may occur in individuals of the same species apart from sex ; 
5th, if there are several distinct species, as some hold, the aggregate in each may be 
different. 
In reply to the first of these reasons, it is doubtless true that the tiny ossicles termi- 
nating the caudal region, and each of which represents a vertebral element, occasionally 
are lost; the total numbers therefore in such cases would be under the maximum. 
But this only accounts for one kind of deficiency, whereas differences in numbers are 
attributed to the cervical and dorsal vertebra, where the same excuse does not hold 
good. Concerning the second reason, here also non-ossification of the terminal caudals 
would give rise to the very young animal having a minimum of vertebre in the spine. 
But in this, as in the last, uniformity of regional numbers seemingly does not obtain. 
Third, the data extant showing relation of sex to spinal formula, does not prove that 
male and female possess a constant ratio the one to the other. The fourth proposition, 
I am of opinion, is the true explanation of the manifold discrepancies, excepting what 
concerns the cervicals. Professor Krauss, I may affirm, has had more Manatee skeletons 
pass through his hands than any other savant in Europe; and these have been received 
all from one locality, and undoubtedly of one species. His observations, most accurately 
made, are in every way trustworthy; and they go to show that the numbers of dorsal as 
well as lumbo-caudal vertebre are subject to irregularity. Results coming under my own 
notice substantiate his data. Fifth, specific distinction yields no very determinate data 
of spine-formulz, especially as concerns the supposition of distinctive American forms. 
It may be concluded, therefore, that the vertebral series of M/anatus is inconstant within 
certain limits, and in this respect presents resemblances to those of the Cetacea. 
Besides differences of opinion respecting the total number of vertebral elements, 
authorities also disagree as to the numbers and character of vertebra taken regionally. 
The singular J/anatus has thus afforded a moot case, every ray of light shed upon 
which brings out fresh features or readings of the facts. As regards the cervical region, 
two points have excited discussion :—one, whether six or seven was the normal number 
of bones; the other, which vertebra was the missing one, provided the mammalian law 
of seven was deviated from. The vantage-ground has latterly been ceded to those who 
have maintained the presence of but six osseous representatives. 
Of special observers as to the first point at issue, Sir Everard Home, Alex. vy. 
Humboldt, De Blainyille, Leuckart', and Robert? have enunciated that there are seven 
cervical elements ; whilst Daubenton, the brothers Cuvier, Meckel®, Schlegel, Stannius, 
A. Wagner’, Vrolik, Owen, Krauss, Brandt, Flower, and Gray, on more weighty grounds, 
have recognized only six clearly developed neck-vertebre. In both animals dissected 
by myself, only six appreciable neck-vertebre obtained. I thought I had detected the 
rudiment of a seventh in the young male; but a more scrutinizing search failed to justify 
* Zool. Bemerk. (Stuttgart, 1841), p. 62. ? Comptes Rendus, 1836, p. 363. 
§ Vergl. Anat. ‘ Schreb, Siiugethiere, Fortsetz, 1846, pt. 7. p. 106, 
