OF THE THREE-TOED SLOTH. 115 
est oblique, se baissant un peu en avant, et y rentrant un peu endedans. La huitiéme 
ala sienne un peu fourchue. La neuvieme l’a prolongée en une petite pointe qui se 
porte en avant et en dehors. Dans le jeune individu cette partie n’est pas soudée a la 
vertébre ; seroit-ce un petit vestige de cote ?’’! 
In the second edition of the ‘Régne Animal’ occurs the following observation, 
showing what were the latest views of Cuvier on this subject. ‘‘C’est le seul mam- 
mifére connu jusqu’a ce jour qui ait neuf vertébres cervicales.’’2 
The nearest approach which has hitherto been made to the true bearing of the fact, 
is contained in the following passage from Meckel. Speaking of the points of ossifi- 
cation or nuclei in the cervical vertebra, he says, ‘‘ In the last are found a fourth and a 
fifth [nucleus], constituting, as it were, rudiments of ribs, projecting from the sides. In 
Man this elongated bone forms the anterior root of the transverse process, and extends 
from the body to the posterior root of that process. In the Ai a very considerable bony 
nucleus is articulated by means of a broad cartilage to the end of the transverse process 
of the ninth cervical vertebra ; by means of which this vertebra becomes suddenly much 
broader than the rest. In the other Mammalia which I have examined, this bony nu- 
cleus is wanting. It is remarkable that in the Ai an analogous but much smaller bony 
nucleus is found attached to the same situation in the eighth cervical vertebra ; so far as 
this goes, these two vertebre become similar to dorsal, and thereby the exception which 
the Ai makes in this particular to other Mammalia is lessened.’3 
From this passage it is evident that Meckel still considered the two vertebre in 
question to be truly cervical, though approaching to the character of dorsal vertebre. 
The fact, however, that the rudimentary ribs remain permanently moveable, of which it 
would appear that both Cuvier and Meckel were ignorant, at once proves that these 
vertebre are not only approaching to the dorsal form, but are essentially dorsal, if it be 
a true character of a rib, as distinguished from a transverse process, that it is perma- 
nently moveable. This is a question certainly of considerable interest, but one into 
which it is not necessary on the present occasion to enter, as the fact of the permanent 
mobility of the rudimentary ribs in the 4%, the perfect construction of the capsular 
ligament, and the cartilaginous surfaces of the joint are sufficient, joined with the ex- 
istence of a foramen for the passage of vessels and other circumstances in their struc- 
ture and situation, to establish their character beyond all doubt. The rule therefore 
which assigns seven cervical vertebre to the whole of the Mammalia, is thus left with- 
out a single exception. 
The interesting paper of Professor Buckland on the habits of the Sloth, lately read at 
the Linnean Society, precludes the necessity of my entering into any lengthened specu- 
lations on the utility of this singular structure ; I may, however, remark, that the fact 
1 Ossemens Foss., tom. v. p. 83. * Régne Anim., (ed. 2.) tom. i. p. 252, 
8 Syst. der Vergleich. Anat., B. ii. pl. 2. p. 294. 
VOL. I. R 
