754 
PROFESSOR OWEN ON THE MEGATHERIUM. 
Strong' single ridge developed into a tuberosity in most of the cervical vertebrae. 
The atlas has a bypapophysis in most Ruminants. 
In the Musk-deer the deutata has a sharp hypapophysial ridge, extending from 
below the base of the odontoid to beyond its posterior surface, where it underlaps 
the next vertebra. A similar ridge, ending in a backwardly produced process, is 
developed from the two succeeding cervicals ; beyond which the hypapophysis gra- 
dually subsides to the seventh cervical. 
In the Camel {Camelus hactrianus) the atlas has no hypapophysis; but this com- 
mences as a ridge from the hinder half of the centrum of the dentata, expands as it 
proceeds backwards, and divides into two tubercles. In the third and fourth cervicals 
it is principally represented by the pair of posterior tubercles, which subside in the 
fifth cervical vertebra. 
The dentata of the Giraffe has a strong hypapophysial ridge from near the fore- 
part of its body. 
In the Monotremes the atlas is remarkable for a modification of the hypapophysis, 
similar to that which it undergoes in the caudal vertebrae of most Mammals; it 
forms, e. g. a pair of processes which diverge from one another: in the succeeding 
cervicals the hypapophysis is single. 
As the aim of the present communication is to demonstrate the individuality and 
distinctness of the exogenous processes, and their title to distinct names, the modifi- 
cations of each in any given class will not be traced further than appears requisite to 
attain the proposed end : and I shall conclude the present notice of the exogenous 
processes in the Mammalian class, by applying the principles and nomenclature above 
defined to the description of some caudal vertebree. 
Plate LIII., fig. 60, is the first caudal vertebra of the Mijrmecophagajuhata, in which 
the heemapophyses h h are superadded and articulated to the hypapophyses hy hy, form- 
ing a heemal arch : in the succeeding vertebree the heemapophyses coalesce at their 
lower ends, and develope a true inferior or heemal spine. n,n, are the neurapophyses ; 
ns, the neural spine; 2 , the zygapophyses, here coexisting with m the rnetapophyses. 
The transverse process is long and single on each side, and consists of an exogenous 
base or ‘ diapophysis,’ d, and an anchylosed ‘ pleurapophysis,’ pi. 
Fig. 61, A, is an upper view of the seventh caudal vertebra of a Beaver {Castor 
fiber), where nn are the neurapophyses, which have ceased to coalesce with each 
other and complete the neural arch : mm are the rnetapophyses ; dd are the anterior 
diapophyses, and d' d' the posterior diapophyses. Fig. 61, b, gives an under view of 
dd and d' d', and of the hypapophyses, hh. Fig. 61, c, is the front view of the same 
vertebra, showing n, mm, d d, and by. 
Fig, 62, A, B, c, is the ninth caudal vertebra of the Kangaroo; w'w' are the neur- 
apophyses, which, coalescing at n, form the neural arch, now reduced to its smallest 
dimensions: m,m are the rnetapophyses; all trace of zygapophyses or articular 
processes has now disappeared from both the neur- and rnet-apopbyses : dd are 
