FROM QUATERNARY DEPOSITS IN THE VALLEY OF MEXICO. 
71 
The postzygapophyses are small in Palauchenia (Plate V. fig. 1, z'), showing similar 
proportions to those in Auchenia (fig. 2, z') ; in Camelus (fig. 3, z') they are more abruptly 
expanded and, as it were, pedunculate. From the outer side of the postzygapophysis 
a low ridge (fig. 1, r) extends obliquely downward and forward to the fore part of the 
diapophysis ; in Auchenia this ridge is directed toward the upper nerve-outlet (fig. 2, e ), 
and subsides before it attains thereto ; in Camelus (fig. 3) the ridge is wanting. The 
loftier and stronger neural arch and spine of the second cervical in Camelus (fig. 3, n.s.) 
give it proportions more like those of ordinary Puminants ; in the longer and more 
slender form of the vertebra Palauchenia resembles Auchenia. 
In an old Lama I have seen a pair of sharp longitudinal ridges (fig. 2, s) at the under 
part of the second cervical centrum, midway between the beginnings of the hypapophysis 
(hy) and the diapophysis (d); a low ridge on each side the beginning of the hypapophysis 
indicates the same relation to muscular attachments in Palauchenia : there is no trace 
of this character in Camelus. 
The third cervical vertebra of Palauchenia (Plate IV. figs. 5 & 6, 3, and Plate VI. 
fig. 1) lacks, accidentally, the hind half of the neural arch with the postzygapophysis 
and the right pleurapophysis ; sufficient, however, remains to well test the degree of its 
correspondence, respectively, with the same vertebra in Auchenia (Plate VI. fig. 2) and 
in Camelus (ib. fig. 3). In these existing genera the contrast and conformity respec- 
tively with the fossil, in the proportions of the third cervical, are greater than that in the 
second, the Camel’s vertebra assuming more breadth and height in relation to its length. 
Palauchenia strikingly resembles the Auchenian type in the general shape and pro- 
portions of the third cervical. The length of the centrum is 7 inches 3 lines ; the vertical 
dimension at the ends of the pleurapophyses (pi) is 3 inches 8 lines: in Camelus the 
length of the centrum is 6 inches 9 lines ; the vertical dimension at the ends of the 
pleurapophyses (pi) is 5 inches 6 lines; as this is the place of greatest vertical diameter 
of the third cervical in both Camel and Lama, the mutilation of the fossil vertebra does 
not affect the application of this comparative admeasurement. The third cervical of a 
large Lama (ib. fig. 2) yields 4 inches 6 lines, and 2 inches 3 lines, in the above dimen- 
sions. 
The fore part of the centrum is convex in Palauchenia in the degree it presents in 
Auchenia , and is less convex than in Camelus ; in each of these the ball does not fit into 
a corresponding cup at the back of the second cervical centrum, but works in one con- 
tributed chiefly by the intervertebral concentric ligamentous substance. In the flatness 
of the hind surface of the centrum Palauchenia agrees with Auchenia ; in Camelus it is 
convex at the periphery, slightly depressed at the centre. 
The hypapophysial ridge (Plate IV. fig. 5 ,hy, & Plate VI. fig. 1, hy) commences in 
Palauchenia more in advance than in Auchenia (fig. 2, hy), which otherwise it seems to 
resemble ; but the terminal tuberosity is broken off in the fossil. 
The pleurapophysis (Plate VI. fig. 1 , pi) resembles in position, direction, and length 
