430 PROFESSOR OWEN ON MACROPUS. 
The chief vertebral characteristic of the Macropodide is the strength and length of 
caudal region, and the number of vertebree composing it. In Macropus rufus there are 
twenty-two caudals, fourteen of which, after the second, have the hemal arch. The 
metapophyses (Pl. LX XVI. fig. 10, m,m) resume a considerable size in the first caudal, 
in the form of quadrate plates an inch in length by eight lines across the truncate ends; 
the lower half of the fore border is slightly produced as a zygapophysis (z), the surface 
of which is continued back upon the base of the metapophysis. The neural spine is 
represented asa pair of low ridges (ns) diverging to the postzygapophyses (z’,z'). These, 
in the first caudal, resemble those of the second sacral. ‘The diapophyses, developed in 
both first and second caudals from the hinder half of the confluence of centrum with 
neurapophysis, are depressed plates, extending horizontally outward and backward, 
where they end in obtuse rather thickened points (ib. fig. 10, d, d). 
The second caudal chiefly differs from the first in the smaller postzygapophyses. The 
hemal arch (fig. 11) is small, with a longish slender spine (/ s). 
The third and following caudals have no zygapophysial junctions, but coarticulate by 
their centrums only. ‘The diapophyses are much diminished in the fourth caudal, and 
are reduced to tuberosities terminating the sharp lateral longitudinal ridges of the 
centrum in the fifth caudal. In this vertebra the prediapophyses (ib. fig. 12, pd), are 
developed; they are thence continued along a great part of the caudal region. 
The hemal arch is strengthened ; its spine shortened, but extended lengthwise (fig. 13, 
hs). A pair of hypapophysial ridges, beginning in the third caudal, form the sides of 
a canal at the fore part of the fifth and following caudals (fig. 12, hy). 
The hemapophyses articulate with the tubercular expansions of the hypapophyses by 
almost flat subcircular surfaces (figs. 14-16, h,/), which coalesce in the fifth and 
succeeding vertebrie, circumscribing the heemal arch or canal exclusively of the centrum. 
These hemal arches develop ectapophyses (ib. figs. 15, 16, e,e), which are vertical 
homotypes of the diapophyses of the neural arch. The fore-and-aft extension of the 
hemal spine is greatest in the seventh caudal (fig. 13, 1.s,/s'). Beyond this the hemal 
spines gradually decrease (ib. figs. 15 & 16), and the arch is finally reduced to simple 
lozenge-shaped plates overlying the joint between two caudals. I find the last of 
these at the antepenultimate of such caudal joints in Macropus rufus. 
§ 4. Bones of the Fore Limbs. 
The scapula (Pl. LXXVIII. fig. 1) is broad in proportion to its length; the supra- 
spinal plate (i) extends so as to describe a bold convexity (g') along the major part of 
the upper border or “ costa;” and the infraspinal plate (7) expands to the rounded post- 
inferior angle of the bone (h); both tracts are almost flat, and the supra- and infra- 
spinal fosse are comparatively shallow. 
The glenoid cavity (ib. fig. 2, d) has the usual ovate form, with the small end next 
the coracoid (c). The outer border, or that next the acromion (e), is sharp and rather 
