430 PEOFESSOE OWEN ON MACEOPUS. 



The chief vertebral characteristic of the Macropodidse is the strength and length of 

 caudal region, and the number of vertebrse composing it. In Macropiis rufus there are 

 twenty-two caudals, fourteen of which, after the second, have the haemal arch. The 

 metapophyses (PI. LXXVI. fig. 10, in, 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 as a pair of low ridges («s) 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 difi'ers from the first in the smaller postzygapophyses. The 

 haemal arch (fig. 11) is small, with a longish slender spine [h 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 preediapophyses (ib. fig. 12,])d), are 

 developed ; they are thence continued along a great part of the caudal region. 



The haemal arch is strengthened ; its spine shortened, but extended lengthwise (fig. 13, 

 /* s). 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 haemapophyses articulate with the tubercular exjDansions of the hypapophyses by 

 almost fiat subcircular surfaces (figs. 14-16, h, k), which coalesce in the fifth and 

 succeeding vertebrae, circumscribing the haemal arch or canal exclusively of the centrum. 

 These htemal 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 

 haemal spine is greatest in the seventh caudal (fig. 13, h s, h s'). Beyond this the haemal 

 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 (PI. LXXVIII. fig. 1) is broad in proportion to its length ; the supra- 

 spinal plate (/) extends so as to describe a bold convexity (^') along the major part of 

 the upper border or " costa ;" and the infraspinal plate {f) expands to the rounded post- 

 inferior angle of the bone (li) ; both tracts are almost flat, and the supra- and infra- 

 spinal fossae 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 



