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and they are here noted as guides in the comparison of fossil cranial parts of Macro- 

 podidae. 



§ 3. Vertebrae. — The atlas (PI. LXVII. figs. 1-4) is remarkable for the low, broad, 

 flat roof of the neural arch (ib. fig. 4, n, n,), which extends almost transversely across 

 from the upper ends of the articular cups (fig. 2, z, z) for the condyles of the occiput. 

 A small tubercle (ib. fig. 2, ns) at the fore margin of the arch (the origin of the " rectus 

 capitis posticus minor") is the sole indication of a neural spine. The ossification of 

 the neurapophyses (n, n) below the condylar cups (z, z) does not extend, as in Halma- 

 turus thetis, so as to complete the arch. An interspace of a line and a half intervenes, 

 in M. rufus as in M. major, between the obtuse ends of those elements, above which 

 the centrum of the atlas projects (as an " odontoid process," ib. figs. 5, 6, c, a) with an 

 articular lower surface, which rested on the ligament (indicated by dotted lines in fig. 2, h) 

 and rotated upon corresponding facets at the ends of the neurapophyses (ib. np, np). 

 The diapophyses (d, d) are continued outwards from the upper and hind part of the 

 neurapophyses, and expand to their free end, which is produced forward and backward, 

 most so and more pointedly forward. The neurapophysis is perforate above the fore 

 part of the base of the diapophysis, at fig. 1, by the first spinal nerve; posteriorly it 

 is deeply grooved above the postzygapophysis (fig. 3, z') by the vertebral artery. The 

 atlas in Macropus has a less vertical diameter in proportion to its breadth, and a lower 

 and antero-posteriorly broader arch above the diapophyses (1?, 2' ) than in Phascolomys 

 (PI. XCVIII. figs. 1-4). 



The centrum of the axis (PI. LXVII. fig. 5, c, x) is subcarinate below and shows a 

 pair of venous foramina (fig. 6, c, x) near its posterior third. The pleurapophysis 

 (ib. pi) is half an inch long, slender and obtuse ; a vertebrarterial foramen (fig. 8, v) is 

 completed by the confluence of the riblet (fig. 5, pi) with the par-Q>) and di-(d) apophyses. 

 The neural spine (ib. fig. 5, n. s) is coextensive with the arch, and is produced anteriorly 

 so as to overhang the base of the odontoid (ib. fig. 5, c, a); its hind border is vertical ; a 

 pair of tubercles project at the sides of the angle formed between the hinder and the 

 upper almost straight border. The prsezygapophyses (figs. 5 & 6, z) cover the fore part 

 of the centrum on each side of its confluence with that of the atlas (ca) : the postzyga- 

 pophyses (fig. 5, z) extend a little beyond the hind border of the neural spine. 



The transverse processes of the other five cervical vertebras are perforated. The 

 spine of the third is compressed, laminate, truncate, coextensive with the neural arch ; 

 in the fourth (ib. fig. 7, ns) it contracts antero-posteriorly, loses height, but gains in 

 breadth at its summit ; this character of the spine increases in the fifth ; the spine 

 lengthens and becomes obtusely pointed in the sixth, is still longer and more merits 

 the name of spine in the seventh cervical (ib. fig. 9, c, ns). The parapophysis projects 

 as an angular plate in the fourth (ib. fig. 7, p) and fifth, and more so with increased 

 thickening in the sixth (ib. fig. 8, p) ; it is reduced to a mere tubercle in the seventh 

 cervical, in which the pleurapophysis is longest and strongest. The neural arch is 



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