426 PROFESSOE OWEN OxNT MACROPUS. 



§ 3. Vertebrce. 



The atlas (PI. LXXV. figs. 1-4) is remarkable for the low, broad, flat roof of the 

 neural arch (ib. fig. 4, n, w,), 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 mdication of a neural spine. The ossification of 

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

 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 Avhich 

 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). 

 This retention of the typical relations ought not to be overlooked in homologizing the 

 sclerous basis (ib. fig. 2, h) beneath the centrum of the atlas, which unites, when ossified, 

 with the inferiorly produced ends of the nem-apophyses in the Bandicoots^ and Opossums. 

 The atlantal hypophysis in Thylacinus is produced backward as a spine. The diapo- 

 physes {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 Macro_pus has a less vertical diameter in proportion to its breadth, and 

 a lower and antero-posteriorly broader arch above the diapophyses ( 2', 2' ) than in 

 Phascolomys^. 



The centrum of the axis (PL LXXV. 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. j)l) is half an inch long, slender and obtuse ; a vertebrarterial foramen (fig. 8, v) is 

 completed by the confluence of the riblet (fig. 5,^^) with the par-(^j) and di-((Z) 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, <?, 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 

 oi 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. 



' Pander and D'Alton, op. cit. tab. vii. fig. c. 



- Art ' Marsnpialia,' torn. cit. p. 277, fig. 98, Perameles lagofis. 



' Cuvier notes this character in " lea didelphes and les kangaroos," in which " I'artcre ne traverse point du 

 tout I'apophyse transverse, elle pasae dessous et contourne son bord anterieur'" (Legons d'Anat. Comp. 8vo, 

 1835, torn. i. p. 189). 



■* Comp. figs. 1-4, pi. Lxix. vol. viii. of Zool. Trans. 1873. 



