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UNITED STATES NATIONAL MUSEUM BULLETIN 2 94 



AtL/\s. — Not unusually thick, with broad (anteropos- 

 teriorly) neural arch; anterior facets (pi. 17, fig. 1) for 

 articulation with occipital candyles of skull deeply con- 

 cave, widest near middle of height and slanting ob- 

 liquely outward from internal to external margins, the 

 two facets separated ventrally by a narrow' shallow 

 groove (trough). On eacli side, the neural arch (neura- 

 pophysis) is pierced ventrally near its anterior border 

 by a vertebra-arterial foramen (pi 18, fig. 1) which 

 opens externally into a ventrally directed groove. Neural 

 spine thick and short, with adjacent surface of arch ru- 

 gose and pitted. Transverse process on each side short, 

 blunt, almost three-sided in shajje. Neural canal large. 

 The two opposite posterior facets (pi. 17, fig. 2) for ar- 

 ticulation with the axis are broad, their external mar- 

 gins set ofl' from the lateral surface of the centrum. The 

 hyapophysial facet below the neural canal is short, acu- 

 minate, and vestigial. Between opposite posterior facets 

 and below the neural canal is the broad upward and 

 forward sloping surface for articulation with the odon- 

 toid process of the axis. A broad downward and back- 

 ward slanting articular surface, for the reception of the 

 forward projecting angle of the neural arch of the 

 axis, occupies the posterior border of the neural arch 

 medially. 



Additional measurements of USNM 23636 are as fol- 

 lows: Greatest distance between outer margins of an- 

 terior articular facets, 150 mm.; greatest distance be- 

 tween outer margins of posterior articular facets, 151 

 mm. ; greate.st vertical diameter of right anterior articu- 

 lar facet, 101 mm. ; greatest vertical diameter of right 

 posterior articular facet, 79 mm. 



Axis. — Characterized in part by large rugose three- 

 sided neural spine (pi. 17, fig. 3) arising from top of 

 neural arch. Transverse processes elongated, dorsoven- 

 trally widened on basal half, attenuated distally, di- 

 re<;ted downward but strongly bent backward. Foramen 

 transversarium on transverse process for cervical ex- 

 tension of thoracic retia mirabilia reduced to a small 

 opening (passage) less than the diameter of a pencil; 

 a rather deep cavity or depression on the posterior 

 face (pi. 17, fig. 4) of each process occupies the area 

 where, a larger opening originally was located. The 

 width of the neural canal exceeds its height. The rather 

 rugo.se anterior facets for articulation with the atlas 

 are, somewhat flattened, the vertical diameter of each ex- 

 ceeding its transverse diameter. The odontoid process is 

 short, acuminate. The anterior median angle of the neu- 

 ral arch is extended forward noticeably beyond the level 

 of the anterior facets to articulate with or rest on an 

 opposing surface on the posterior median border of 

 the neural arch of the atlas. The neural arch is massive. 



its lateral surfaces unusually rugose and sculptured. 

 The floor of the neural canal is shallowly concave ; the 

 wide ventral surface of the centrum is roughened by a 

 number of irregular small excrescences. The broadly el- 

 liptical posterior face of the centrum is flattened, shal- 

 lowly concave medially. The greatest distance (USNM 

 23636) between outer margins of anterior articular 

 facets is 153 mm. 



Third cervical. — The anterior face of the centrum is 

 broadly elliptical, bluntly rounded laterally, wider than 

 those of the following cervicals and shallowly depressed 

 medially, but the anteroposterior diameter of the cen- 

 trum (pi. 18, fig. 3) is less. The transverse diameter of 

 the neural canal (pi. 17, fig. 5) exceeds its vertical diame- 

 ter. The pedicles of the neural arch are short and thick 

 (minimum transverse diameter, 37 m.) , and support the 

 prezygapophysial facets which are largely destroyed. 

 The postzygapophysial facets are elongated, almost flat 

 and project at least 10 mm. beyond the level of the poster- 

 rior face of the centrum. The neural arch is lightly con- 

 structed and is very rugose dorsally; the neural spine 

 is short. The upper rather slender transverse process 

 (diapophysis) projects outward and backward and is 

 united distally with the end of the stronger parapopyhy- 

 sis, enclosing the large transverse foramen for the cer- 

 vical extension of the thoracic retia mirabilia. The 

 lower transverse process or parapophysis is broader 

 near the base than the upper process, its posterior sur- 

 face being rounded: it projects outward with a twist, 

 the distal end being bent nearly vertical, almost at right 

 angles to its basal portion and is likewise bent 

 backward. 



Fourth cervical. — The broadly elliptical anterior 

 face of the centrum is flattened and its posterior face is 

 shallowy depressed medially. The width of the neural 

 canal exceeds the vertical diameter. The pedicles of the 

 neural arch (pi. 17, fig. 7) are very short and support 

 ovoidal prezygapophysial facets which project forward 

 beyond the level of the anterior face of the centrum. 

 The oblique postzygapophysial facets are elongated and 

 also project backward beyond the level of the posterior 

 face of the centrum. A short triangular neural spine 

 (pi. 18, fig. 4) rises from the top of the neural arch. 

 The extremities of the diapophyses and parapophyses 

 are not united distally to completely enclose the fora- 

 men transversarium for accommodation of the cervical 

 extension of the thoracic retia mirabilia. Each thin di- 

 apophysis is dorsoventrally compressed on the basal 

 lialf of its length but is bent downward and attenuated 

 distally, the extremity of the right process being sepa- 

 rated from the end of the corresponding parapophysis 

 by a gap of at least 7 mm., and by 17 mm. on the left side. 



