62 PROFESSOR HUXLEY ON THE OSTEOLOGY OF THE GENUS GLYPTODON. 
directly forwards, its long axis being horizontal and at right angles to the axis of the 
spinal canal. The facet is 1*8 inch long by 09 inch maximum height. 
This articular facet is separated by a deep groove, into the bottom of which a large 
canal ( d ) opens, from two other articular surfaces (b, c ), placed one immediately above 
the other, and also parted by a deep channel, which may be regarded as an internal 
branch of the groove. 
The lower articular face (c), almost flat, looks inwards and forwards ; and its long axis, 
which continues the direction of the floor of the neural canal, is inclined from above 
downwards and outwards. 
The upper facet (b), also flat, and, elongated transversely, looks directly upwards. Its 
inner end is nearer the lower facet than its outer end ; and a well-marked fossa or 
depression lies behind it. The upper articular surface certainly answers to the anterior 
oblique process or “ prezygapophysis ” of the seventh cervical vertebra. The nature of 
the lower and of the outer facet will only become obvious when the characters of the 
cervical vertebrae of recent Armadillos have been explained. The anterior face of the 
spinous process of the trivertebral bone exhibits two ridges, each convex towards the 
middle line, which divide the face into a middle and two lateral areae. 
The upper face of the bone (Plate VII. fig. 3) presents three pairs of foramina, termi- 
nating internally in canals which lead into the spinal canal, and externally opening into 
recurved grooves on the surface of the bone. The middle apertures are the largest, and 
the corresponding grooves more strongly defined and wider. The posterior apertures 
are smallest, and are situated quite close to the hinder margin. The surface of the bone 
between these apertures is rough and irregular. The margins of this face of the bone 
are produced into three processes which alternate with the foramina. The hindermost 
of these processes is the largest, and ends in a point which is somewhat recurved and 
bent down. 
A side view of the trivertebral bone (Plate VII. fig. 6) shows that these processes are 
continued into irregular vertical ridges, between which two fossae are enclosed. Of 
these, the anterior is much deeper and more capacious than the other. It is an irre- 
gular cavity subdivided by a vertical ridge into two, each of which presents a somewhat 
deeper fossa at its inner and lower end. 
The second, shallower, fossa, which lies between the hinder face of the middle process 
and the front face of the posterior process, presents an elongated irregular articular 
facet on its anterior wall, and a more rounded articular surface on its posterior wall. 
The second rib is received into this fossa, and articulates with both these facets. 
The posterior face of the third process presents a small, slightly concave, oval arti- 
cular face on its lower half, with which the third rib was doubtless connected. 
The posterior aspect of the trivertebral bone (Plate VII. fig. 4) presents for notice, 
besides the features already mentioned, several others. The neural arch of the hindermost 
vertebra of the three overhangs ; and its under face exhibits two oval slightly concave 
articular faces (a, a), the posterior oblique, or “ postzygapophysial,” surfaces of the 
