VERTEBRAL COLUMN 



137 



small facets on its posterior margin for the heads of the first ribs. It has foramina 

 transversaria, and usually two foramina in either side of the arch. 



The dorsal arch of the atlas bears a large tuberosity. The ventral tubercle is 

 long, compressed laterally, and projects back under the axis. The wing is flattened 

 and bears a posterior tuberosity. The foramen trans versarium passes through the 

 posterior border of the wing to the fossa under the latter, and is not visible dorsally ; 

 it is sometimes very small or absent. The sides of the vertebral foramen bear 

 two lateral projections which partially divide it into a ventral narrow part, which 

 receives the odontoid process, and a dorsal larger part for the spinal cord. In the 

 fresh state the division is completed by the transverse ligament, which is attached 

 to the projections. 



The axis has a large spinous process, which is directed upward and backward. 

 The odontoid process is a thick cylindrical rod. The transverse process is very 

 small and the foramen transversarium is often incomplete. 



The thoracic vertebrae are often fifteen in number. Their bodies are relatively 

 long, constricted in the middle, and without ventral crests. Their extremities are 



Fig. 106. — Atl.\s of Pig, Dorsal View. 



a, Wing; h, ventral tubercle; c, foramen transver- 

 sarium; d, alar foramen; e, intervertebral foramen; /, dor- 

 sal tubero.sity; g, articular surface corresponding to that of 

 posterior articular process of typical vertebra; h, facet on 

 ventral arch for odontoid process. (Ellenberger-Baum, 

 Anat. d. Haustiere.) 



Fig. 107. — Axis of Pig, Left L.\ter.\l View. 

 a. Odontoid process (dens); b, spinous process; 

 c, anterior articular process; d, posterior articular pro- 

 cesses; e, transverse process; /, foramen transversar- 

 ium; (J, bar of bone which bounds h. intervertebral 

 foramen; i, vertebral foramen. (Ellenberger-Baum, 

 Anat. d. Haustiere.) 



elliptical, depressed in the middle and prominent at the periphery. The arch is 

 perforated by a foramen on either side, and in most of the series there is also a 

 foramen in the posterior part of the root of the transverse process which communi- 

 cates with the former or with the posterior intervertebral foramen. Sometimes 

 there is a foramen in the anterior part of the process also. There are mammillary 

 processes except on the first two; in the posterior five or six vertebrae they project 

 from the anterior articular processes. The facet for the tubercle of the rib is 

 absent or fused with that for the head in the last five or six. The last transverse 

 process is lumbar in character, plate-like, and aliout an inch (2 cm.) long. Small 

 accessory processes occur in the posterior part of the region. The first spinous 

 process is broad, very high, and inclined a little forward. The others diminish 

 very gradually in length to the tenth, beyond which they are about equal. The 

 second to the ninth are inclined backward, the tenth is vertical (anticlinal), and the 

 rest incline forward. The width decreases decidedly from the fourth to the tenth, 

 beyond which there is a gradual increase. The summits are slightly enlarged and 

 lie almost in a straight line. 



