46 ELEMENTS OF MAMMALIAN ANATOMY. 



trad or ventromediad ; a body whose transverse diameter is 

 greater than the vertical diameter ; and transverse processes. 

 There are two half facets on each side of the body of every 

 thoracic vertebra except the first, eleventh, twelfth, and 

 thirteenth. The head of a rib thus articulates with two 

 vertebrae (Fig. 28). The body of the first vertebra bears 

 on each side a whole facet and a half facet. The eleventh, 

 twelfth, and thirteenth bear a whole facet on each side of 

 the body. 



The transverse processes of the first eleven bear facets 

 for the articulation with the tubercles (Fig. 25) of the 

 ribs. The last three thoracic vertebrae are characterized by 

 mammillary processes springing from the dorsolateral por- 

 tion of the roots of the anterior processes. 



The following features are common to all of the lumbar 

 vertebra: a spinous process projecting dorsocraniad (Fig. 

 26) ; a transverse process projecting ventrocraniad on either 

 side from the body; anterior articular processes and poste- 

 rior articular processes. A mammillary process is present 

 on the root of the anterior articular process of the first five 

 bones, and an accessory process occurs on the caudal margin 

 of the wall of the neural arch of all except the last vertebra. 

 The transverse processes increase in length and curvature 

 caudally. The spinous processes increase in length in the 

 same order, and the neural canal likewise enlarges caudally. 



The sacrum is a single bone (Fig. 27) formed by the 

 union of three sacral vertebras. The limit of each element 

 is marked by the dorsal and ventral intervertebral foramina 

 which furnish passage for the dorsal and ventral branches 

 of the spinal nerves. The two tubercles on either side of 

 each of the three median spinous processes are the result 

 of the fusion of the articular processes. The cranial por- 

 tion of the bone presents on its lateral aspect the auricular 



