58 ELEMENTS OF MAMMALIAN ANATOMY 



last three thoracic vertebrae are characterized by mammillary 

 processes springing from the dorsolateral portion of the roots 

 of the anterior processes. 



The following features are common to all of the lumbar 

 vertchrce: a spinous process projecting dorsocraniad (Fig. 27); 

 a transverse process projecting ventrocraniad on either side 

 from the body; anterior articular processes and posterior articu- 

 lar 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 spin- 

 ous processes increase in length in the same order, and the 

 neural canal likewise enlarges caudally. 



The sacrum is a single bone (Fig. 28) formed by the union 

 of three sacral vertebras. The limit of each element is marked 

 by the dorsal and ventral intervertebral foramina which fur- 

 nish 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 portion of the bone presents 

 on its lateral aspect the auricular surfaces for articulation with 

 the ilium. This expansion appears to be a modified transverse 

 process. Prominent transverse processes also project from the 

 caudal angles. 



The caudal vertebrae vary greatly in number. According 

 to Mivart, there are only four in the Manx cat; and according 

 to Jayne, there may be as many as twenty-six in some varieties 

 of the common cat. The transverse processes and articular 

 processes become less prominent from the third vertebra to 

 the eighth or ninth, where they are present only as slight ridges. 

 The spinous process is present in the first three, but dwindles 

 to a ridge in the fourth. The first six or seven elements possess 

 a neural arch which more distally loses its roof, making the 

 neural canal a mere groove. The groove becomes fainter dis- 



