io THE SKELETON OF THE CAT. 



the passage of sacral nerves. At the end of the second ridge 

 is a pair of ventral sacral foramina (/'), smaller than the first 

 pair and continued laterocaudad into shallow grooves for the 

 ventral rami of the sacral nerves. That portion of the bone 

 lying laterad of a line joining the medial borders of these two 

 pairs of foramina is known as the lateral mass of the sacrum 

 and is composed of the fused transverse processes of the sacral 

 vertebrae. At the caudal margin of the ventral surface there 

 is a notch between the lateral mass and the centrum (). 

 When the caudal vertebrae are articulated, this notch helps to 

 form a foramen for the third sacral nerve. 



The dorsal surface (Fig. 6) is narrower at its cranial end 

 than is the ventral surface. Its cranial border bears laterally 

 a pair of cranial articular processes (b} with their medially- 

 directed facets and between them it is concave, so that a large 

 dorsal opening is left into the vertebral canal between the last 

 lumbar vertebra and the sacrum. Caudad of the articular 

 processes are two pairs of tubercles (/). These are the fused 

 cranial and caudal articular processes of the sacral vertebras. 

 Caudad of them are the caudal articular processes of the last 

 sacral vertebra (d}. Craniolaterad of the middle and cranial 

 tubercles are dorsal (posterior) sacral foramina (g) for the 

 transmission of the dorsal rami of the sacral nerves. Three 

 spinous processes (a) appear between these rows of tubercles. 

 They decrease in height caudad. That part of the surface in- 

 cluded between the spinous process and the tubercles is made 

 up of the fused laminae of the sacral vertebrae. That part 

 between the tubercles and a line joining the lateral margins of 

 the dorsal (posterior) sacral foramina is formed by the fused 

 radices of the sacral vertebrae. 



The lateral surface may be divided into two parts. Craniad 

 is a large rough triangular area with equal sides and with one 

 of its angles directed ventrocraniad. It is the lateral face of 

 the pseudo-transverse process of the first sacral vertebra (Fig. 

 6, c). A smooth curved surface (the auricular facet) along its 

 ventral edge articulates with the ilium, while the dorsal por- 

 tion is rough for attachment of ligaments. Caudad is the 

 narrow longitudinal triangular area of the lateral faces of 



