10 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 
vertebra. At the caudal margin of the ventral surface there 
is a notch between the lateral mass and the centrum (g). 
When the caudal vertebre 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 (4) 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 vertebra. 
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 laminz of the sacral vertebra. 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 vertebre. 
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, ¢). 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 
