40 



THE SKELETON OF THE HORSE 



foramina (Foramina saoralia dorsalia); the dorsal branches of the sacral nerves 

 emerge through them. 



The ventral or pelvic surface (Facies pelvina) is concave in its length, wide in 

 front, narrow behind. It is marked by four more or less distinct transverse lines 

 (Lineffi transversa), which indicate the demarcation of the bodies of the vertebra^. 

 At the ends of these lines are the ventral sacral foramina (Foramina sacralia 

 ventralia), which are larger than the dorsal series and diminish in size from first 

 to last; they transmit the ventral divisions of the sacral nerves. 



The dorsal and ventral foramina comnmnicate with the sacral canal and are 

 together equivalent to the usual intervertebral foramina. 



Fig. 19. — S.\crum of Horse, Dorso-later.\l View. 

 C, Body of first sacral vertebra; ^1, arch of first vertebra; Cs, sacral canal; P.s. 1-5, sacral spines; P.t., 

 wings of sacrum; 1, 1', surfaces for articulation with transverse processes of last lumbar vertebra; F.a., auricular 

 surface; 2, 2', articular processes; 3-6, dorsal sacral foramina; 7, interarcuate space; 8, lateral border; h, apex. 

 (Struska, Anat. d. Haustiere.) 



The lateral borders are rough, thick in front, thin behind. 



The base (Basis ossis sacri) is directed forward, and is relatively very wide. 

 It presents centrally the body of the first sacral segment, which is wide transversely, 

 flattened dorso-ventrally, and has a rounded surface which articulates with the 

 last lumbar vertebra through the medium of an intervertebral fibro-cartilage. 

 The ventral margin projects slightly, forming the promontory (Promontorium). 

 Above the body is the entrance to the sacral canal, flanked by a pair of articular 

 processes, which project upward and forward from the arch, and have concave 

 surfaces internally for articulation with those of the last lumbar vertebra. On 

 each side of these is a smooth notch which is converted into a foramen by apposition 

 with the last lumbar. The lateral parts of the base, the wings or alae (Ala? sacrales), 



