22 



apophyses both before and behind. The thirteenth dorsal has the median zygapo- 

 physis in front but not behind : the costal surface has disappeared from the diapo- 

 physis. The fourteenth dorsal has only the ordinary pair of zygapophyses before and 

 behind, but may be distinguished from the second, third, fourth and fifth dorsals by 

 the absence of the costal articulation on the diapophysis, and of that on the upper 

 and hinder angle of the centrum. The fifteenth dorsal has an anapophysis on each 

 side with an articular surface, and has only the costal articulation on the neurapo- 

 physis. The sixteenth dorsal has on each side, at the fore part of the neural arch, a 

 parapophysis with a superior articular surface, and behind, an anapophysis with an 

 inferior articular surface. But it differs from the lumbar vertebrae by the costal sur- 

 face on the neurapophysis. 



Having now described the principal characters of those segments of the skeleton, 

 the centrums and neural arches of which are comprehended in Anthropotomy under 

 the term of ' true vertebrae,' on account of their freedom of motion on each other, I 

 next proceed to the description of the ' false vertebrae ;' and first, of those that, being 

 anchylosed together, form the ' sacrum.' 



This part of the skeleton includes five vertebrae (Plate VII. 1-5), which are not only 

 anchylosed to each other, but to both the iliac and ischial bones : the length of 

 the sacrum is 22 inches, its extreme breadth across the fifth vertebra, fig. 1, dt, is 

 20 inches. The centrum of the first vertebra (Plate VI. c) presents a transversely 

 oblong, subquadrate, flattened, articular surface for that of the last lumbar vertebra, 

 with its margin a little produced forwards, and developed below into a pair of rough 

 ridges, * *. The neural arch overhangs this surface, and developes a metapophysis 

 from the fore part of each side of its base, with a broad articular surface on its under 

 part, and a similar surface above (Plate VII. fig. 1, z), representing the anterior 

 zygapophysis ; the two surfaces meeting at a right angle at their inner borders. 

 The broad diapophysis of the first sacral, 1, is perforated by a small subvertical 

 canal, d', at its confluence with the ilium, and is separated from the corresponding 

 part of the next diapophysis by a larger orifice, o i, which is the first of the four 

 superior or posterior sacral outlets. The neural arch of the first sacral vertebra, n 1, 

 is separated from that of the second, «», by a narrow transversely elongated ellip- 

 tical vacuity. The neural arches of the three succeeding vertebrae are completely 

 confluent: a pair of triangular closely approximated apertures, n *, divides the base 

 of the neural spine of the fourth, ns *, from that, ns s, of the fifth sacral vertebra. The 

 neural spines of the first four sacral vertebrae have coalesced into a strong vertical 

 ridge, ns, ns «, increasing in thickness as it extends backwards, and being there from 

 two-thirds of an inch to one inch and a half thick across the broken summit. The 

 second posterior sacral canal, o 3, intervenes between the diapophysis of the second 

 and that of the third vertebra. The metapophysis, m «, of the fourth appears as a low 

 angular tubercle above and a little behind the diapophysis of the third sacral, 3. The 

 diapophysis of the fourth sacral, d 4, extends outwards beyond the ilium, as a sub- 



