12 THE SKELETON 



splenius colli, intertransversales, interspinales, levator anguli scapula?, transversalis 

 cervicis, scalenus medius, seniispinalis colli, and niultifidus spinae. 



To the seventh : — Ti-a])ezius, complexus, serratus posticus superior, splenius, 

 rhomboideus minor, niultilidus spina.% seniispinalis, eight intertransversales, inter- 

 spinales, levator costa% scalenus posticus, accessorius, scalenus rnedius, trachelo- 

 mastoid, and the longus colli. 



THE THORACIC OR DORSAL VERTEBRA 



The general characters of the thoracic vertebrae have already been considered 

 in tlie description of the type verte])ra. Their most distinguishing features are the 

 facets on the transverse processes and sides of the bodies for the tubercles and 

 heads of ribs. 



Peculiar thoracic vertebrae. — Several vertebra? in this series differ from the 

 type form. The exceptional are — the first, ninth, tenth, eleventh, and twelfth. 



The first has a Iwdy resembling a cervical vertebra, the upper s\n-face being 

 concave and lipped laterally; it has two entire facets above for the first pair, and 

 two demi-facets below for the second pair of ribs. The spinous process is thick, 

 strong, almost horizontal, and more prominent than that of the vertebra promi- 

 nens. Occasionally the transverse process is perforated near its root. 



The ninth has demi-facets above, and usually none below; when the inferior 

 demi-facets are i)resent, this vertebra is not exceptional. 



The tenth usually has an entire costal facet at its upper border, on each side, 

 but occasionally only demi-facets. It has no loAver demi-facets, and the facets on 

 the transverse processes are usually small. 



The eleventh has a large body resemliling a lumbar vertebra. The rib facets are 

 on the pedicles; they are complete and of large size. The transverse processes 

 are short and have no facets for the tubercles of the eleventh pair of ril^s. 



In many mammals, the spines of the anterior vertebrae are directed backwards, 

 and those of the posterior directed forwards; in the centre of the column there is 

 usually one spine vertical. This is called the anti-clinal vertebra. It is at this 

 ])oint that the thoracic begin to assume the characters of lumbar vertebrae. In 

 man, the eleventh thoracic is the anti-clinal vertebra. 



The twelfth resembles in general characters the eleventh, but may be distin- 

 guished from it in having the inferior articular processes convex and turned 

 outwards as m the lumbar vertebrae. It also resembles a lumbar vertebra b)'' pos- 

 sessing well-marked mammillary and accessory tubercles. These tubercles are 

 occasionally present on the tenth and eleventh vertebrae. 



A peculiarity, more frequent in the thoracic and lumbar than in the cervical 

 and sacral regions of the column, is the existence of a half-vertebra. Such speci- 

 mens have a wedge-shaped half-centrum, to which are attached a lamina, a trans- 

 verse, superior and inferior articular, and half a spinous process. As a rule, a 

 half-vertebra is ankylosed to the vertebra; aljove and below. 



LUMBAR VERTEBRAE 



The distinguishing features of lumbar vertebrae are their large size; the margins 

 of the centrum are prominent; the pedicles are stout and strong; the inferior 

 intervertebral notches are deep, and the laminae are thick and strong. The sujx-rior 

 articular ])rocesses have concave facets directed l)a(kwar(ls and inwards, and their 

 ]»()steri()r l)orders are surmounted by rounded mammillary ]irocesses or tul)ercles. 

 The infciior articular processes have facets which look forwards and outwards. 

 The transverse ]tn)cesses are long, slender, and each presents near the base, on the 

 posterior aspect, a small accessory tubercle. The spinous })rocesses are thick, 

 broad, and project horizontally l)ark\vards. 



Tlie transverse processes of tlie kuiibar vertebrae are more complex than they at first 

 ajipear. Each is c(imi>uuiiiled of a transverse and a costal jirocess. The accessory jirocess represents 



