OF THE BACK. 355 



tion of the spine, by means of two additional muscles, the Transversalis Colli, 

 and Traehelo-mastoid. 



The Transversalis Colli, placed on the inner side of the Longissimus Dorsi, 

 arises by long thin tendons from the summit of the transverse processes of the 

 third, fourth, fifth, and sixth dorsal vertebra, and is inserted by similar tendons 

 into the posterior tubercles of the transverse processes of the five lower cervical. 



The Traehelo-mastoid lies on the inner side of the preceding, between it and 

 the Complexus muscle. It arises by four tendons, from the transverse processes 

 of the third, fourth, fifth, and sixth dorsal vertebra, and by additional separate 

 tendons from the articular processes of the three or four lower cervical. The 

 fibres form a small muscle, which ascends to be inserted into the posterior mar- 

 gin of the mastoid process, beneath the Splenius and Sterno-mastoid muscles. 

 This small muscle is almost always crossed by a tendinous intersection near its 

 insertion into the mastoid process. 



The /Spinalis Dorsi connects the spinous processes of the upper lumbar and 

 the dorsal vertebrae together by a series of muscular and tendinous slips, which 

 are intimately blended with the Longissimus Dorsi. It is situated at the inner 

 side of the Longissimus Dorsi, arising, by three or four tendons, from the spi- 

 nous processes of the first two lumbar and the last two dorsal vertebras ; these 

 uniting, form a small muscle, which is inserted, by separate tendons, into the 

 spinous processes of the dorsal vertebrae, the number varying from four to eight. 

 It is intimately united with the Semispinalis Dorsi, which lies beneath it. 



The Spinalis Colli \s a. small muscle, connecting together the spinous processes 

 of the cervical vertebrae, and analogous to the Spinalis Dorsi in the dorsal re- 

 gion. It varies considerably in its size, and in its extent of attachment to the 

 vertebrae, not only in different bodies, but on the two sides of the same body. 

 It usually arises by fleshy or tendinous slips, varying from two to four in num- 

 ber, from the spinous processes of the fifth and sixth cervical vertebrae, and 

 occasionally from the first and second dorsal, and is inserted into the spinous 

 process of the axis, and occasionally into the spinous process of the two verte- 

 bras below it. This muscle was found absent in five cases out of twenty-four. 



The Complexus is a broad thick muscle, situated at the upper and back part 

 of the neck, beneath the Splenius, and internal to the Transversalis Colli and 

 Traehelo-mastoid. It arises, by a series of tendons, about seven in number, 

 from the tips of the transverse processes of the upper three dorsal and seventh 

 cervical, and from the articular processes of the three cervical above this. The 

 tendons uniting form a broad muscle, which passes obliquely upwards and in- 

 wards, and is inserted into the innermost depression between the two curved 

 lines of the occipital bone. This muscle, about its middle, is traversed by a 

 transverse tendinous intersection. 



The Biventer Cervicis is a small fasciculus, situated on the inner side of the 

 preceding, and in the majority of cases blended with it ; it has received its name 

 from having a tendon intervening between two fleshy bellies. It is sometimes 

 described as a separate muscle, arising, by from two to four tendinous slips, from 

 the transverse processes of as many of the upper dorsal vertebrae, and inserted, 

 on the inner side of the Complexus, into the superior curved line of the occi- 

 pital bone. 



Relations. The muscles of the fourth layer are bound down to the vertebrae 

 and ribs in the dorsal and lumbar regions by the lumbar fascia and vertebral 

 aponeurosis. Their inner part covers the muscles of the fifth layer. In the 

 neck they are in relation, by their superficial surface, with the Trapezius and 

 Splenius ; by their deep surface, with the Semispinalis Dorsi and Semispinalis 

 Colli and the Recti and Obliqui. The Biventer Cervicis is separated from its 

 fellow of the opposite side by the ligamentum nuchae, and the Complexus from 

 the Semispinalis Colli by the profunda cervicis artery, the princeps cervicis 

 artery, and by the posterior cervical plexus of nerves. 



Nerves. The Erector Spinae and its subdivisions in the dorsal region are sup- 



