42 U.S. NATIONAL MUSEUM BULLETIN 273 



have their highest insertion on the enlarged and bifid spinous process 

 of the axis (fig. 15). The longer and more superficial bundles reach 

 cranially only to the spine of C 4. The segments of the midthoracic 

 region are thinner than the rest. 



M. semispinalis capitis (fig. 15): This powerful and well -developed 

 muscle has a fleshy origin from the articular processes of the last five 

 cervical vertebrae, and by short tendinous fascicles from the meta- 

 pophyseal tubercles of T 1 to T 4. All these bundles are fused wuth 

 m. spinalis capitis into a single thick belly attached to the occipital 

 squama. Spinalis fibers are medial to those of the semispinalis of 

 which those coming from the metapophyseal structures present a 

 short tendinous interruption in their middle (biventer cervicis). 



Mm. rotatores: They constitute the deepest stratum of the oblique 

 system and are present only in the thoracic region. The rotatores are 

 segmentally arranged into pairs. A rotator brevis goes from a meta- 

 pophysis to the spine of the vertebra just craniad and a rotator longus 

 passes up to the spine of the second vertebra in the same direction. 



M. extensor caudae medialis: This muscle is the caudal extension 

 of the deep oblique system and occupies the vertebral groove of the 

 lower lumbar vertebrae, and its extension into the sacral and caudal 

 regions. The extensor medialis is segmented throughout its extent. 

 A typical unit, such as is found in the proximocaudal region, is com- 

 posed of fieshy fibers with origin in the spinous tubercles of two adjacent 

 vertebrae and the ligaments joining them. They run caudolaterally, 

 forming a tapering belly which is continued by a round tendon. This 

 attaches to the proximal articular process of the vertebra four seg- 

 ments caudally removed from the first included in the unit. 



According to Sirena (1871), M. complexus maior (m. semispinalis 

 capitis) arises from (1) the transverse processes of the last six cervical 

 and first five thoracic vertebrae, and (2) the spines of T 1 to 4. Bundles 

 with a spinous origin correspond, in my opinion, to m. spinalis capitis, 

 which is fused to the capitis part of the deep oblique system. His 

 observation of an origin from the transverse processes of the cervical 

 vertebrae is not correct. M. longissimus cervicis et capitis occupies 

 the space between the transverse and the articular processes in that 

 region (see fig. 14). It lies lateral to the elements of the deep oblique 

 system which, therefore, cannot arise from the said transverse proc- 

 esses, but from the crest formed by the articular ones of the cervical 

 vertebrae (see fig. 15). Sirena (1871) describes the complex of the 

 semispinalis and multifidus as extending from the spine of the axis to 

 the sacral region where it is said to continue into the tail as the m. 

 lumbosacrococcygeus of Vicq d'Azyr (m. extensor caudae medialis). 

 He does not differentiate between rotatores breve and longi. 



