32 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 70 



Definition of the superficial divisions and of the cervical portion 

 of the long system of the back musculature was entirely satisfactory, 

 but preservation was so poor that any disturbance of the deeper 

 portion resulted in the fibers falling apart in inextricable confusion, 

 so that the deeper fibers were not investigated. Equally unfortunate 

 id the fact that the peduncle was somewhat hardened and suffered 

 further desiccation during dissection, so that the tendons in this 

 region could not be precisely followed. 



From the ectal aspect the central dorsal region of the longissimus 

 mass of the long system is indivisible save for a thin medial sheet 

 (fig. 11) which may be separated from the underlying fibers from 

 about the sixth thoracic to the third or fourth lumbar vertebra. The 

 homology of this sheet is not certain, although its relationship prob- 

 ably lies with the spinalis dorsi, occurring as a distinct muscle in 

 most mammals. The muscle mass underlying this could not be 

 separated and the fibers originate apparently from both the spinous 

 and most of the transverse processes of the vertebrae concerned. 



Progressing caudad, there is gradual separation of this single 

 longissimus belly into a dorso-medial longissimus dorsi, arising from 

 the spinous proceses, and an iliocostalis lumborum^ with origin from 

 the medial three quarters of the transverse processes. Toward the 

 peduncle these two divisions constitute A^ery distinct muscles, each 

 invested hy a tough, glistening aponeurosis. The}' both develop 

 strong tendon bundles in this region, which increase in strength and 

 size caudad until the muscle fibers cease entirely. 



Laterad of the splenius is a heaA^y muscle continuous with the long- 

 system and undoubtedly constituting what in this case may be 

 termed a longissimus capitis et cervicis. The more ventral fibers 

 originate from the vicinity of the tubercula of the first four (?) ribs. 

 Passing latero-craniad, insertion is upon the membrane over the bor- 

 der of the exoccipital and upon the transverse process of the atlas as 

 well. An effort was made to separate this mass into two distinct 

 muscles on a line between the cervicis and capitis portions, but with- 

 out success. 



Largely deep to the splenius there is a broad muscle continuous 

 craniad with the long system which apparently constitutes a semi- 

 spinalis capitis. It is separable with ease, and the more, superficial 

 division must therefore be termed the hiventer cervicis, and the 

 deeper, complexus. The fibers of the biventer which do not continue 

 directly from the indivisible longissimus have origin from the lateral 

 portion of the transverse processes of several of the thoracic verte- 

 brae and the tubercula of their ribs. Insertion is along the entire 

 supraoccipital from practically the middorsal line to a point on the 

 exoccipital caudad of the zygomatic process of the squamosal. 



