OF DIDELPHYS VIRGINIANA. 97 



size. The trapezius and rhomboideus are described under head of the anterior extremity ; 

 the cervicalis ascendens, transversalis cervicis, and spinalis and semispinalis cervicis in con- 

 nection with the muscles of the back, of which they are all merely the upward prolonga- 

 tions. The remaining muscles are : — 



Splenitis. — Exposed upon removal of the trapezius and rhomboideus. It forms, with its 

 fellow of the opposite side, an isosceles triangle whose base is the crista occipitis, and per- 

 pendicular the ligamentuni nuchas. There is no lower portion corresponding to the 

 "splenius colli," so called ; the muscle terminates below in a sharp, distinct point upon a 

 spinous process of a vertebra. It has unbroken origin from the ligamentum nuchge, and 

 by this from the spines of three or four upper dorsal and six lower cervical vertebrae ; forms 

 a moderately thick plane, with a thickened external border ; widens as it ascends, and is 

 inserted into the whole of the occipital crest. As the spinal origin of the muscle ends 

 with the axis, and the median border is not always directed straight forward, nor inserted 

 exactly on the middle line of the skull, it results that a small, triangular space between 

 the muscle and its fellow is often, or usually left. In this space the rectus posticus major 

 and part of the obliquus inferior appear. Otherwise, the splenius overlies and hides the 

 greater part of the nuchal muscles. 



Blventer cervicis. — On reflecting the splenius the following muscles more particularly 

 come to view : — biventer cervicis, coraplexus and trachelo-mastoideus, counting from the 

 spine outward, along the whole length of the neck, together with the two largest of the 

 head-muscles, and the several strips of muscle coming up from the back. The biventer lies 

 nearest the spinal column, and is ordinarily perfectly distinct fi'om the complexus ; but 

 liable to be partly or wholly blended with the latter, in which case it forms its medial bor- 

 der. Its name does not express its physical character ; it has no central tendinous part, 

 but only a slight constriction, produced by irregular, fibrous laminae, that form partial inter- 

 sections. It is the longest muscle of the back of the neck ; a sub-cylindrical strip, with 

 no definite attachments along its course. It arises by slips from the transverse processes 

 of the fifth, sixth and seventh dorsal vertebrce (but number of slips variable), lies in the 

 same plane as the complexus, and is inserted fleshy into all that (median) part of the 

 occipital crest not occupied by the following muscle. 



Complexus. — A very large and rather thick plane of fibres separating the foregoing from 

 the succeeding muscle ; there is nothing specially " complex" in its structure. It arises by 

 eight to ten long, slender, very distinct, fleshy fjisciculi from the anterior margins of the 

 bases of the articular processes of the six lower cervical, and two, three or four upper dor- 

 sal vertebrae. The lower fasciculi are much the longest, and rapidly diminish in length 

 from below upward ; uniting, without tendinous intersections, to form a single broad plane, 

 curving over toward the spine, its anterior border in relation to the biventer ; inserted by a 

 short, broad, dense, glistening aponeurosis into all, or nearly all, the occipital crest. The 

 muscle has also an attachment to the margin of the transverse process of the atlas, as it 

 passes over the latter. 



Trachelo-mastoideus. — Overlying the latter to the outer side ; a muscle of considerable 

 size. It arises by about ten long, slender, distinct, fleshy fasciculi from the articular pro- 

 cesses of the six lower cervical and three or four upper dorsal vertebrae, close by the ori- 

 gins of the complexus. These fasciculi soon blend, frequently with a slight tendinous 

 intersection, into a common plane, rather thin, and narrowing rapidly as it ascends, till it 



HlKMniRS BOST. 80C. NAT. HIST. TOL. II. M 



