428 SCHULTE, SEI WHALE. 



to the spines by far the greatest area is occupied by the longissimus, which increases in bulk as 

 far rostrad as the thorax, there diminishing so that only a ribbon-like band, narrow and deep, 

 is continued to the head. Between this and the transversarius, beginning in the upper thorax, 

 is interposed the triangular trachelo-mastoid, which is well demarcated from the longissimus by 

 a strong septum, while less firm and but scanty connective tissue intervenes between it and 

 the transversarius. It seems to receive no fasciculi from that muscle. The longissimus abuts 

 upon the spines in the pedicle, yet even here fasciculi of the transverso-spinalis tract separate 

 it deeply from their bases. These elements increasing in size rostrad come to occupy more and 

 more of the sides of the spines and in the upper lumbar region form a narrow tract intervening 

 between the longissimus and the spines. In this region the separation of the two muscles is 

 very imperfect. From the last dorsal vertebra the superficial stratum of the transverso-spinalis, 

 the semispinalis, increases enormously in size and forces the diminishing longissimus laterad, 

 its very massive belly (semispinalis capitis) is the largest muscle of the neck and gains a broad 

 and deep insertion upon the occipital. Superficial and partly concealing this muscle in the 

 neck is the splenius capitis, which inserts in intimate association with the trachelo-mastoid into 

 the mastoid region. With this by way of introduction we may turn to a brief consideration of 

 the individual muscles. 



The splenius arises from the aponeurosis covering the longissimus by means of which it 

 is attached to the spines in the dorsal region. Its fasciculi are directed rostrad and laterad, 

 and condensing towards its insertion and blending to some extent with the trachelomastoid, it 

 inserts into the caudal extremity of the squamosal close to its junction with the mastoid and 

 into a strong tendon, which passes rostrad from this region to the postorbital process of the frontal 

 and the base of the zygoma. In its course this tendon is adherent to the underlying periosteum. 

 It gives insertion caudad in addition to the splenius and trachelomastoid, to some of the fasci- 

 culi of the sternomastoid and mastohumeral. In front it gives origin in part to the deep portion 

 of the masseter. 



The trachelomastoid is of moderate size and triangular in shape. It arises from the ectal 

 surfaces of the first four ribs, mesal to the transversarius slips, and from the transverse processes 

 of the lower cervical vertebrae. It is inserted, fused with the splenius, into the caudal portion of 

 the squamosal and into the tendon just described. 



The longissimus dorsi occupies the region between the transverse and the spinous processes 

 as far as the thorax, where it is displaced laterad, yielding an increasing area immediately adja- 

 cent to the spines to the transversospinalis (semispinalis capitis). Here the muscle rapidly 

 diminishes in size and only a rather slender belly gains attachment to the exoccipital. In the 

 pedicle a ventro-lateral portion, the iliocostalis (sacrolumbalis of Stannius) is distinguishable, 

 separated from the dorso-median portion by a fibrous septum, which is nevertheless pierced for 

 the passage of tendons which give origin to fasciculi of the iliocostalis. Rapp considered that 

 the two portions were so intimately united as to constitute a single muscle. Stannius found them 

 separated throughout by a septum and assigns all the fasciculi that insert into transverse pro- 

 cesses and ribs to his sacrolumbalis. The longissimus begins by a stout tendon arising from the 

 dorsum of the last vertebra. It passes rostrad receiving slips from the spinous processes, 

 muscular fasciculi first appearing near the extremity of the pedicle. Throughout the caudal 

 and lumbar region it is recruited by slips from the spinous and accessory processes, and con- 

 tinues to receive slips from the latter source in the thorax, where it has abandoned its posi- 

 tion beside the spines. In addition it receives augmentation of fasciculi from the strong 



