64 HEAD AND NECK 



superficial surface of this muscular mass is covered by and is adherent to 

 the posterior layer of the lumbo-dorsal fascia. 



Superiorly, the sacro-spinalis divides into three columns. The lateral 

 column first separates from the general mass, and to it the name of ilio- 

 costalis is given ; the intermediate column is termed the longissimus, and the 

 medial column, which becomes quite distinct only as the upper part of the 

 thoracic region is approached, is called the spinalis. The semispinalis 

 muscle also is included in the third layer. 



The Ilio-costalis is a column of muscular bundles which extends from 

 the lumbar to the cervical region. It is separable into three segments, 

 known, from below upwards, as the ilio-costalis Inmborum, the ilio-costalis 

 dorsi, and the ilio-costalis cervicis. 



Ilio-costalis Lumborum. The lumbar part of the ilio-costalis muscle 

 and the longissimus dorsi become distinct at the level of the last rib, and 

 the interval between them is marked by the exits of the lateral divisions of 

 the posterior rami of lower thoracic nerves. 



The ilio-costalis lumborum ends above in a series of six or seven slender 

 tendons, which are inserted into the angles or the corresponding parts of 

 the lower six or seven ribs. 



The nio-costalis Dorsi (O.T. Musculus Accessorius] arises by six or seven 

 slender tendons from the angles of the lower ribs, on the medial sides of the 

 tendons of insertion of the ilio-costalis lumborum, and it is inserted by a 

 series of similar tendons into the angles of the upper six ribs and to the 

 transverse process of the seventh cervical vertebra. 



The Ilio-costalis Cervicis (O.T. Cervicalis Ascendens] is the highest 

 segment of the ilio-costalis. It arises, on the medial side of the ilio-costalis 

 dorsi, by four slips which spring from the third, fourth, fifth, and sixth ribs ; 

 it is inserted into the transverse processes of the fourth, fifth, and sixth 

 cervical vertebrae. 



Dissection. To display the ilio-costalis properly, the dissector 

 should first evert the lowest segment, and then in turn the 

 middle and upper segments aside, but whilst doing that he must 

 take care to preserve the lateral divisions of the posterior rami of 

 the spinal nerves. 



The Longissimus is the middle and largest of the three muscle columns. 

 It extends upwards, through the thoracic and cervical regions, to the head, 

 and it also is separable into three segments : longissimus dorsi, longissimus 

 cervicis, and longissimus capitis. 



Dissection. The interval between the longissimus and the 

 spinalis is frequently difficult to define, but if the fascia is care- 

 fully cleaned from the lateral to the medial border of the longis- 

 simus, in the upper thoracic region, the separation will become 

 apparent, and after it has been found the attachments of the 

 longissimus must be defined. The muscle being displaced to 

 the medial and lateral sides as may be necessary. 



Longissimus Dorsi. The thoracic part of the longissimus possesses two 

 rows of slips of insertion : a medial row of tendinous slips which are 

 attached to the tips of the transverse processes of the thoracic and the 

 accessory processes of the lumbar vertebrae, and a lateral row of muscular 

 slips which are inserted into the lower ten ribs, on the lateral sides of their 

 tubercles, and to the transverse processes of the lumbar vertebrae, and to 

 the posterior surface of the middle lamella of the lumbar fascia. 



Longissimus Cervicis (O.T. Transversalis Cervicis}. The cervical 



