MYOLOGY 49 



which is by fleshy slips from five of the ribs — the fourth 

 or fifth to the eighth or ninth. Rapidly converging, in- 

 sertion is by rather weak aponeurosis upon the medial 

 raphe just over the spine of the second thoracic vertebra 

 and partially superficial to the extreme caudal portion of 

 the splenius. 



In Neotoma origin seems always to begin at the fourth 

 rib and apparently does not extend beyond the seventh. 

 The muscle is so exceedingly thin in this subgenus that its 

 exact bounds are difficult of definition. In Teonoma origin 

 is from the fourth to tenth (inclusive) ribs, but very few 

 fibers come from the tenth. Insertion is weaker than in 

 Homodontomys, the medial fibers ceasing before the raphe 

 is reached. 



M. serratus posterior inferior (figs. 9, 10) has origin 

 from the last five ribs, with insertion upon the lumbodorsal 

 fascia. 



It may be noted that the apparent affiHation of this muscle 

 with the serratus posterior superior is sHght, and that in 

 practice, the division between it and the obliquus abdominis 

 internus is not to be distinguished with certainty. 



The innervation of these two muscles is by the inter- 

 costal nerves. 



2. Deep, intrinsic back muscles 



These are divisible into the 



Mm. splenius transverso-spino-occipital system 



long system deep, short system 



M. splenius (figs. 6, 8, 10, 24). This muscle fies deep 

 to the rhomboideus anticus and occipitoscapularis. As a 

 whole it has origin from the deepest part of the nuchal 

 Ugament, extending from the great spine of the second 

 thoracic vertebra to within 10 mm. of the occiput. In- 

 sertion is upon the caudal border of the lambdoidal crest 



