12G ANATOMY OF UPPER EXTREMITY, ETC. 



occiput to the sacrum, and another from just below the middle of the 

 dorsal vertebras to the acromion of the scapula; the flaps, thus formed, 

 are to be raised and reflected. 



The muscles of the back, always difficult to dissect neatly, are often 

 made more so, by the intiltration of fluids which have gravitated to this 

 part of the body, while it remained dependent. The subcutaneous 

 cellular tissue is sometimes so much thickened by this infiltration, 

 that it is difficult to tell when the plane of the muscles is reached. 

 If this condition of things exist, care must be taken not to go through 

 the thin aponeurotic tendons by a too hasty incision. 



The dissection of the back is usually made for the benefit of the 

 class in common (with the exception of the cervical region, which 

 belongs more properly to the head), and is generally accomplished by 

 two of the class, the others assisting by reading the description of the 

 parts successively dissected. The student must be prepared to find 

 a great want of conformity between the muscles, as he finds them, 

 and the precise description of their origins and insertions as given in 

 books, for they have little of the distinct arrangement elsewhere to be 

 found. Of many, the fibres are so short, or so incompletely separated, 

 that their isolation is extremely difficult. "The deeper ones," says 

 John Bell, " might fairly be reckoned as one muscle, since they are 

 one in place and in office, but which the anatomist may separate into 

 an infinite number, with various and perplexing names, an opportu- 

 nity which anatomists have been careful not to lose." 



The trapezius and the latissimus dorsi muscles form th 

 superficial layer, and together cover the whole region oJ 

 the back. 



The TRAPEZIUS MUSCLE arises by a thin aponeurotic ten- 

 don (easily divided and injured if much care is not taken), 

 from the occipital protuberance and adjacent part of the 

 superior curved line of the occipital bone, from the ligt 

 mentum nuchse, and from the spinous processes, and supra- 

 spinous ligament of the last cervical vertebra, and of 

 variable number (six to twelve) of those of the dorsal re- 

 gion ; from this extended origin the fibres converge, so as 

 to give the muscle a triangular shape, and are inserted int< 

 the outer third of the clavicle, the acromion process, am 

 the spine of the scapula. The spinal accessory nerve 

 pierces the anterior border of this muscle and is distributed 

 to its fibres. 



The LIGAMENTUM NUCH^E is a strong layer of elastic 

 fibrous tissue, extending from the spine of the occiput to 

 that of the seventh cervical vertebra ; it is a rudimentary 

 development of the elastic band which serves to sustain 

 the weight of the head in the Ruminantia. 



The LATISSIMUS DORSI MUSCLE arises from the spiuous 



