224 AIVATOJnCAL TECHJSOLOGT. 



Posture. — Latericiambent, with a block transversely under tlie 

 neck. The posture must be changed often and greatly in the course 

 of the expesui'e and dissection. 



Expostire. — By the reflection of the clavo-irapezius, sierno- 

 Tnastoideus and claiio-deltoideus. Note that, after the reflection of 

 the above named muscles and the occipiio-scapularis, the broad 

 transverse process of the atlas is covered, dorsally, by a thick mass 

 of muscle, the most ectal of which, the splenius (Fig. 67), presents 

 a smooth and convex surface. Eemove this mass by deep incisions 

 with the arthrotome as follows : Laterad from the cephalic end of 

 the origin of the rhomboideus ; then cephalad to the occiput ; then 

 laterad close to the occiput, but without severing any of the muscu- 

 lar attachments along the crest ; finally, beginning with the meson, 

 dissect up the mass from the vertebrae. 



General Description. — Narrow, tseniate, from the hasioccipital 

 hone (Fig. 57) and atlantal transverse process or diapopTiysis 

 (Fig. 52) to the metacromion (Fig. 44). 



Dissection. — The dorsal border of the scapular end has been indi- 

 cated (§ 614) in connection with the insertion of the cephalic border 

 of the acromio-trapezius. Trace it cephalad, and draw the middle 

 of the muscle dorsad so as to indicate its ventral border. 



In reflecting the caudal part, note a lympJiatic gland close to the 

 coracoid border of the supraspinatus. In reflecting the cephalic 

 part, note that, a little caudad of the atlantal transverse process, its 

 plane gradually changes from dorso-ventral to dextro-sinistral, and 

 that there are signs of subdivision. 



Eemove the muscles ventrad and cephalad of the atlantal trans- 

 verse process, but without cutting the attachment of this muscle to 

 its ventral surface. Feel for the prominent auditory bulla just 

 mesad of the M. masseter and the meatus, and carefully dissect 

 off the M. digastric^is, which covers it. Avoid the external carotid 

 artery which skirts the meso-cephalic border of the bulla, and the 

 Tiyoid arcJi (Fig. 30) which lies imbedded in the muscles between 

 it and the artery. 



Then use the tracer to clear away the connective tissue, and the 

 arthrotome to scrape the ventral surface of the transverse process 

 of the atlas, excepting where it is occupied by the origin of the lev- 

 ator claviculcB. Between the border of the process and the larynx 

 and trachea note and remove the lateral lobe of the thyroid body. 



